Biomolecules

Synopsis

Living bodies are built up with biomolecules.

The sequence that relates biomolecules to living organism is as follows.

Biomolecules → organelles → cells → Tissues → organs → living

organism

Some important biomolecules are carbohydrates, proteins, nucleic

acids, lipids, vitamins and hormones.

Cell-energy-Photosynthesis

The basic structural and functional unit of living organism is the "cell".

Molecules like those of glucose undergo oxidation by means of

enzymes and liberate energy.

The reaction which has Gibb's energy change (Δ G) greater than zero

is called endergonic reactions.

The reaction which has Gibbs energy change $$(\Delta G) less than

zero is called exergonic reactions.

Ex :- Some metabolic processes (ΔG>0) in human body take place by

coupling with the exergonic reaction like the conversion of ATP to ADP.

The process, in which the green parts of plants absorb sunlight to

prepare glucose and oxygen from CO2 and H2O is called photo

synthesis.

6CO2+6H2O+2880KJ−→−−−−SunlightC6H12O6+6O2

Depending on the nature of plants and the reaction type, glucose is

converted to disaccharides and polysaccharides like starch,cellulose

(or) proteins (or) oils.

Photosynthesis takes place in the presence of light followed by dark

reaction which does not need light.

Here, ATP undergoes hydrolysis and carries the dark reaction with the

energy liberated from its hydrolysis.

ATP−→−−−−−−31kJ/molADP−→−−−−−−31kJ/molAMP−→−−−−−−14kJ/molA

The following reaction takes place in the respiration process where

animals and plants release energy.

C2H12O6+36ADP+36H3PO4+6O2→6CO2+36ATP+42H2O

Carbohydrates

Classification

General formula Cn(H2O)m

They can be better described as optically active polyhydroxy

aldehydes (or) ketones (or) the compounds which yield them on

hydrolysis.

Most of them are similar to sugar in taste, and hence they are also

known as Saccharides.

( Latin word for sugar is saccharum)

Monosaccharides

These cannot be hydrolysed to simple compounds.

Depending upon the total number of carbon atoms in

monosaccharides and on nature of functional groups present

(aldehyde or ketone), the terms for their classification are as follows:

No. of

Term

Carbon Atoms

Aldose

General

Ketose

3 Triose Aldotriose Keto triose

4 Tetrose Aldotetrose Keto tetrose

5 Pentose Aldopentose Keto pentose

6 Hexose Aldohexose Keto hexose

Disaccharides

Disaccharide: A disaccharide on hydrolysis gives 2 monosaccharide

units

Ex:- Sucrose, Maltose and Lactose

Oligosaccharides

These undergo hydrolysis and yield 3 to 10 monosaccharide units.

Example: A disaccharide on hydrolysis gives two simple

monosaccharide units.

C12H22O11+H2O−→−H+C6H12O6+C6H12O6

Polysaccharides

These undergo hydrolysis and give more than 10 monosaccharide units.

Example:Starch and cellulose-General fomula (C6H10O5)n

(C6H10O5)n+nH2O−→−−−−−303k,H+2−3atmnC6H12O6

Preparation of glucose

Glucose is known as dextrose because it occurs in nature as the

optically active dextro rotatory isomer.

Glucose is prepared in the laboratory by acid hydrolysis of cane sugar

in alcoholic solution.

C12H22O11+H2O−→−H+C6H12O6+C6H12O6

Sucrose Glucose Fructose

It is obtained in large scale by the hydrolysis of starch with dil. H2SO4(or)

HCl at 2-3 atm pressure & 393 K temp.

Properties & structure elucidation of glucose

Molecular formula of glucose is experimentally found as C6H12O6

Acylation of Glucose with acetic anhydride gives glucose penta

acetate. Hence, Glucose molecule contains 5 'OH' groups

Glucose reacts with NH2OH and one molecule of HCN and forms

monoxime and cyanohydrin respectively. These reactions suggest the

presence of one carbonyl group.

Glucose reduces Tollen's reagent to metallic silver and also reduces

Fehling's solution to reddish brown cuprous oxide and itself gets oxidised

to gluconic acid. These reactions suggest that the carbonyl group is an

aldehydic group.

On oxidation with HNO3 both glucose and gluconic acid form

saccharic acid, a dicarboxylic acid. It suggests the presence of

primary alcoholic group (−CH2OH) Glucose on prolonged heating with HI gives n-hexane. It suggests the

linear arrangement of all the 6 carbon atom in glucose.

