BIOCHEM Q&A

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Dr. N. MALLIKARJUNA RAO

Questions and Answers


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BIOCHEMISTRY - Questions and Answers



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Dr. N. MALLIKARJUNA RAOProfessor & HOD

Department Of Biochemistry

Vishnu Dental College, Bhimavaram - 534202.



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Published by

HEAD OFFICE:

No. 225/B, 9th ‘A’ Main, Vijayanagara, Bangalore - 560 040.

Phone : 080 23407999 Mobile : 9980396967, Fax : 080 23302032

Email: [email protected] / [email protected] Website: www.seekaybooks.com

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BIOCHEMISTRY : Questions and Asnwers

Dr. N. MALLIKARJUNA RAO

© 2013 SEEKAY Publications

First Edition : 2013

ISBN : 978-81-924169-3-9

All rights reserved. No part of this book may be reproduced or transmitted in

any form or by any means, electronic or mechanical. Including photocopying,

recording, or any information storage and retrieval system without

permission, in writing from the author and the publisher.

Printed & Designed by :

M.M. PRINTERS, Anjananagara, Bangalore-560091.


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PrefaceThis book is written to help student in their preparation for

examinations. It meets needs of first year M.B.B.S., B.D.S.,

B.Sc.(N), B.P.T., M.Sc (Medical) and second year B.Pharm

students. Topics prescribed by Various Health Science,

Universities in India Vijayawada are included in the book. In

this book questions and answers are given for 21 topics.

Complex pathways are presented in a easy to remember way.

This book is written in such way that learning of questions and

answers given in each chapter makes student to acquire concept

or theme of that topic simultaneously. The book contains 495

questions. Of this answers are provided to 249 questions

remaining are model questions. Answers to 54 essay questions,

110 short questions and 85 very short or brief questions are

given in this book. Answers are given in simple language with

necessary diagrams or illustrations. Model questions given

enhances students ability to answer questions with alteration.

I am grateful to Sri K. Prasanna Kumar of Seekay Publications

for publishing the book.

BHIMAVARAM DR. N. MALLIKARJUNA RAO


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Contents 1. Cell, Membrane and Transport 001

2. Carbohydrates 007

3. Proteins, Plasma Proteins, Aminoacids and Peptides 013

4. Lipids 029

5. Enzymes 039

6. Nucleotides and Nucleic acids 058

7. Biological oxidation 068

8. Carbohydrate Metabolism 076

9. Lipid Metabolism 102

10. Protein and Amino acid Metabolism 120

11. Porphyrin and hemoglobin Metabolism 141

12. Nucleotide Metabolism 150

13. Replication, Transcription and Translation 159

14. Vitamins 173

15. Minerals 189

16. Water, electrolytes and acid –base balance 199

17. Nutrition and Energy Metabolism 205

18. Hormones 211

19. Organ function Tests 219

20. Xenobiotics 225

21. Cancer 229


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CHAPTER - 1 | Cell Membrane & Transport

1. Describe common structural and functional features of eukaryotic cell.

A . 1. Though mammals contain many types of cells which differ in function, shape, size

etc., they have common features.

2. All types of cells contain nucleus, membrane and sub cellular components etc.

3. Each cell component has uniqe structure and function.

Nucleus

1. It is located in the centre of most of the cells. It is surrounded by double layered membrane

in which pores are present.

2. Pores present in the membrane permits exchange of material between nucleus and other

structures of cell.

3. The outer membrane of nucleus is continuous with other membrane.

4. Chromosomes are present in the nucleus of human and other mammalian cells.

5. Chromatin is the substance present in chromosomes.

6. Chromatin is nucleoprotein which consist of DNA and proteins.

7. Nucleus also contain some amount of RNA.

8. DNA and RNA present in nucleus are carriers of genetic information.

Chapter

Mitochondria:

1. Like nucleus it is also surrounded by double layered membrane.

2. The inner membrane forms folds which are named as cristae.

3. Knob like structures are present in cristae.

4. Matrix is the name given to space within inner membrane.

Cell Membrane & Transport 1

001

Outer Nuclear Membrane

ChromosomeInnerNuclear Membrane

Nuclear Pore

NUCLEUS


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Endoplasmic reticulum: This membranous net work is divided into smooth endoplasmicreticulum and rough endoplasmic reticulum.

Smooth endoplasmic reticulum: It is also

known as microsomal fraction of cell. It appears

smooth due to the absence of ribosomes. It is

site of hydroxylation reactions of drugs and

steroids etc.

Rough endoplasmic reticulum : It is

continuation of outer nuclear membrane. It

appears rough due to presence of ribosomes. It

is the site of protein synthesis.

Golgi complex : It is another membranous net

work present in cell. It is involved in secretion

of proteins, formation of other cellular

components and in glycosylation of proteins.

5. Number of mitochondria varies from one organ to other.

6. Mitochondria is the power house of the cell.

7. Size and shape of mitochondria depends on the function of organ in which they are present.

8. Electron transport chain, citric acid cycle, β-oxidation, ketone body formation, pyruvate

oxidation, few of heme biosynthesis and urea cycle enzymes are present in mitochondria.

MITOCHONDRIA

Outer

MembraneChistaeKnob

Inner Membrane

Matrix

Smooth

Endoplasmic

Reticulum

Nucleus

RibosomeNucleus

Rough Endoplasmic Reticulum

Golgi

Complex

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Lysosomes: They are vesicle like membrane surrounded structure present in cytoplasm. They are

involved in hydrolysis of internalized foreign molecules as well as endogenous substances. Since

lysosomes are involved in the removal of endogenous substances they are called as suicide bags of

cell.

Peroxisomes: Are membranous vesicles found in cytosol. They are involved in hydrogen peroxide

metabolism.

Cytosol: Soluble portion of the cell is called as cytosol. It contains enzymes of glycolysis, HMP

shunt, aminoacid and fatty acid activation, fattyacid synthesis, and few enzymes of porphyrins

and urea synthesis.

2. Write note on chemical constituents of cell.

A. Chemical constituents of life forms (Cells):Cells contain various organic as well as

inorganic molecules and water.

a. Organic substances : They form major part of cell. There are two type of organic

molecules. Macro molecules are nucleic acids, proteins, lipids and carbohydrates.

Amino acids, fatty acids, peptides, vitamins, monosaccharides, nucleotides, hormones

and coenzymes are small organic molecules.

b. Inorganic molecules : They are present as anions and cations. They are sodium,

potassium, calcium, magnesium, bicarbonate, chloride, phosphate etc.

c. Water: It is the most predominant molecule of cell.

3. Write about structure of cell membrane.

A. 1. Membranes are non covalent assemblies of lipids and proteins with carbohydrates

attached.

2. They are gel or semi fluid or semi solid structures.

3. Membrane lipids are organized in a bilayer form in which proteins are embeded. 4.

The two sides of membrane are different i. e. molecular composition of cytosolic side

of membrane differs from extra cellular side.

Membrane lipids :

1. Lipids present in membrane are

phospholipids, cholesterol and glycolipids.

2. Phosphalipids and glycolipids form

membrane bilayer.

3. The proportion of phospholipid and

glycolipid in membrane is different in

membranes.

4. Membrane lipids are in constant motion.

P R O T E I N

Protein

Membrane

Bilayer

Cytosol

Lipid

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Membrane proteins:

1. There are two types of membrane proteins.

2. They are peripheral membrane proteins and integral membrane proteins.

3. The protein content is different in membranes.

4. The peripheral membrane proteins are present on membrane surface.

5. The integral membrane proteins occupy membrane bilayer.

Fluid mosaic model:

1. It is model proposed for membrane structure.

2. Membrane is of fluid in nature.

3. Lipids forms bilayer.

4. The membrane proteins float in the lipid bilayer.

5. Membrane proteins interact extensively with lipids present in bilayer.6. Surface of the membrane appears as that of mosaic surface.

4. Describe transport of molecules across cell membrane with examples.

A. For the trans port of molecules across membrane several mechanisms exist.

Membrane transport: Two or more types of transport mechanism are involved in

movement of molecules across membrane.

They are A. Simple or passive diffusion B. Mediated transport

A. Simple diffusion: It is transport of molecules down the concentration gradiant. It

does not require either energy or carrier.

Examples : Absorption of xylose and mannose.

B. 1. Facilitated or mediated transport: This type of transport requires carrier molecule.

The carrier molecule is responsible for moving molecules from out side of cell to in

side or vice versa. It does not require energy.

Mechanism of transport of molecules by carrier involves conformational change in carrier

molecule. The carrier molecule exist in two states and has binding site for solute molecule. In

the native state the binding site of carrier molecule is exposed to high concentration of solute.

Proteins

Lipid Bilayer

Mosaic Surface

Protein

Fluid Mosaic Model

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The solute molecule binds to carrier molecule at its binding site. This is followed by

conformational change in the carrier molecule which exposes solute to low concentration.

Solute molecule is released and carrier molecule comes back to native state.

Examples: 1. Glucose uptake by adipocytes, erythrocytes

2. Fatty acid uptake by enterocytes

3. Transport of glucose from enterocyte into blood

2. Active transport: It transport solute molecules against concentration gradient i. e. from low

concentration to high concentration. It is accompanied by hydrolysis of ATP.

+ +Examples: 1. Na /K – ATPase

2+2. Ca -ATPase of muscle.

+ +3. H /K -ATPase of stomach.

3. Secondary active transport: In this type of transport energy required for movement of

solute molecule is derived from movement of another solute molecule down concentration

gradient. Hence it is called as cotransport. Carrier is symporter.

Examples: 1. Glucose uptake by enterocyte

2. Aminoacid uptake by enterocyte

5. Define ionophores and ion channels. Give examples.

A . Ionophores: Ionophores form pores in membrane which allows movement of ions across

membranes.

Examples: 1. Gramicidin. 2. Valinomycin. 3. Diphtheria toxin.

Ion channels: Ion channels are pores (channels) present in membrane that allow

movement of ions across membrane.

+ + 2+Examples : 1. Sodium (Na ) channel. 2. Pottasium (K ) channel. 3. Calcium (Ca ) channel.

- 4. Cholirde (Cl )channel.

6. Write differences between facilitated transport and active transport.

A. Differences between facilitated transport and active transport:

005

Solute

Outside

Membrane

inside

Binding Site

Conformational

Change

Carrier


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Facilitated transport Active transport

1. Transport molecules down the concentration 1. Transport molecules against gradient.

concentration gradient.2. Requires no energy. 2. Requires energy.

3. Carrier is saturated 3. No carrier saturation.

4. Influenced by hormones 4. Not under hormonal influence.

7. What are the functions of cell membrane?

A . 1. Membranes separates cell from its surroundings.

2. Shape of cell depends on membrane.

3. Cell interacts with environment through the membrane.

4. Membranes act as permeability barriers.

5. Membranes are involved in energy production.

6. Flow of molecules form cell into surroundings and vice versa is regulated by

membranes.

7. Formation of various cell organelles requires membrane.

Other model questions are

8. Write note on mitochondria structure and functions.

9. Write briefly on nucleus/ nucleolus.

10. Write about cytomembranes of a eukaryotic cell.

11. Define facilitated transport and active transport. Give examples

for each.

12. Write about membrane lipids and membrane proteins.

13. Explain features of fluid mosaic membrane model with help of a

diagram

14. Facilitated transport.

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CHAPTER - 2 | Carbohydrates

1. Classify carbohydrates. Give examples for each class. Add note on the

function of each example.

A. Carbohydrates classification: Carbohydrates are classified intoa. Monosaccharides.

b. Oligo saccharides,

c. Polysaccharides based on their carbon chain length.

Monosaccharides:

1. Monosaccharides are carbohydrates which

can not be hydrolyzed to small molecules.

2. Monosaccharide containing three to seven

carbons with functional aldehyde or ketogroup are present in nature.

3. They are aldotriose, keto triose, aldo tetrose,

keto tetrose, aldopentose, ketopentose,

aldohexose, ketohexose and aldoheptose, ketoheptose.

4. Glyceraldehyde and dihydroxy acetone are aldotriose and ketotriose respectively. The

phosphorylated forms are metabolic intermediates.

5. Erythrose is an example for aldotetrose and erythrulose is an example for ketotetrose.

Erythrose phosphate is metabolic intermediate.

6. Aldopentose and ketopentose are ribose and

ribulose respectively. Ribose is constituent of

nucleic acids. Ribulosephosphate is metabolic

intermediate.

7. Aldohexoses are glucose, galactose and mannose.

Fructose and sedoheptulose are ketohexose and

ketoheptose respectively.

8. Glucose is present in our blood and gives rise to

energy on oxidation.

Glyceraldehyde Dihydroxy Acetone

H – C O

H – C – OH

CH OH2

CH OH2

C O

CH OH2

FructoseGlucose

CHO

H – C – OH

CH OH2

HO – C – H

H – C – OH

H – C – OH

CH OH2

C – O

CH OH2

HO – C – H

H – C – OH

H – C – OH

Chapter

2Carbohydrates

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9. Galactose is a constituent of lactose and has function like glucose.

10. Phosphorylated sedoheptulose is metabolic intermediate.

Oligosaccharides : They consist of few monosaccharides.

They are disaccharides, trisaccharide etc.

Monosaccharide Monosaccharide

Glycosidic Bond

Disaccharide

Monosaccharide Monosaccharide Monosaccharide

Tri Saccharide

Glycosidic Bond

Disaccharides:

1. Disaccharide consist of two monosaccharide units.

2. Glycosidic bond joins individual monosaccharides. Maltose, lactose and sucrose are examples.

Name Composition Linkage Source

Lactose Glucose+ Glucose α (1→4) Malt, barley

Maltose Glucose+Galactose β (1→ 4) Milk

Sucrose Glucose+Fructose α, β (1→ 2) Sugarcane, honey, fruit juices.

Functions: All disaccharides yields energy after their hydrolysis to constituent

monosaccharides.

Polysaccharides:

1. Polysaccharides are made up of more than ten monosaccharide units.

2. They are polymers of monosaccharides.

3. They are divided into

a. Homopolysaccharides

b. Heteropolysaccharides.

Homopolysaccharides:

1. They are made up of only one type of monosaccharide.

2. So building block of homopolysaccharide is only one type.

3. They are glycogen, starch, cellulose, inulin, dextrin etc.

Starch:

1. It consist of two components. A major amylose and minor amylopectin components.

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2. Amylose is a linear polymer of glucose in which monomeric glucose units are joined by α (1, 4)

linkages. It has helical secondary structure.

3. Amylopectin has branched structure.

4. In the linear part glucose units are joined by α (1, 4) linkage. At the branch point glucose units

are held by α (1→6) linkage.

5. For every 20-30 glucose units a branch point is present in amylopectin.

6. The secondary structure of amylopectin is random coil due to branches.

7. Starch is common polysaccharide in our diet. It is a storage polysaccharide present in our food

stuffs like rice, wheat, pulses, tubers, grains etc.

Glycogen:

1. The structure of glycogen is like that of amylopectin part of starch.

2. Glucose units are held by α (1→4) likages in straight chain part and at branch point α (1→6)

glycosidic bond is present between glucose units.

3. Though the glycogen structure is similar to amylopectin the number of branch points are

more.

4. Branching occurs for every 6 glucose units.

Glu Glu Glu Glu Glu Glu Glu Glu Glu Glu Glu Glu Glu Glu Glu Glu

a (1Z 4)

Glycosidic Bond

Glu

Glu

Glu

Glu

a (1Z 4)

Glycosidic Bond

a (1Z 6)

Glycosidic Bond

AMYLOPECTIN

Glycogen

a (1Z4) linkage

a (1Z6) linkage

Glu-Glucose

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5. It is present in humans and other mammals.

6. It is also known as animal starch because in animals it serve as reserve food or stored material

7. It is present in liver and skeletal muscle in more amounts.

Heteropolysaccharides:

1. They are made up of more than one type of monosaccharide.

2. Usually a disaccharide which is made up of more than one type of monosaccharide serve as

building block or repeating unit.

3. Hyaluronicacid, heparin, chondroitin sulfate, keratan sulfate etc. are examples for

heteropolysaccharides.

4. Their composition and functions are given below.

Name Composition Functions

1. Hyaluronicacid - ( — β-glucuronicacid- Lubricant in synovial fluid

N-acetylglucosamine-) and in eye.n

2. Chondroitinsulfate – ( – β- glucuronicacid-N- acetyl Structural component of

Glucuronicacid sulfate-) — bone, tendon and cartilagen

3. Heparin – (–Iduronicacid- glucosamine sulfate – Anti coagulant

Glucuronicacid – glucoosamine sulfate-) – n

4. Dermatan sulfete – (– Iduronicacid- N-acetyl Component of bone & skin

Galactosamine sulfate–) – n

5. Keratan sulfate – (– galactose-N-acetyl Components of cartilage &

Galactosamine sulfate-) – loose connective tissuen

2. Define carbohydrates. Write their biological functions.

A . Carbohydrates are defined as poly hydroxy alcohols with functional aldehyde or keto

group.

Functions:

1. They are major energy source for man.2. They function as reserve food material in man and plants.

3. They are components of connective tissues, bone, cartilage, skin, membrane and

nerve tissue.

4. They are components of blood group substances, nucleic acids etc.

5. Carbohydrate derivatives are vitamins, antibiotics and drugs

3. Define enantiomers or optical isomers. Give examples.

A . Enantiomers (optical isomers): Optical isomers of a compound are called as enantiomers. D

and L glucose are examples for optical isomers.