D-Glucose on reaction with excess of phenyl hydrazine ( 3 moles of

phenyl hydrazine per mole of glucose), forms a dihydrazone known

as osazone.

Properties and Structure Elucidation of glucose

With dil. NaOH solution, glucose under

goes reversible isomerisation and gives a mixture of D-mannose and D-

fructose. This reaction is known asLobry de Bruyn-Van

Ekenstein rearrangement.

Cyclic Structure of glucose

The open chain structure of Glucose proposed by Baeyer explained

most of its properties. But it could not explain the following.

Glucose does not give schiff's test and does not react

with NaHSO3and NH3, inspite of presence of -CHO group

Pentacetate of glucose does not react with −NH2OH group indicating

absence of -CHO group

Mutarotation of glucose

When glucose was

crystallised from a concentrated solution at 30oC, it gives α - form with

melting point 146oC and [α]D=+111o. But glucose crystallised from a

hot saturated aqueous solution at a temperature greater than 98oC,

given β-form with a melting point 150oC and [α]D=+19.2o. These two

forms of glucose differ in the stereochemistry at C-1 These

two α and β forms, when separately dissolved in water and allowed to

stand, their specific rotation gradually change and reach to a specific

constant value 52.5o. This spontaneous change in specific rotations of

an optically active compound is called mutarotation.

Alpha and Beta glucose

The one with OH group on the right side is known as α−D-Glucose and

that with -OH group on the left asβ−D −glucose. The two forms are not

mirror images of each other that are not super imposable hence are

not enantiomers. The groups projected to the right in Fischer projection

are written below the plane of the ring in Howarth structure and those

on the left are written above the plane of the ring.

The α and β forms are confirmed by the reaction of glucose, with

methanol in the presence of dry HCl to give methyl α−D - Glucoside

and methyl β-D- Glucoside.

Fructose

Fructose is a ketohexose. It is also called Laevalose and fruit sugar.

Preparation

C12H22O11+H2O→C6H12O6+C6H12O6

Sucrose Glucose Fructose

Structure of fructose

It has the molecular formula C6H12O6.

Its chemical properties suggest that if C-2 is C=O group and all six

carbons in a straight chain similar to glucose open chain structure.

It is laevorotatory compound and belongs to D-series. D-(-) fructose. Its

structure is

To explain all of fructose properties it is suggested with two cyclic

structures

i.e. α−D−(−)−fructofuranose and β−D−(−)−fructofuranose.

The stereochemistry of all sugars is determined with respect to D-or L-

glyceraldehyde.

Oligosaccharides

The disaccharides are composed of 2 molecules of monosaccharides.

These on hydrolysis with dil acids(or) enzymes yield two molecules of

either the same (or) different monosaccharides.

C12H22O11−→−−H3O+C6H12O6+C6H12O6

In disaccharides, the two mono- saccharides are joined together by

glycosidic linkage(-O-)

A glycoside bond is formed when hydroxy group of the hemiacetal

carbon of one monosaccharide condenses with a hydroxy group of

another monosachharide, to give -O-bond.

Surcose

It is the most

common disaccharide present in plants. It is non reducing.

It's obtained mainly from sugarcane (or) beetroot.

It is dextro rotatory, [α]D=+66.5o.

Even though sucrose is a dextro rotatory, on hydrolysis with

dil.acids(or)enzyme invertase, it gives equimolar mixture of dextro

rotatory glucose and laevo rotatory fructose.

As the laevo rotation of fructose (−92.4o) is more than dextrorotation of

glucose (+52.5o), the mixture is laevorotatory.

In the hydrolysis of sucrose there is a change in the sign of rotation from

'd' to 'l'. This change is known as inversion and the mixture is

called invert sugar.

1. α−D Glucose and β−D fructose units are linked through α,β-

glycosidic linkage between C-1 of α−D−Glucose and C-2

of β−D−fructose.

2. Glucose unit is in pyranose and fructose unit is in furanose form.

Maltose

It's obtained by partial hydrolysis of starch by diastase enzyme present

in Malt.

2(C6H10O5)n+nH2O−→−−−−DiastasenC12H22O11

Starch Maltose

It's a reducing sugar.

On hydrolysis, one mole of maltose yields 2 moles of D-Glucose.

The two α-D-glucose units in maltose are linked through a α -Glycosidic

linkage between C-1 of one unit and the C -4 of another.

Both the glucose units are in pyranose form.