–

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4. Define epimers and anomers. Give examples.

A . Epimers:

nd rd th1. They differ in the configuration of –OH and H groups on 2 , 3 and 4 carbon atoms of

monosaccharide.

2. Glucose and galactose are epimers.

3. They differ in the configuration of –OH and H groups on fourth carbon atom.

4. Like wise glucose and mannose.

Anomers:

1. Anomers differ in configuration of –OH and-H groups on first or anomeric carbon of sugar.

2. α –glucose and β – glucose are two anomers of glucose.

3. In α- glucose –OH is present on right side whereas in β –glucose it is present on left side.

5. Write note on mutarotation.

A . Mutarotation:

1. Due to the presence of asymmetric carbon glucose exhibits optical activity and

rotates plane polarized light.

◦2. Optical rotation of a solution containing α –D-glucose is +112 .

◦3. But on standing the rotation decreases and reaches +52. 5 and no more change

occurs due to equilibrium.

4. β –D-glucose also exhibits this change in optical rotation when allowed to stand in a

solution.

◦ ◦5. This compound initially show +19 of rotation and it gradually increases to +52. 5 .

6. This phenomenon is called as mutarotation.

7. It is due to change of glucose form pyranose ring form to open chain form.

α-D-Glucose ↔ D –Glucose ↔ β-D- Glucose◦ ◦ ◦

+120 +52. 5 +19

Pyranose ring form Open chain form Pyranose ring form.

6. Write briefly about paper chromatography.

A. 1. It is most widely used separation technique.

2. It is used for the separation of closely related compounds from mixture.

3. It is based on partition principle of the compounds to be separated between two phases.

4. The mixture to be separated is applied on whatman No:1 filter paper over a short

distance from one end.

5. The paper serve as support for stationary phase of solvent system.

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6. The solvent system consist of n-butanol, aceticacid and water in the ratio of 4:1:5.

7. The paper is dipped in the solvent system and solvent is allowed to flow over applied

sample.

8. The water is absorbed by filter paper and serve as stationary phase.

9. The organic solvent that moves over the paper is known as mobile phase.

10. Compounds which are more soluble in organic solvent move faster.

11. The relative mobility of the compounds during chromatography depends on the

partition coefficients of the compounds in two solvent phases.

12. So similar compounds which have different partion coefficients move to different

extents.

13. The ratio of the distance moved by compound to the distance moved by solvent is

known as R values.f

14. R values are different for different solvent systems.f

15. Compounds are identified by staining.

16. Aniline or silver nitrate are used to stain

carbohydrates after separation.

17. Among carbohydrates glucose moves faster followed by

galactose.

18. Paper chromatography is also used for separation of

amino acids.


7. Write a note on monosaccharides.

8. Define disaccharides. Give examples.

9. How sucrose and maltose differ with respect to a. Structure b.

Source c. Function

10. Write briefly about structure and functions of starch and glycogen.

11. What are polysaccharides? Classify. Give examples.

12. Write briefly about mucopolysaccharides

13. Write four functions of carbohydrates.

14. Write composition and functions of a. Hyaluronicacid b. Heparin.

15. Write composition and function of lactose.

Sample Application

Galactose

Glucose Fructose

Solvent Front

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CHAPTER - 3 | Proteins, Plasma Proteins, Peptides & Aminoacids

PROTEINS

1. Classify proteins based on composition giving examples for each class.

A. Proteins classification, based on composition. According to this proteins are

classification into

a. Simple proteins.

b. Conjugated proteins.

c. Derived proteins.

a. Simple proteins:Are those proteins which yields only aminoacids on hydrolysis.

Ex:Trypsin, plasma albumin, pepsin etc.

b. Conjugated proteins:

1. Are those proteins that yields aminoacids and other organic or inorganic molecules

or non protein molecules on hydrolysis.

2. The non protein molecule is called as prosthetic group.

3. Usually conjugated proteins are named according to the name of non protein.

4. Some examples are tabulated below.

Conjugated protein Non protein part Examples

1. Heme proteins Heme Hemoglobin

2. Glycoproteins Carbohydrate Immunoglobulins

3. Flavoproteins FMN or FAD Succinate dehydrogenase

4. Nucleoproteins Nucleicacid Chromatin

5. Phosphoproteins Phosphorus Casein

6. Lipoporteins Lipids Various classes of lipoproteins

like VLDL, HDL

7. Metalloproteins Metals Cytochromes

c. Derived Proteins: Are those proteins that are derived from partial hydrolysis of

simple or conjugated proteins. Gelatin, Peptone and proteose are examples.

Proteins, Plasma Proteins, Peptides & Aminoacids

Chapter

3

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2. Classify proteins on the basis of solubility giving examples for

each class.

A . Classification of proteins based on their solubility. According to this proteins are

classified intoa. Albumins.

b. Globulins.

c. Glutelins.

d. Protamins.

e. Histones.

f. Prolamines.

g. Sclero proteins.

a. Albumins:Are those proteins that are soluble in water as well as salt solutions. Egg

albumin, plasma albumin and lactalbumin are examples.

b. Globulins: Are proteins weakly soluble in water but soluble in salt solutions.

Ovoglobulins, plasma globulin and lactoglobulins are examples.

c. Glutelins: Are proteins soluble in mild acids and alkalis. zein, glutenin and oryzenin

are examples.

d. Protamines: Are proteins soluble in water and ammonia. Fish proteins like salmine and

sturine are examples.

e. Histones: Are those proteins which are soluble in water and dilute acids. Histones

present in chromosomes are examples.

f. Prolamines:Are proteins insoluble in water and alcohol but soluble in dilute alcohol.

Plant proteins zein and gliadin are examples.

g. Sclero Proteins: Are proteins insoluble in water, acids and alkalis. Animal proteins

keratin, elastin and collagen are examples.

3. Describe structural organization of proteins.

OR

What is primary, secondary, tertiary and qua ternary structure of proteins?

Explain each one giving examples. .

A. Primary structure of proteins :

1. Aminoacid sequence of a protein is known as primary structure of protein.

2. Peptide bonds and disulfide bonds are involved in primary structure.

H N2 COOH Ala Gly Phe Tyr His Leu Val Gly Lys Leu

Ala - Alanine

Gly - Glycine

Phe - Phenyl Alanine

Lys - Lysine

Peptide BondTyr - Tyrosine

His - Histidine

Val - Valine

Leu - Leucine

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e. There are 3. 6 aminoacids in one turn of α-helix.

f. Peptide bonds that are four aminoacid residues away participate in hydrogen bonding

i. e. -N-H of second aminoacid residue and –C=O of sixth aminoacids are involved in

hydrogen bonding.

g. α-helix of fibrous proteins is right handed.

h. α-helix is destabilized by hydrophobic aminoacids.

I. In contrast aromatic aminoacids stabilizes α-helix.

j. α-helical regions are found in several other proteins.

Beta (β)Pleated Sheet

When two or more polypeptide chains line side by side along long axis beta pleated sheet is

formed. Adjacent segments of a protein or polypeptide chain may also form secondary

structure.

Structural features of β-Pleated Sheeta. Polypeptide chains are fully extended along long axis in beta pleated sheet.

b. Inter chain hydrogen bonds stabilizes beta pleated sheet.

c. Based on direction β-pleated sheet is divided into i. Antiparallel β-pleated sheet and ii.

Parallel β-pleated sheet.

d. In antiparallel β-pleated sheet polypeptide chains run in opposite direction.

e. In parallel β-pleated sheet polypeptide chains run in same direction.

f. Pleated sheet is found in many proteins. Albumin and hemoglobin of blood contains β-

pleated sheet.

g. Antiparallel β pleated sheet is found in β-Keratin of silk fibroin, spider web and amyloid

protein found in the brain of Alzheimer's disease patients.

h. β-pleated sheet content varies among proteins.

Tertiary structure of protein:

1. It is formed due to three dimentional folding of polypeptide chain of protein in space.

2. Tertiary structure of protein contains ordered and disordered secondry structures i.

e. α-Helix, β-pleated sheet, random coil conformation etc.

Beta Pleated Sheet (Parallel)

Polypeptide Chain 2

Polypeptide Chain 1

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Forces involved in maintenance:

1. Several non covalent bonds stabilizes tertiary structure.

2. Usually it refers to native conformation of a protein.

3. Internal hydrogen bonds, electrostatic, hydrophobic and van der Waals interactionsare bonds that keep tertiary structure intact.

4. In the case of proteins that are made up of only one polypeptide chain tertiary structure

is the final level of protein structure.

Quaternary structure of protein:

1. Proteins which are made up of more than one polypeptide chain contains quaternary

structure.

2 . Such proteins are known as oligomeric proteins and constituent polypeptide chains are

referred as sub units or protomers.

Hemoglobin, creatine phosphokinase. Lactate dehydrogenase etc are examples for

proteins with quaternary structure. Hemoglobin and lactate dehydrogenase are made

up of four subunits whereas creatine phosphokinase contains two sub units.

4. Define proteins. Write their functions.

A. Proteins are polymers of aminoacids. The aminoacids are joined by peptide bonds.

Hence they are also called as polypeptides.

Functions of Proteins:

1. Proteins are present in body. They are structural components of tissues, cells etc.

2. Proteins function as hormones

3. Proteins functions as enzymes

4. Proteins regulate gene expression.

5. Proteins are involved in muscle contraction

Amino Acid1 Amino Acid2 Amino Acid3 Amino Acid4 Amino Acidn

Peptide Bond Protein (Polypeptide)

COOH

NH2Tertiary

Structure

Sub Unit

Quaternary Structure

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6. Proteins perform transport functions.

8. Proteins are used as nutrients.

7. Proteins act as buffers.

9. Proteins act as reservoir of minerals

10. Proteins act as infective agents.

5. Classify proteins based on their shape.

A . Protein classification on the basis of shape. According to this proteins are divided into a.

Fibrous proteins b. Globular proteins.

a. Fibrous Proteins: Are proteins in which polypeptide chains are elongated. Keratin,

collagen and elastin are examples.

b. Globular Proteins: Are proteins in which polypeptide chains are folded into globular

or spherical shape. Hemoglobin, albumin and trypsin are examples.

6. Write briefly about protein denaturation.

A . 1. Denaturation of protein is loss of native conformation.

2. Denatured proteins exhibit properties which are not shown by native protein.

3. They are

A. Loss of biological function.

B. Solubility changes.

C. Susceptible to enzyme action.

D. Increased chemical reactivity.

E. Dissociation of subunits in case of oligomeric protein.

Methods of protein denaturation

By several ways proteins are denatured. They are

H1. By exposing protein to extreme acidic or alkaline P . 2. High temperature. 3. Use of

detergents like sodium dodecyl sulfate (SDS). 4. By treating with strong acids like

trichloroacetic acid (TCA), Tungstic acid and picric acid. 5. Exposing to ultraviolet

light. 6. Using salts like urea and guanidinium chloride at high concentration. 7.

Vigorous shaking. 8. Ultrasonication. 9. Heavy metal exposure like lead, arsenic,

mercury etc. 10. By organic solvents like acetone, alcohol etc.

Protein

Heat

Denatured Protein

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Clinical Importance:

1. Protein denaturation is part of estimation of blood constituents.

2. Plasme protein separation involves protein denaturation.

3. Isolation of protein or enzyme from mixture of proteins involves denaturation.

Examples for protein denaturetion:

1. Exposure of egg albumin to high temperature leads to formation of coagulum.

2. Sweet tasting protein monellin loses its property on denaturation.

7. Write methods for determination of protein primary structure.

A . Primary structure of protein is determined by

a. Sanger's method.

b. Edman's method.

Sanger's method:

1. In this 1-fluoro-2, 4-dinitrobenzene (FDNB) is used to determine primary structure of

protein.

2 . FDNB reacts with free aminogroup of protein to produce yellow 2, 4 – dinitrophenyl

residue of aminoacids which are identified after chromatographic separation.

3 . Since FDNB reacts with other amino acids only one aminoacid is determined at a time with

this method

Edman's meathod:

1. In this method also primary structure is elucidated from N-terminus.

2. However complete sequence of protein is obtained by repeating several times with

Edman's reagent.

3. Unlike Sanger's method Edman's reagent reacts with only one aminoacid and rest of theaminoacids remain intact.

4. Edman's reagent (Phenylisothiocyanate)reacts with free aminogroup in presene of acid to

produce phenylthiohydantoins which are estimated by using chromatography.

PLASMA PROTEINS

8. Describe composition and functions of various plasma proteins.

A . Several structurally and functionally different proteins are present in plasma. They are

albumin and various components (fractions) of globulins.

FDNB + Protein

Identification of

amino Acid

Dinitrophenyl Derivative

Chromatography

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Albumin: It contributes osmotic pressure in blood. It is involved in maintenance of blood

volume. One gm of albumin can hold 18ml of fluid in blood. It is involved in transport of several

substances. Further it binds to various substances and drugs. Fatty acids and bilirubin are

transported by albumin. Several hormones also transported by albumin Sex hormones and

glucocorticoids are transported by albumin. Albumin function as buffer. Peripheral tissues

use albumin as nutrient.

Alpha, (α ) alpha (α ), beta (β)and gamma ( g) globulins are components of globulin fraction of1 2 2

plasma. Further each of subglobulin fraction consist of several proteins.

α -globulins1

α -antitrypsin and α -acid glycoprotein are principle components of this fraction. Other1 1

components are α-lipoprotein, prothrombin, α -fetoprotein, thyroxine binding and retinol1

binding proteins.

α -antitrypsin: It accounts for more than 90% of α-globulin fraction. It is an inhibitor of trypsin,1

chymotrypsin, elastase etc. It prevents action of proteases on pulmonary tissue and other

tissues. Lack of α -antitrypsin results in emphysema.1

α-Lipoprotein: It is involved in transport of lipid (cholesterol)from peripheral tissues to liver

for removal.

Prothrombin: It is one of the blood clotting factors and involved in blood coagulation.

α -fetoprotein:As the name implies it is the protein present in foetal blood and its presence in1

adult blood indicates liver cancer. It is considered as tumor marker for liver cancer. Thyroxine

and retinol binding proteins are involved in the transport of thyroxine and vit. A respectively.

α -globulins: α -macroglobulin, haptoglobulin, erythropoietin, ceruloplasmin and pseudo2 2

choline esterase are present in this fraction.

α -Macroglobulin: It is an inhibitor of proteases. It combines with proteases to form complex2

which is then easily removed from circulation.

Haptoglobulin: It is involved in the transport of hemoglobin. It combines with hemoglobin to

from complex.

Erythropoietin: It is required for formation of reticulocytes.

Ceruloplasmin: It is also known as ferrooxidase. It is a copper containing protein.

Pseudo choline estrase: It is an enzyme present in blood.

β-globulins

β-lipoprotein, transferrin and complement-3 are components of this fraction.

β-Lipoprotein : It is involved in the transport of lipids from liver to peripheral tissues.

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Transferrin: It is involved in the transport of iron.

Complement-3 :It is one of the component of complement system.

γ-globulins

Immunoglobulins are major component of this fraction. C-reactive protein is anothercomponent of this plasma protein fraction.

C-Reactive protein: It is produced in inflammatory condition.

Immunoglobulins

They are involved in defence function. They are antibodies present in serum. They are

produced when foreign molecules or antigens enters inside body.

Structure:

1. Generally an Immunoglobulin is made up of 4 polypeptide chains. The molecular weight

of this is about 150000 daltons.

2. Two types of polypeptide chains are present. Two heavy or H chains and two light or L

chains.

3. Each H chain molecular weight is 50, 000 and contains 450 aminoacids.

4. Molecular weight of L chain is about 25, 000 and contains 220 aminoacids.

5. The H chains contains variable region at N terminus [V ] and three constant regions atH

C terminus [C C and C ].H1, H2 H3

6. In the L chain one variable region (V ) at N terminus and constant region (C ) at CL L

terminus exist.

7. The aminoacid sequence varies in variable regions of H and L chains and largely

depends on class or type of immunoglobulin.

8. However constant regions of H and L chain aminoacid sequence is constant or same in

various types of immunoglobulins

9. The variable regions recognizes antigens.

Shape

1. Overall shape of immunoglobulin is that of Y.

2. Two H chains intertwines to form base of Y.

3. Arm of the Y is formed by joining L chains to H chains.

4. Most of the immunoglobulins contains carbohydrate in C region.H2

5. Several intra and inter chain disulfide bonds maintain Y shape.

Classification: Based on composition of H and L chains

immunoglobulins are classified into three major classes and two

minor classes. I G,I A and I M are major classes. I and I E are minorg g g g g

classes. Not only composition, size, shape, distribution and function

021

–S-S– Light

Chain

Heavy

Chain

IMMUNOGLOBULIN


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also varies among various classes of immunoglobulins. Each class of immunoglobulin contains

unique H chain based on which they are named. The different H chains are g (Gamma), α

(Alpha), μ (mu), δ (Delta) and ε (Epsilon). However in all five classes of immunoglobulins only

two types of L chains are found. They are κ (kappa) and λ (lambda).

1. Ig G Class

Structure : It consist of two g type H chains and two

L chains of K or lambda type. So it is designated as

g L or g K or g λ2 2 2 2 2 2.

Function: It is major immunoglobulin of serum. It is

the major antibody of new born. Ig G binds to foreign

cells or antigens which increases their susceptibility

for elimination.

2. IgA Class

Structure: It consist of two alpha type H chains and two κ or λ type L chains. Hence it is

designated as α L It may exist as multimer of the basic unit. Polypeptide chains like SC2 2.

and J are also found. They are involved in joining of monomers.