Lactose

Lactose occurs in milk and also called as milk sugar.

Hydrolysis of Lactose with dil acid yields equimolar mixture of D-Glucose

and D-Galactose.

It's a reducing sugar

The hydrolysis occurs in presence of enzyme emulsin.

Polysaccharides

Carbohydrates containing large number of monosaccharide units

joined through glycosidic linkages are called polysaccharides.

They have general formula (C6H10O5)n

Ex : Starch, cellulose, dextrin, glycogen etc.

Starch

Starch is a white amorphous powder with no taste or smell. It is almost

insoluble in cold water,but relatively more soluble in boiling water.

Starch is easily hydrolysed in saliva by an enzyme amylase.

Its solution gives blue colour with iodine solution in cold but the colour

disappears on heating

On hydrolysis it forms D-glucose.

When treated with enzyme, diastase, it yields maltose.

2(C6H10O5)+nH2O→nC12H22O11

Starch Maltose

Starch is not oxidised by Tollen's reagent or Fehling's solution and it does

not form osazone. These facts indicate that hemiacetal hydroxy groups

of glucose units at c-1 are in glycosidicform.

Glycosides are acetals in which the anomeric hydroxy group has been

replaced by an alkoxy group.

Glycosides are carbohydrate derivatives obtained by the replacement

of anomeric -OH by some of the substituent and are termed -O, N-, S-,

glycosides etc, depending on the atom attached to the anomeric

carbon.

Starch is a mixture of two polysaccharides. (i)Amylose (ii)Amylopectin.

Natural starch contains 10-20% of amylose and 90-80% of amylopectin.

Cellulose

Cellulose is formed in the photo synthesis process.

It is a polysaccharide composed of large number β- D-glucose,units

joined by β(1,4) glycosidic linkages.

In the hydrolysis of cellulose finally, D-glucose is formed.

Cellulose is a colourless amorphous solid. It is mainly linear and its

individual strands align with each other through H-bonds,because of

which it becomes rigid and cell wall material.

It does not reduce Tollen's reagent (or) Fehling's solution and does not

form osazone.

Glycogen

The carbohydrates are stored in animal bodies as glycogen.

It is also called animal starch because its structure is similar to

amylopectin.

It is present in liver, muscles, and brain.

It is also present in yeast and fungi.

Amino acids

Synopsis

1. Amino acids are organic compounds

containing both amino group (−NH2) and carboxylic acid (-COOH) i.e.

they are di-functional.

2. The bond between two amino acid molecules is peptide bond or

amide bond, and the resultant is known as di-peptide.

3. The peptide chain extended to three amino acid molecules is tri-

peptide and extended to four amino acid molecules in tetra-peptide,

and soon.

4. The peptide chains with less than 50 amino acids are usually called

Poly peptides and the polypeptides that contain more than 50 amino

acid units are proteins.

5. Depending on the location of the amino group on carbon chain,

that contains the carboxylic acid functional group, amino acids are

classified as ,b,g and d etc.

6. The amino acids, which can not be synthesized,in the body but can

only be supplied to the body through diet, are called essential

amino acids.They are valine, Leucine, Isoleucine, Arginine, Lysine,

Threonine, Methionine, Phenylalanine,Tyrptophan and Histidine.

7. The amino acids, which are synthesized in the body, are known as

non essential aminoacids.

8. The general formula of α -amino acids is

9. Though there are more than 700 different amino acids that occur

naturally, only 20 of them are important in the formation of proteins.

10. All these 20 amino acids are amino acids. And all of them except

proline contain primary amino group.

11. Proline is a secondary amine

Side chains

Amino acids exist as zwitter ion, showing acidic

character due to group N+H3 and basic character due

to COO− group.

Amino acids with non polar side chain are :

1. Glycine H Gly G

2. Analine - CH3 Ala A

3. Valine −CH(CH3)2 Val V

4. Leucine −CH2−CH(CH3)2 len L

5. Iso Leucine -CH−CH2−CH3 Ile I

6. Phenylalanine -CH2−C6H5 Phe F

7. Proline

3

Side Chains

Amino acids

with acidic side chain are :

If -COOH groups are more it is acidic.