Function: It accounts about 10-20% of immunoglobulins. It is chief of antibody of mucosal

cells, secretions of lungs and gut where it combines with antigen thus protecting them from

harmful antigens.

3. Ig M Class

Structure: It consist of two μ type H chains and two L

chains. Hence it is designated as μ L . This basic unit2 2

exist as multimer like Ig A class. Most common

occurence is in the pentameric form (μ L ) . SC and J2 2 5

components also may occur.

Function: Ig M on B- Lymphocytes act as receptor for

antigens. Complement fixation requires Ig M. About 5

– 10% total immunoglobulins is Ig M type.

4. Ig D Class

Structure: It is made up of two δ type H chains and two C chains. It is designated as δ L2 2.

Function: It is involved in alternate pathway of complement fixation. It accounts only 0.

5% of total immunoglobulins.

5. Ig E Class

Structure: It is made up of two ε type H chains and two L chains. It is designated as ε L2 2.

Ig G dimer

1

2

1

2

34

5

Ig M Pentamer

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Tripeptide : It is composed of three aminoacids. Two peptides bonds connect these

aminoacids. Glutathione and thyrotrophin releasing hormone are examples.

Pentapeptide : Five aminoacids are linked by four peptide bonds. Enkaphains are examples.

13. Write the glutathione composition, short form and functions.

A. Glutathione : It consist of glutamate, cysteine and glycine. It is written as glutamate-

cysteine- glycine. G-SH is short form. It is a reducing agent. It undergo dimerization on loss

of hydrogen. G –S-S-G is oxidized form. It is involved in the maintenance of -SH groups on

proteins on reduced form. In red blood cells (R. B. C.) it is involved in the elimination of

hydrogen peroxide. It participates in detoxification. It is involved in hormone secretion and

apoptosis.

14. Define cyclic peptide and toxic peptide. Give examples.

A. Cyclic peptide (s):It is formed when amino and carboxyl terminals of the peptide are joined

by peptide bond. Antibiotic gramicidin –S and tyrocidin are examples.

Toxic peptides: Are peptides acting as toxins. α-Amanitin is toxic peptide present in mush

rooms which is responsible for mush room poisoning.

AMINOACIDS

15. Classify aminoacids based on side chain and ring structure giving

examples.

A . Aminoacids are classified into seven major classes based on side chains.

a ) Aliphatic aminoacid s: Are those which contain aliphatic side chains. Glycine, alanine,

valine, leucine and isoleucine are examples for aliphatic aminoacids. The latter three

aminoacids are also known as branched chain aminoacids.

H|

H N – C – COOH2|H

Glycine

H|

H N – C – COOH2|

CH3

Alanine

H|


CH

CH CH3 3

Valine

H|


CH2|

CH

CH CH3 3

Leucine

AminoAcid1

Dipeptide Peptide Bond

AminoAcid2

AminoAcid1

Tripeptide Peptide Bond

AminoAcid2 AminoAcid3

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g ) Iminoacids: Are those aminoacids in which amino group is replaced by imino group.

They are proline and hydroxy praline.

16. Define an aminoacid. Write their functions.

A . Aminoacids are acids containing aminogroups. They are building blocks of proteins andpeptides present in humans and other living organisms.

Functions: Free aminoacids are found in blood and cells of humans. Hormones, purines,pyrimidines, heme, some vitamins, creatine etc found in body are derived from aminoacids.

17. Classify aminoacids based on reaction in solution.

H|

H N – C – COOH2|R

Amino Acid

Acid Group Amino Group R-Side Chain

f) Aromatic aminoacids : Aromatic rings are present in the side chains of these

aminoacids. They are phenylalanine, tyrosine and tryptophan.

NH

NH

COOHProline

COOH

Hydroxy Proline

OH

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A. Semi essential aminoacids: Semi essential aminoacids are synthesized in the body to some

extent. They are histidine and arginine.

Unusual or rare aminoacids or Non protein aminoacids: These aminoacids are not found in

proteins. But they have other functions. Examples are i). Intermediates of urea cycle i. e.

ornithine. citrulline and argininosuccinate. ii). taurine. iii). Gamma aminobutyric acid(GABA). iv). Beta (β)-alanine. v). Pantothenic acid.

20. Explain charge or acid base properties of aminoacids.H

A . 1. Depending on p of surroundings an aminoacid can exist as cation or positively charged

molecule, anion or negatively charged molecule and zwitter ions.

2. Zwitter ion carries no net charge It contains equal number of positive charges and

negative charges.

3. Further aminoacids act as acids or bases. When alkali is added aminoacid act as acid by

donating proton. Aminoacid act as base by accepting a proton from acid.H

4. At nutral p aminoacid functional groups amino and carboxyl groups exist in ionizedform.

+5. The amino group exist in protonated -NH form and carboxyl group in the dissociated3

- –COO form this is known as zwitter ionic form.

6. In strong acidic conditions –COOH remains undissociated i. e. aminoacid exist as

cation.

+7. In strong alkaline condition proton from –NH is lost i. e. aminoacid exist as anion.3

Anion ← Zwitterion → cationH H H

AlkalineP Neutral P acidicP

H8. The P dependence of charge of aminoacid is used for separation of aminoacids.

21. Define isoelectric point of aminoacid. How it is determined?

Write its importance.

A . 1. At iso electric point aminoacid exist as zwitter ion.

2. The isoelectric point of an aminoacid having one carboxyl group and one amino group isk

obtained by dividing P values of these groups with 2.

3. At isoelectric point aminoacids or proteins have minimum solubility.

4. This is exploited for separation of proteins or aminoacids from mixture.

k .22. Define P values of amino acid. Write the significance of it.

H A . 1. It is P at which un dissociated and dissociated forms of a group are present in equal

H|

– H N – C – COO2

|

R

+ H -|

– H N – C – COO3

|

R

+ H|


R

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amounts.k kam. H

2. For example P of amino group of aminoacid is designated as P It is P at which+

dissociated (-NH ) and undissociated (-NH ) are found in equal amounts.2 3k ka.

3. Like wise P of acid groups of aminoacid is designated as P

k4. The P values indicates strength of groups.k k

5. Low P values indicates more ionizing power. High P values indicates less ionizing power.


23. Write a note on immunoglobulins.

24. Write briefly about conjugated proteins.

25. What are derived proteins ? Give examples.

26. What is meant by secondary structure of proteins? Give examples.

27. Write about quaternary structure of proteins giving examples.

28. Write about structural feature of α –helix.

29. Write a note on ß -pleated sheet.

30. Draw general structure of immunoglobulins. Label its parts.

31. Write briefly about Ig E and Ig M.

32. Write briefly about tertiary structure of protein.

33. Define primary structure of protein. Write a method for its determination.

34. Write a note on albumin.

35. Write very briefly about aromatic aminoacids.

36. Write note on α - globulins.1

37. Write clinical importance of alpha fetoprotein and macroglobulin.

38. Name sulphur containing aminoacids and basic aminoacids.

39. Classify immunoglobulins. Give structural and functional aspect of each class.

40. Name three charged forms of aminoacid. When the aminoacid assumes these states?

41. Write a note on α - globulins.2

42. Write a note on ß-globulins.

43. Write a note on the general structure of immunoglobulins.

44. Non protein aminoacids

45. Protein structure

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CHAPTER - 4 | Lipids

1. Classify lipids. Give examples for each class along with functions.

A . Classification: Based on composition lipids are classified into

I. Simple lipids

II. Compound lipids and

III. Derived lipids.

I. Simple lipids : Esters of fatty acids with alcohol are known as simple lipids. Fats and

waxes are simple lipids.

a. Fats:

1. Are esters of fatty acids with glycerol.

2. Triglycerides, diglycerides and mono glycerides are fats.

3. Triglyceride is also called as tri acyl glyccrol.

4. In triglycerides three fatty acids are esterified to three hydroxyl groups of glycerol.

5. In diglycerides two of the hydroxyl groups of glycerol are esterified with glycerol.

6. Only one fatty acid is esterified to any one of hydroxyl group of glycerol in

monoglycerides.

Functions:

1. They are mainly involved in storage function.

2. Adipose tissue present under skin contains triglycerides. In the abdomen, thighs and in

mammary gland, adipose tissue containing triglycerides is present.

CH – OH2 |CH – OH

|CH – OH2

CH – O – COR2 1 |CH – O – COR2

|CH – O – COR2 3

CH – O – COR2 1 |CH – O – COR2

|CH – OH2

CH – O – COR2 1 |CH – OH

|CH – OH2

Glycerol Triglyceride Diglyceride Monoglyceride

COR , COR , COR - Acyl Groups1 2 3

Esterbond

Lipids

Chapter

4

029


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3. Obese people contain more triglycerides.

4. Women contain more triglycerides than men.

5. In hibernating animals, seals and penguins triglycerides are more.

6. Fat under the skin has dual roles. It function as energy store as well as insulatoragainst cold.

b. Waxes: Are esters of fatty acids with long chain alcohols. Wool and bees wax are waxes

known well. Wool is ester of fatty acid with long chain alcohol lanosterol and agnosterol.

Bees wax is an ester of fatty acid with myricyl alcohol.

Functions:

1. Waxes form protective layer over the skin, fur, feathers of animals. Shiny appearance

of fruits, leaves of plants are due to waxes.

2. Waxes are hard at low temperature and soft at high temperature.

3. Wool a wax of animal origin is used as protection against low temperature or cold.

Woolen clothing protect us from cold for this reason.

4. Waxes act as water barrier for animal, plants, birds etc.

II. Compound lipids: Are esters of fatty acids with alcohol containing additional groups

and nitrogenous bases. They are further subdivided based on alcohol present. They are

glycerophospho lipids and sphingolipids. In glycero phospholipids glycerol is alcohol

and sphingosine is alcohol in sphingolipids.

A. Glycerophospholipids:

1. In which two fatty acids are esterified to two hydroxyl groups and nitrogenous base

bearing phosphate is esteri fied to third hydroxyl group of glycerol.

2. Glycerophospholipid lacking nitrogenous base is known as phosphatidicacid.

3. Some glycerophospholipids are considered as derivatives of phosphatidic acid and they

are named accordingly.

4. Phosphatidyl choline, phosphatidyl serine, phosphoatidyl ethanolamine and

phosphatidyl inositol are examples for glycerophospholipids.

5. Due to the presence of phosphate they are often referred as phospholipids.

i) Phosphatidyl choline: It consist of glycerol, two fatty acids esterified to first and

second hydroxyl groups. Phosphate is esterified to third hydroxyl group.

Nitrogenous base choline is esterified to phosphate. Lecithin is the alternate name

for this glycerophospholipid.

ii) Phosphatidyl serine : It is an aminophospholipid. Serine an aminoacid is attached to

phosphate which is esterified to third hydroxyl of glycerol. First and second

hydroxyl groups of glycerol are esterified with two fatty acids. Cephalin is alternate

name for this phospholipid.


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Cerebrosides:

a. They consist of sphingosine, fatty acid and carbohydrate or sugar.

b. Usually they are named according to sugar present.

c. For example if glucose is the sugar present in a cerebroside then it is called asglucocerebroside.

d. Similarly galacto cerebroside contain galactose sugar.

e. In some cerebrosides sulfate is esterified to sugar moiety.

f. They are known as sulfatides or sulfolipids.

Cerebroside Fatty acid Sphingosine Sugar

Sulfolipid Fatty acid Sphingosine Sugar Sulfate

Gangliosides:

a. They are most complex of all compound lipids.

b. They are made up of sphingosine, fattyacid, oligosaccharide and sialic acid.

c. The oligo saccharides contain aminosugar and acetylated aminosugars.

Ganglioside Fattyacid Sphingosine Oligosaccharide Sialicacid

Functions:

1. White matter of the brain and myelin sheath of nerves contain cerebrosides.

2. Grey matter contain gangliosides.

3. Gangliosides serve as receptors for toxins, hormones etc.4. Cerebrosides and gangliosides are also present in non neural tissues.

5. Gangliosides are also involved in cell cell recognition, growth and differentiation

and carcinogenesis.

III Derived lipids : Hydrolysis of simple and compound lipids produce derived lipids. Fatty

acids, steroids, fat soluble vitamins and glycerol are examples for derived lipids.

Fatty acids : Hydrolysis of triglycerides yield fatty acids. They are acids containing

long hydrocarbon chain. Many fatty acids are identified in nature. They are subdivided

into

a. Saturated fatty acids.

b. Unsaturated fatty acids based on nature of hydrocarbon chain.

a. Saturated fatty acids:

1. The hydrocarbon chain of these fatty acids is saturated.

2. No double bonds occur.

3. Saturated fatty acids containing up to 20 carbons are identified.

4. More important are palmitic acid, stearic acid and arachidonic acids.


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b. Unsaturated fatty acids:

1. They contain double bonds in hydrocarbon chain.

2. Unsaturated fatty acids containing up to 30 carbons are identified.

3. They are subdivided into mono unsaturated fatty acids and polyunsaturated

fatty acids (PUFA) based on number of double bonds.

4. Mono unsaturated fatty acids are palmitoleic acid and oleic acid. They

contain one double bond.

5. Poly unsaturated fatty acids are linoleic, linolinic and arachidonic acids.

They contain many double bonds.

CH – CH – CH – CH – – – – – – CH – COOH3 2 2 2 2

Hydro Carbon Chain Acid Group

Saturated Fatty Acid

CH – CH – – – – CH = CH – CH – – – – CH = CH – – – – CH – COOH3 2 2 2

Double Bond

Unsaturated Fatty Acid

Functions:

1. Fatty acids are source of energy for humans like glucose.2. Fatty acids are components of nervous tissue, lipoproteins etc.

3. Poly unsaturated fatty acids are essential fatty acids.

4. They are required for the synthesis of eicosanoids.

5. They are also components of cell membrane.

Steroids : They contain complex fused ring system which is also known as steroid nucleus.

Fused ring system contains four rings collectively known as cyclopentanoperhydrophenan

threne ring.

Cholesterol is an example for steroid which is steroid alcohol.

Functions :

1. It is most abundant steroid in animals.

2. About 200g of cholesterol is present in human adult.

3. Nervous tissue is rich in cholesterol.

4. Egg yolk is also rich in cholesterol.

5. Cholesterol is used for the formation of vitamins

and steroid hormones.

6. Vit. D is derivative of cholesterol. HO Cholesterol

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7. Glucocorticids, mineralo corticoids, male sex hormones, female sex hormones are

derivatives of cholesterol.

2. Define lipids. Write briefly about their functions.

A . Lipids are organic substances soluble only in organic solvents like chloroform, ether and

benzene but insoluble in water.

Functions:

1. Lipids are structural components of cell membrane and nervous tissue.

2. Lipids present in myelinated nerves act as insulators for propagation of

depolarization wave.

3. Lipids present under skin act as thermal insulator against cold.

4. Lipids are energy source for man like carbohydrates.

5. Lipids like steroids function as hormones.

6. Lipids present around kidney act as padding and protect kidney from mechanical

injuries.

7. Lipids serve as vitamins.

8. Lipids are part of lipoproteins present in blood plasma.

9. Absorption of fat soluble vitamins requires lipids.

10. Essential fatty acids a kind of lipids are essential for life.

11. Lipids act as microbicides and fungicides.

12. Some lipids function as surfactants.13. Lipids are involved in immune response.

14. Lipids act as mitogens.

15. Some lipids serve as precursors for the formation of complex lipids.

16. Due to its high energy and water output on oxidation mammals including humans

prefer to store energy in the form of lipid only

3. Write a note on structure and function of lyso phospholipids.

A . Partial hydrolysis of glycerophospholipids yield lysophospholipids. Hence they contain

only one acyl group instead of two acyl groups and phosphorylated nitrogenous base.

Functions : They are produced as intermediates during phospholipid biosynthesis. Lyso

lecithin a derivative of lecithin is present in cobra venom. It is a strong hemolysing agent.

4. Write a note on plasmalogens.

A . They are also glycerophospholipids. They contain unsaturated fatty alcohol in the place of

first fatty acid at first hydroxyl group. Because of this an ether linkage is found on first

carbon instead of usual ester linkage. Phosphorylated nitrogenous bases are usually

choline, serine, ethanolamine etc.

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Functions:

1. They are structural components of tissues like brain, muscle and heart.

2. Platelet activating factor is a plasmalogen.

3. In cancer cells plasmalogen content is more.

5. Write a note on dipalmitoyl lecithin.

A . 1. It consist of two palmitic acid residues esterified to first and second carbon atoms of

glycerol and phosphocholine on third carbon.

2. In the lung it serve as surfactant.

3. It is involved in the maintenance of shape of alveoli of lungs.

4. It is synthesized only after 30 weeks of gestation.

5. Hence its deficiency occurs in premature infants and causes respiratory distress

syndrome (RDS).

6. Write the composition and clinical importance of Cardiolipin.

A. 1. Cardiolipin is a double phosphoglycerolipid.

2. Two phosphatidic acids are esterified to first and third carbons of glycerol.

3. It is structural component of inner mitochondrial membrane.

4. It shows immunological properties.

5. It is found in cardiac muscle hence the name.

6. It is useful in the diagnosis of syphilis.

7. What are lipoproteins ? Write their composition and general structure.

A . 1. Lipoproteins are lipid and protein complexes present in plasma.