1. Glutamic acid -CH2−CH2−COOH Glu E

2. Aspartic acid -CH2−COOH Asp D

Physical properties of amino acids

The simplest amino acid is glycine NH2CH2COOH

Its IUPAC name is 2 amino ethanoic acid

The physical properties of α amino acids are, a) They are generally

colourless crystalline solids.

b) They are highly polar and in aqueous solution they form zwitter ions.

c) In acidic solution, they form +ve ion and in basic solution they form

ve ion.

d) At a particular PH, the dipolar ion acts as neutral ion (iso electronic

point)

e) Except glycine, all other naturally occurring α amino acids are

optically active due to asymmetry at α Carbon.

f) Most of the naturally occurring amino acids are with L-Configuration

Physical Properties

At a particular pH, the dipolar ion of amino acid (zwitterion) acts as

neutral ion and does not migrate to cathode or anode in electric

field. This pH is known as iso electric point of the amino acid

The iso electric point depends on different groups present in the

molecule of the amino acid.

In neutral amino acids the pH range is 5.5 to 6.3 At iso-electric point,

amino acids have least solubility. So, it is used in the separation

of different amino acids obtained from the hydrolysis of proteins.

Except, glycine all other naturally occurring -amino acids are optically

active due to a symmetry at α carbon. So, α -amino acids exist in D

and L forms.

In Fischer projection, formulae carboxyl group is at the top and in the

D-form amino (−NH2) group is written on the right and in L form on the

left side.

Polypeptides

A dipeptide called

aspartame being 160 times sweeter to srcrose is used as substitute for

sugar.

Proteins

Their structures are studied at four different levels as,

1. Primary 2. Secondary

3. Tertiary and 4. Quarternary structures

PRIMARY STRUCTURES:

For a given polypeptide, amino acids are linked with each other in a

specific sequence. This is considered as primary structure of that

polypeptide.

Any change in this sequence produces a different protein.

Primary structure indicates the location of disulphide bridges if present.

SECONDARY STRUCTURE: It explains the shape of poly peptide chain

and describes the conformation of segments of the back bone chain

of a protein.To minimise the energy, a protein chain tends to fold in a

repeating geometric structure. This is based on

(i) the regional planarity about each peptide bond

(ii) maximising the number of peptide groups that engage in hydrogen

bonding.

(iii) sufficient separation between nearby R groups to avoid steric

hindrance and repulsion of like charges.

TERTIARY STRUCTURE: It indicates the three dimensional arrangement of

all the atoms in the protein.The tertiary structure is understood from

its primary structure and further folding of secondary structure in fibrous

and globular shapes.

The forces that stabilise secondary and tertiary structures are H-bonds,

disulphide linkages,vander Waals forces and electrostatic forces

of attraction.

QUARTERNARY STRUCTURE: Proteins that have more than one peptide

chain are known as oligomers. The individual chains are called subunits.

The subunits are held together by hydrogen bonding, electrostatic

attractions, hydrophobic interactions etc. Quarter- nary

structure explains the way the sub units are arranged inspace.

i.e. Proteins have four levels of structure:

i. Primary: Amino acid sequence.

ii. Secondary: Shape of back bone.Examples: α - helix, β - pleated

sheet.

iii. Tertiary: Folding of helix.

Examples:Folded helix in a globular protein.

iv. Quaternary: Interactions between two or more protein molecules.

EXAMPLES:The association of four globins inhemoglobin.

Peptides are formed by the condensation of two or more same or

different amino acids. They contain peptide linkage CO NH-.

Proteins are complex long polymers of amino acids linked by CO NH-

bonds.

The most energetically stable state of a protein is called its native state.

Denaturation of proteins

The process which changes the physical and biological properties of a

protein is called denaturation.

The denaturation is caused by changes in pH, temperature, presence

of some salts or certain chemical agents.

Denaturation is carried out by

a) Changing the pH

b) Adding reagents

c) Adding detergents

d) Heating

Denaturation can be carried out with out effecting the primary

structure of protein

Denaturation may be reversible or irreversible.

The coagulation of egg white on boiling is an irreversible denaturation.

Renaturation is the reverse of denaturation.

Enzymes

Enzymes are biological catalyst produced by living cells which catalyze

the biochemical reactions.

These are simple or conjugated proteins.

These are highly specific.

The non protein component of enzyme molecule is called a prosthetic

group.

The prosthetic group that is covalently bonded with the enzyme

component is called cofactor.

The prosthetic groups attached to the enzyme at the time of reaction

are called coenzymes.

Vitamins

Synopsis

Vitamins are naturally occurring low molecular weight carbon

compounds, which are essential dietary factors.

Their absence in the human body causes deficiency diseases or

disorders.

They participate in the production of co-enzymes and also in the

regulation of biochemical processes.