2. The protein part of lipoprotein is called as apolipoprotein or apoprotein.

3. Non covalent bonds keep lipid and apoprotein together.

Composotion:

1. Triglycerides, free and esterified cholesterol and phospholipids are major lipids

present in lipoproteins.

2. However proportions of these lipids in various classes of lipoproteins differs.

3. Composition of apoprotein differs among lipoproteins.

4. Also proportions of proteins in various classes of

lipoproteins differs.

5. Five types of apoproteins are known so far.

6. They are apoprotein A, or apo A, apoB, apoC, apoD,

and apo E. ApoF, apoG and apo H are also found.

7. Some of them has subtypes also.

8. ApoB is largest of all.

035

Lipoprotein

Apoprotein

Lipids

CORE


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Structure:

1. Lipoproteins have spherical to oval shaped structure.

2. Non polar hydrophobic lipids lies in the central core.

3. They are surrounded by more polar hydrophilic apolipo proteins and lipids.

4. The outer polar coat solubilizes inner non polar lipids in aqueous environment of

plasma.

8. Write separation, classification and functions of lipoproteins.

A. Separation and classification:

1. Lipoproteins are separated by ultracentrifugation and electrophoresis.

2. Ultra centrifugation separates lipoproteins based on their density.

3. Density of a lipoprotein is inversely related to lipid content.

4. So higher the lipid content of lipoprotein then lower its density.

5. Ultracentrifugation separates lipoproteins into 4 classes.

6. They are1. Chylomicrons. 2. Very low density lipoproteins (VLDL). 3. Low density

lipoproteins (LDL) and 4. High density lipoproteins (HDL).

7. Electrophoretic separation of lipoproteins is based on differences in mobilities.

8. The plasma lipoprotein electrophoresis gives four bands which corresponds to

chylomicrons, α-lipoprotein, preβ-lipoprotein and β-lipoprotein.

LDL

Chylomicrons b-Lipo

Protein

VLDL

Pre

Lipo Protein

b

HDL

a-Lipo

Protein

Lipoprotein

Electrophore sis

Functions:

1. Chylomicrons are involved in the transport of dietary triglycerides from intestine to

liver.

2. Very low density lipoproteins (VLDL)are involved in the transport of endogenous

triglycerides from liver to peripheral tissues.

3. Low density lipoproteins (LDL) are involved in the transport of cholesterol from liver to

peripheral tissues.

4. High density lipoproteins (HDL) are involved in the transport of cholesterol form

peripheral tissues to liver.

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5. Some apoproteins have functions other than structure. They act as activators or

inhibitors of enzymes of lipid metabolism.

9. What are prostaglandins? Name them. Write their functions.

A . Prostaglandins (PG) are derived from prostanoic acid. It is a cyclic compound with two sidechains. The cyclic ring is cyclopentane ring. Many types of prostaglandins are found. They

differ in substituent groups on cyclo pentane ring. Some known prostaglandins are PGA,

PGB, PGC, PGD, PGE, PGF, PGG and PGH.

Functions:

1. Prostaglandins have several effects on cardiovascular system.

a. They act on heart and increases cardiac output and myocardial contraction.

b. They are involved in maintenance of arterial pressure and vascular tone.

c. Some prostaglandins act as antihypertensive agents. They lowers blood pressure.

2. Prostaglandins act on central nervous system. They are involved in sedation and

tranquilizing effect in cerebral cortex.

3. Prostaglandins influences excretory functions of kidneys. They facilitates elimination

of sodium, potassium and chloride ions. They also influences urine volume.

4. Prostaglandins act on respiratory system.

a. They dilates bronchi. b. They act as anti asthmatics. c. They relieve nasal

congestion.

5. Prostaglandins act on digestive system.

a. They decrease acid secretion in stomach.

b. They are useful in peptic ulcer treatment.

6. Prostaglandins have actions on reproductive system.a. They cause contraction of uterine muscle.

b. They are useful in inducing abortions.

c. They have role in fertility.

7. Prostaglandins play role in metabolism. Through cAMP they mediate their action.

cAMP level alteration affects lipid as well as carbohydrate metabolism.

8. Some prostaglandins are involved in inflammation.

9. Haematopoietic system also influenced by prostaglandins.

a. They inhibit platelet aggregation.

Cyclo

Pentane

Ring

COOH

CH3

Sidechain 1

Sidechain 2

Prostanoic Acid

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b. Some promote clot formation.

c. Some cause platelet aggregation.

10. Prostaglandins promotes tooth movement by increasing resorption.

10. Define micelles, mixed micelles and Liposome and lipid bilayer. Write the importance of each one.

A. These liquid structures are generated by amphipathic molecules which contain both

hydrophobic as well as hydrophilic parts.

Micelles : Are formed when amphipathic molecules are present beyond critical

concentration in aqueous medium. They are sphere shaped aggregates of amphipathic

molecules. Bile salts form micelles which are required for lipid digestion.

Mixed micelles: Are formed when micelles of one type of lipids combines with other lipids.

In the intestine bile salt micelles combines with products of lipid digestion to form mixed

micelles. Mixed micelle formation is essential for digestion and absorption of lipids.

Liposome: Is formed when a lipid bilayer cyclizes i. e. two ends of lipid bilayer joins. They

are used as carriers of drugs or genes in case of gene therapy.

Lipid bilayer:Is formed when phospholipids are present in water and oil mixture. Cell

membrane is a lipid bilayer.


11. Write briefly about triglycerides.

12. Write the importance of cholesterol.

13. What are glycerophospholipids? Give examples. Mention their functions.

14. Write a note on phospholipids.

15. Write the composition and function of sphingomyelin.

16. What are glycolipids? Give examples.

17. Write composition and function of gangliosides.

18. What are derived lipids? Give examples.

19. Classify fatty acids. Give examples for each class.

20. Write the functions of prostaglandins.

21. Essential fatty acids.

22. Eicosanoids

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CHAPTER - 5 | Enzymes

1. Classify enzymes. Give examples for each class along with reaction

and cofactors involved.

A . Classification: Based on the type of reaction they catalyzes enzymes are classified into

six major classes. All classes of enzymes with examples are given below.

1. Oxidoreductases: They oxidizes or reduces substrates using an hydrogen acceptor or

donor.

Glutamate dehydrogenase is an example which catalyzes below given reaction.+

Glutamate+ NAD+H O→ α-ketoglutarate +NADH+H + NH2 4.

Succinate dehydrogenase that catalyzes below given reaction is another example.

Succinate +FAD→Fumarate + FADH2.

2. Transferases: They transfer group between substrates.Transaminase catalyze transfer of amino group from one aminoacid to ketoacid as shown

below.

Alanine+ α-Ketoglutarate→ Pyruvate + Glutamate

Glucokinase catalyses transfer of phosphate from ATP to glucose as shown

Glucose +ATP→ Glucose-6-phosphate + ADP.

3. Hydrolases: These enzymes hydrolyzes glycosidic bond or ester bonds etc.

Amylase catalyzes hydrolysis of glycosidic bonds of starch. Amylase

Starch +H O Hydrolytic products.2

Pepsin catalyzes hydrolysis of peptide bonds of proteins

Pepsin

Protein+H O Hydrolytic products.2

4. Lyases:They catalyzes splitting of substrates by using mechanism other then hydrolysis

and generates double bonds in products HMG- CoA lyase is an example.

Enzymes

Chapter

5

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HMG-CoA lyase

HMG-CoA Acetoacetate+Acetyl-CoA.

Citrate lyase is another example.

Citrate+ ATP+CoA →

Oxaloacetate +Acetyl-CoA+ADP+Pi

5. Isomerases: They catalyzes formation of functional, optical and geometrical isomers.

Phosphohexose isomerase inter converts functional isomers.

Glucose-6- phosphate→Fructose -6-phosphate.

Maleyl acetoacetate cis-trans isomerase catalyzes inter conversion of geometric isomers.

Maleyl acetoacetate→ Fumaryl acetoacetate.

6. Ligases:These enzymes catalyzes formation of new compounds by linking two compounds

using energy.

Arginino succinate synthase is an example.

Citrulline+ Aspartate+ ATP→ Argininosuccinate+ AMP+PPi

Propionyl –CoA carboxylase is another example.

Propionyl-CoA+CO + ATP→D-Methyl malonyl- CoA+ADP+P2 i

2. Define enzymes. Write an enzymatic reaction and properties of

enzymes.

A . Enzymes are biological catalysts. They fasten the chemical reactions in living

organisms.

An enzyme catalyzed reaction consist of substrate, enzyme and product. Substrate is

substance on which enzyme act.

Substrate Enzyme Product.

Enzyme properties:

Enzymes are proteins and they are not consumed in the reaction. Enzymes are usually

high molecular weight substance. Molecular weight of enzymes ranges form thousands to

millions. Enzymes are able to cut big molecules to small molecules. Conversely enzymes

form big molecules by joining small molecules. Enzymes are more efficient than man made

catalysts and they have enoromous power of catalysis.

3. Explain how enzymes accelerate reactions in living organisms?

A . 1. Enzymes accelerate reactions like that of catalyst because enzymes are catalysts.

2. The acceleration of reaction by catalyst is explained with transition state theory.

3. When enough energy is supplied reactant of a reaction is converted to product.


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4. It involves formation of transition

state of reactant.

5. Usually transition state is unstable so

reactant get converted to stable

product.

6. In presence of catalyst reactant

attains transition state much easily

and requires less energy. 7. In

presence of enzymes transition state

is attained very rapidly and requires

very less energy.

8. The amount of energy required by reactant to attain transition state is known as

activation energy.

9. Thus enzymes accelerate reactions by lowering activation energy.

4. Write about nomenclature and EC number of enzymes.

A . Enzyme name consist of two parts. The first part indicates substrate name the second part

ends with “ase” and indicates type of reaction enzyme catalyzes.

EC Numbre : It is a enzyme code number given to an enzyme. It has four digits. The first

digit indicates major class, second digit indicates sub class, third digit refers to sub

subclass and final digit indicates specific enzyme.

5. Define active site of enzyme. Write its characteristics.

A. Active site: It is part of the enzyme that is needed for enzyme action or catalysis.

Characteristics of active site: It has two parts.

a. Catalytic site : Part of active site that brings about catalysis.

b. Binding site : Part of active site that binds to

substrate. Aminoacids that makes active site are far

away in the absence of substrate. In the presence of

substrate active site aminoacid that are apart comesclosely and orient in specific manner to form precise

active site. Active site is three dimentional and are

clefts within enzyme molecule. Serine, histidine,

aspartate, cysteine, glutamate etc usually make up

active site.

6. Write about active site models of an enzyme.

A . Two models are proposed for active site of enzyme.

C

T

I

V

T

I

O

N

E

N

E

R

G

Y

A CTI V

A TION ENERG Y

TransitionState

Ground State

Uncatalyzed

Non Enzymecatalyzed

EnzymeCatalyzed

Progress of ReactionO

Binding Site

Catalytic Site

E

N

Z

Y

M

E

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1. Lock and key model: As the name implies shape of the active site and substrate are

complementary like that of lock and key in this model. Complementary nature of active

site and substrate shape allows formation of tight enzyme substrate complex to yield

product and free enzyme. However this model fails to explain reversible enzyme

catalyzed reactions due to rigid shape of active site.

2. Induced fit model: In this model rigid nature of active site is avoided. Enzyme active

site is flexible in this model. Further in the absence of substrate active site is not in

proper form. Binding of substrate to enzyme induces conformational change in enzyme

molecule. As a result precise active site forms to favour tight binding between enzyme

and substrate and catalysis. Since enzyme is unstable in induced conformation it

returns to native state in the absence of substrate. This model allows formation of

enzyme product complex to favour the formation of substrate in the case of reversible

enzyme catalyzed reactions.

Enzyme Product

Active

site

Enzyme (E) Substrate (S) (ES) Complex

+ +

7. Explain influence of various factors on enzyme catalyzed reactionwith suitable diagrams and examples.

A . Enzyme catalyzed reactions are affected by many factors.

They are

1. Substrate concentration.

2. Temparature

3. Hydrogen ion concentration.

4. Enzyme concentration.

5. Cofactors and inhibitors.

Enzyme Product

Active

site

Enzyme (E) Substrate (S) (ES) Complex

+ +


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1. Substrate concentration: Initial velocity (V ) of enzyme reaction increasesO

proportionately in the beginning with increasing substrate concentration (S). Further

increase in substrate concentration leads to slight increase in initial velocity and

reaches maximum (V ). Beyond that increase in substrate concentration has no effectmax

on velocity of enzyme reaction. The plot of (S) versus V is a rectangular hyperbola. It isO

known as Michaleis plot.

Michaleis-Menton Equation:It is mathematical expression for Michalies plot relating

substrate concentration, initial velocity and maximum velocity.

V (S)max V = Where K = Michaleis constant.O m

K + (S)m

From this equation Michaleis constant is obtained. From Michaleis plot substrate

concentration that produces maximum velocity is difficult to obtain. But at least

substrate concentration that produces half maximal velocity is possible to know. So by

substituting this in Michaleis – Menton equation we get.

V V (S)max max=

2 K + (S)m

On cross multiplication

K +2 (S)=S i. e. K = (S).m m

Michaleis constant: It is substrate concentration that produces half maximal velocity.

K significance:m

a. Measurment of enzyme activity requires knowledge of K . It provides substratem

concentration range for proper measurement of enzyme activity.

b. K indicates affinity of enzyme towards substrate. K and affinity are inversely related.m m

High K indicates low affinity and low K indicates high affinity.m m

c. K values of enzyme are needed for use as drugs and reagents.m

Vmax

Vmax2

Vo

O K m (S)

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2. Temperature: Enzymes work optimally at a particular temperature. Above or below that

temperature enzyme exhibits low activity.

Optimum Temperature: It is temperature at which enzymes are optimally active. For most of

the enzymes. Optimum temperature is temperature of cell where it exist. Hence optimum◦

temperature for most of the mammalian enzymes is 37 C.

Enzyme activity increases as temperature is increased until optimum temperature is reached.

Beyond that enzyme activity decreases with increasing temperature. Plot of enzyme activity

versus temperature is bell shaped curve. Some of plant derived enzymes and enzymes of

thermophilic bacteria have optimum temperature close to boiling point.

100

Enzyme Activity

50

0 37

Temperature (°C)

70

Optimum

Temperature

100

Enzyme Activity

50

0 7PH

14

OptimumH

P

H3. Hydrogen ion concentration: Like optimum temperature enzymes requires a particular P for

H Hoptimum activity. This is known as optimum P . For most of the enzymes optimum P rangesH H

from 5-8 or P of body or cell in which it occurs. However enzymes with alkaline optimumP orH H

acidic optimum P are known. When P and enzyme activity are plotted a bell shaped curve is

obtained.

4. Enzyme concentration : The rate of product formation in an enzyme catalyzed reaction is

proportional to concentration of enzyme. The plot of enzyme concentration and rate of product

formation is straight line passing through origin.

5. i. Inhibitors: These substances if present in enzyme catalyzed reaction they inactivate

enzyme. As a result rate of product formation may decrease or not occur.

ii. Cofactors: Several enzymes can work only in presence of some non protein molecules. In

the absence of these molecules enzyme catalysis may be slowed down or not take place.

COMPETITIVE INHIBITION

1. It is a kind of reversible enzyme inhibition.

2. It occurs in presence of competitive inhibitor.

3. The competitive inhibitor is structurally similar to the substrate. Hence it competes with

substrate to bind at active site.


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4. Binding of inhibitor at active site blocks formation of product.

5. By increasing substrate concentration this type of enzyme inhibition is masked.

6. In presence of competitive inhibitor K of an enzyme increases i. e, affinity decreases. Howeverm

V is not altered.max

7. The interaction of enzyme inhibitor and substrate is shown as equation below.

E+S ES E +P I = Inhibitor

E+I EI X E+P P = Product

Example: Classical example for competitive inhibition is inhibition of succinate

dehydrogenase by Malonate which is structurally related to substrate succinate.

Vmax

Vmax2

Vo

O K m (S)

Substrate

Only

Inpresence of

competitive

inhibitor

K m

Substrate

Competitive

Inhibitor

Competitive Inhibition

Applications

Competitive inhibitors are used in medicine as 1) Antibiotics, 2). Anti cancer agents 3). Drugs for

treating metabolic diseases.

Antibiotics : Competitive inhibitors used as antibiotics to treat bacterial infections are mainly

sulfonamides or sulfa drugs. Most of these drugs contains sulfanilamide an analogue of p- amino

benzoic acid. For growth bacteria need vitamin folic acid. p- amino benzoic acid is required for

formation of folic acid. Sulfonilamide competitively inhibit enzyme involved in synthesis of folic

acid using p- amino benzoic acid. This results in block in folic acid formation. Lack of folic acid

leads to arrest of bacterial growth.

COOH

|CH2|

CH2|

COOH

Succinate + FAD

Succinate

Dehydrogenase

COOH

|

CH2|

COOH

Malonate

(-)

Fumarate + FADH2

Competitive

Inhibtor

(-) Inhibition

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Anti cancer agents: Several competitive inhibitors are used as anti cancer agents. Folic acid

analogs are most notable among them. Rapidly growing cancer cells requires folicacid for nucleic

acid formation. Dihydrofolate reductase is competitively inhibited by folic acid analogs like

aminopterin and amethopterin. They are used in the treatment of blood cancer. Inhibition ofdihydrofolate reductase results in block in folic acid formation. This in turn affect nucleic acid

synthesis. Lack of nucleic acids leads to arrest of cancer growth.

þ-Amino benzoic Acid + Precursor

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