Classification of vitamins

Vitamins are classified into two broad groups.These are

(a) Fat soluble vitamins (b). Water soluble vitamins

FAT SOLUBLE VITAMINS:

Vitamins A,D,E and K are fat soluble. Liver cells are rich in fat soluble

evitamins (Vitamins A& D)

WATER SOLUBLE VITAMINS:

Vitamins C and B-complex are water soluble. These are present in

much smaller amounts in cells.

Important vitamins

Vitamin D2 is also called sunshine vitamin. Since it is obtained by

sunlight irradiation of ergosterol present in oils and fats

Vitamin B1 is a derivitive of pyrimidine as well as such it conforms both N

and S

Vitamin B12 contains both N and P

Pro vitamins are the biologically inactive compounds which can be

easily converted into biologically active vitamins

B-carotene is provitamin A

Nucleic acids

Synopsis

1. Nucleic acids are biologically significant polymers of nucleotides with

poly phosphate Ester chain.

2. These are present in all living cells.

3. They direct the synthesis of proteins and are responsible for the

transfer of genetic information i.e hereditary.

4. Nucleo-proteins are formed by combining proteins with nucleic acids

.Nucleo-proteins = protein + Nucleic acid

5. Proteins have polyamide chains.

6. The repeating units of nucleic acids are called nucleotides.

7. Types of Nucleotides ( Nucleic acid ) are

a) Ribonucleic acid ( RNA)

b) Deoxyribonucleic acid ( DNA )

Chemical composition

1. DNA+Hydrolysis→Deoxyribose+phosphoricacid+purine/pyrimidi

ne base

2. RNA+Hydrolysis→ribose+ phosphoric acid + purine / pyrimidine

base

3. Ribose (or) de-oxyribose is a pentose sugar

a) α−D− ribose present in RNA

b) α−D− deoxyribose present in DNa

4. Pyrimidines and purines are nitrogen containing hetrocyclic bases

5. Pyrimidinen bases are

a) Thymine (T) C5N2H6O2

b) Cytosine (C) C4N3H5O

c) Uracil (U) C4N2H4O2

6. Purine bases are

a) Adenine (A)C5N5H5

b) Guanine (G) C5N5H5O

7. a) Thymine contains two oxo and one methyl groups

b) cytosine contains one amino and one oxogroups

c) Uracil contains two oxogroups

d) Adinine contains one amino group

e) Guanine contains one amino and oneoxogroups.

Chemical composition

DNA contains A, G,T and C

RNA contains A , G, U and C

Thymine is not present in RNA.

Nucleoside

1. N- Glycosides are called Nucleosides.

2. Nucleoside = Nucleic acid bases + pentose sugars

3. The bond present between sugar and base is called N-Glycoside

bond.

4. This bond is formed between first numbered nitrogen of pyrimidine

and first carbon of sugar.

5. This bond is formed between ninth numbered nitrogen of purine and

first carbon of sugar.

6. These are called as adenosine . guanosine ,cytidine , thymidine and

uridine, when they contain adenine, guanine, cystosine, thymine and

uracil respectively.

Nucleottide

Nucleotide = Base + Sugar + phosphate

1. Base is nothing but purine ( or ) pyrimidine

2. Base bonded with sugar at 1I carbon.

3. Phosphate group bonded with sugar at 3I or 5I carbons.

4. 1 to 3 phosphate groups may attach with sugar.

Nucleic acids

1. Nucleic acids = Nucleotide sub-units linked by phosphate diester

bonds.

2. AMP , ADP , ATP , d AMP , d ADP etc are called Nucleotide sub-units.

3. These nucleotides connected by mono , di (or) tri phosphate groups

at 5I OH of one nucleotide.

4. A Nucleic acid contains one nucleotide and 3I OH of another

nucleotide.

a) Phosphate diester bonds which links two sugar rings.

b) α - Glycoside bond which links Sugar and base.

5. a) A nucleotide contains two nucleotide sub-units called

dinucleotide.

b) A nucleotide contains 3 10 subunits is called Oligonucleotide

c) A nucleotide containing many subunits is called Polynucleotide

6. DNA and RNA are Polynucleotides.

7. A nucleic acid chain is abbreviated by one letter code with 5 end of

the chain.

8. The abbreviated ACG trinucleotide shown as A C G.

DNA-Double helix

1. It explains base

equivalence and duplication of DNA.

2. All species contains

a) A = T b) C=G

c) no. of purines = no. of pyrimidines (A+G)=(C+T) 3. The AT / GC ratio varies from species to species Ex . a) In human

being AT/GC=1.52/1

b) In E. coli AT/GC=0.93/1

4.It is composed of two right handed helical polynucleotide strands.

5. The two strands are anti parallel with each other.

6. 5 3 phospho diester linkages run in opposite direction.

7. The base groups are present inside and perpendicular with the axis.

8. The two stands are held together by hydrogen bonds due

to A=Tand G=C

9. Always A pairs with T and G pairs with C only.

10. A forms two hydrogen bonds with T.

G forms three hydrogen bonds with C

A does not form Hydrogen bonds with C

G forms only one hydrogen bond with T.

11. The length of all hydrogen bonds are similar

12. DNA strands are twisted but base pairs are planar and parallel with

each other.

13. Primary structure of nucleic acids explains order of bases.

14. Secondary structure gives double helix.

15. The stability of helix is due to

16. Hydrogen bond between A=T and G=C

17. Hydrophobic interactions between bases.

18. The diameter of double helix is 2 nm.

19. The length of one complete turn (3600) is 3.4nm.

20. The DNA rotates at both sides i.e right hand side or left hand side.

21. The right hand helices is more stable and is called α conformation.

22. At melting temperature, DNA separates into two strands, called as

melting.

23. When the melted DNA is cooled, the strands hybridise. This is called

Annealing.

24. In the secondary structure of RNA , helices are present but only

single stranded.

Protein synthesis Translation

1. The process by which the genetic message in DNA that has been

passed to mRNA is decoded and used to build proteins is called

translation.

2. During the transcription, the DNA language changes to language of

Amino acids.

3. The sequence of three bases is called codon.

4. The amino acid, specified by each three bases sequence, is called

the genetic code.

5. Total of 64 codons and 20 amino acids are present.

6. One amino acid may have more than one codon. Ex : CUU and

CUC both code for leucine.

7. A difference of simple base in the DNA molecule causes a change in

the amino acid sequence which leads to mutation.

8. Every t RNA molecule has an amino acid attachment site.

9. The genetic code has four important features.

a. it is universal b. it is commaless

c.it is degenerate

d.The third base in the codon is not always specific.

Lipids

Synopsis

Lipids are naturally occurring carbon compounds related to fatty acids

and include esters of fatty acids or substances capable of forming

such esters.

Lipids are insoluble in water but soluble in organic solvents like

chloroform, ether, benzene etc.

The common lipids are oils, fats, waxes, steroids, terpenes, phospolipids

& glycolipids.

These are all stored in adipose tissues and are present in all organisms

including viruses.

Classification of lipids

Lipids are classified into three types:

i. Simple lipids (homolipids)

ii. Compound lipids (hetero lipids)

iii. Derived lipids (compounds obtained from simple and compound

lipids)

Simple lipids are alcohol esters of fatty acids and include neutral fats

and waxes.

These are long chain, fatty acid esters of trihydric alcohol glycerol.

These fatty acids contain even number of carbon atoms and are both

saturated and unsaturated carboxylic acids

Simple lipids are known as triglycerids (or) triacyl glycerols. Some of

these are solids while other are liquids at room temperature. Solids are

known as fats and liquids are known as oils.

Hormones

Synopsis

Hormones are molecules of carbon compounds, that transfer

biological information from one group of cells to distant tissues or

organs.

Hormones are of animal (Human) origin and plant origin.

Animal (or human) hormones are produced by specialized tissues in the

body in small amounts. These tissues are called the endocrine

or ductless glands.

Hormones are liberated directly into the blood stream and are carried

from there to the remote tissues or vicera, called target organs.

The hormones exert characteristic physiological effects on the target

organs and also control metabolic activities.

Plant hormones are called growth hormones.

Hormones name indicates the stimulating action (in greek hormosin

means to excite).

Hormones are all generally proteins but not all of them are proteins.

In many cases, hormones act by influencing the enzymes.

Classification of hormones

Hormones are classified into three groups on bases of their chemical

structures.

1. Steroid hormones : These are produced by the adrenal cortex, testis

and ovary.

2. Protein hormones : These are produced by pancreas, parathyroid,

pituitary and the gastro internal mucosa.

3. Amino acid derivatives : These are produced by thyroid and adrenal

medulla.

Structure

Steroid hormones are

compounds, whose structure is based on four ring network.

Three of these rings are 6-carbon rings and one is 5-carbon ring.

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