BIOLOGY AS LEVELREVISION 01

1. BIOLOGICAL MOLECULESAnd the Components of Life

Definitions

Organic Molecules: Any Compound containing Carbon and Hydrogen

Macromolecule: A large biological moleculeMonomer: A relatively simple molecules used

as a building for polymerPolymer: A giant molecule made up of many

subunits of polymer joined togetherPolarity: The uneven distribution of charge

Introduction

4 Biological Molecules: Hydrogen, Carbon, Oxygen

Carbon – is able to join with up to 4 atoms – very versatile and stable – form chains/ ring structures

Monomer: A simple molecule – basic building block e.g. Monosaccharide, Nucleotides, amino acids

Polymer: Many repeating subunits of monomers joined together e.g. Polysaccharides, Nucleic Acid, Proteins

Ionic vs. Covalent bond

Ion: Molecules that are charged

Ionic do not share electron

One donates electron to fulfill the other’s octate

One becomes – The other becomes + Hence, they become

charges

When they share electrons

When one molecule shares certain electrons with the other – both using them – to create a bond

Equally distributed – non-polar

Slightly charges - polar

The Hydrogen Bond

The small charge between the H minus and Oxygen plus between different water molecules

This can work with any of the 3: F, O, N

About Carbon

Doesn’t take up a lot of spaceCan combine with a lot of other moleculesNeed 4 extra electronsAlso not too reactive

The Properties of Water

Hydrogen bonding qualitySolvent property – Derived from hydrogen

bondThermal Properties – High specific heating

capacity/ High heat of vaporization

Solvent Property

Positively charged part of ions are attracted to the negatively charged part of the water molecules – causing hydrophilic substance to dissociate

The substance becomes hydrated

Dissolve: Glucose, amino acid, hemoglobin, enzymes, hormones, vitamins, respiratory gases

CARBOHYDRATE

Carbohydrates

Carbon, Hydrogen, OxygenUsed as a source of energy in the form

of glucoseStored in the form of starch/ GlycogenStructure in the form of cellulose (CH2O)n

MonosaccharideSimple Sugar – Triose,

Pentose, HexosePentose (Ribose, Deoxyribose)Hexose (Glucose, Fructose,

Galactose)Pentose and Hexose have

long carbon chains that can form a stable ring structure

2 forms of chemicals – isomers (Alpha and Beta)

Alpha and Beta

Carbon atom number 1 – has hydroxyl groupHydroxyl group could be above or below the

ring If above the ring: Beta glucose If below the ring: Alpha glucose

Monosaccharides for energy

The Carbon-hydrogen bond is largeCan be broken down to make energyAssist the making of ATP

Disaccharide

Joined by 1,4 glycosidic bond – condensation reaction (loses H2O)

Split by the adding of water – hydrolysis (gains H2O)

Maltose = Alpha Glucose + Alpha GlucoseSucrose = Alpha Glucose + FructoseLactose = Beta Galactose + Alpha Glucose

Polysaccharides

Polymer: Many repeating subunits of monomer joined together to form a large molecule

Many monosaccharide form polysaccharide Starch, Glycogen, CelluloseThese are not sugars

Starch

Mixture of Amylopectin and AmyloseAmylose: Many alpha-glucose linked by 1.4 –

helical structure (makes it compact)Amylopectin: Amylose with shorter chains of

alpha glucose with 1,6 glycosidic branches

Glycogen

Amylose + Amylopectin – with more 1,6 chains

Shorter amylose chainsAllow it to be less compact – quicker releases

of energy in animal bodies

Cellulose

A polymer of beta-glucoseTo connect by 1,4 glycosidic bond, one

glucose of a pair has to flip 180 degreesThis arrangement creates weak hydrogen

atom with an oxygen molecule in the same cellulose

The most abundant molecules in nature (in cell wall, also hard to break down)

Cellulose

50 – 60 cellulose molecules are cross-linked side by side by hydrogen bond to form microfibrils

Microfibrils bundled up to form a fiber

LIPID

Lipids

Contain: Carbon, Hydrogen, OxygenExcept for glycerol – insoluble in waterDissolve in Chloroform/ BenzeneLess dense than water

Lipids

TriglyceridePhospholipidsCholesterol

Triglyceride

Glycerol (Three-carbon Alcohol)Fatty Acid (Acid)- A carboxyl group with carbonskeleton

Triglyceride

Combination of glycerol(alcohol) and 3 fatty acid molecules

Glycerol: A three carbon alcoholEster bond is formed in the condensation

between an alcohol group and an acid groupCan have tails that are 14 – 22 carbon atoms

longLong tails – insoluble in water

Saturated/ UnsaturatedFatty acid chains with

double bonds – are not saturated with hydrogen- they are bent in the middle – is called UNSATURATED (better for your body – liquid at room temperature hence accumulate less)

Fatty acid chains with no double bond – are saturated with hydrogen – is called SATURATED

Functions of Lipids Energy Source (soluble/mobile respiratory substrate) –

Glycerol + Fatty Acid Insoluble energy store – Fats/ Oils Thermal insulation – fats Buoyancy – fats Protection for vital organs – fats Waterproofs – waxes for plants (Suberin, cutin) Solvent for certain vitamins (A,D,E,K) Cell membranes (Phospholipids, glycolipids, cholesterol)

Biological functions of Triglycerides

Fat yields more energy than carbohydrates

They also yield water in metabolic reaction – desert animals

Fats of whales in Arctic and Antarctic regions

Blubber of seals/ walrus – help them float

Mammalian kidney has fat

PROTEIN

Proteins C, H, O, N 20 different types Bond: Peptide bond (Formed by condensation)

(broken by hydrolysis) One’s Carboxyl loses a hydroxyl group, the other’s Amine

loses a hydrogen atom A single protein can have 1 polypeptide chains or many

combined Synthesized in ribosomes, broken down (hydrolyzed) in

the stomach by protease

Amino Acid

Organic molecules with carboxyl and amino groups

They differ in properties according to its R-group

E.g. Glycine – has hydrogen R-group

The Primary Structure

A chain/ sequence of amino acid linked by peptide bond forming a polypeptide

A change in one amino acid can make a different protein

The Secondary Structure

The structure of protein caused by the regular coiling or folding of a polypeptide or protein.

The chain coils up in a corkscrew shape – due to the hydrogen bond between the oxygen of the carboxyl group with the hydrogen of the amine group 4 places ahead of it. – a-helix

ProblemsElectrostatic chargesProlineTemperature

The Secondary Structure

Beta Pleated SheetPolypeptide chains – adjacent Parallel or anti-parallel – R groups alternate pointing up/ down

Held together via hydrogen bond

The Tertiary Structure

Fibrous:

Do not fold upon itself, long rod, strong structure, typically insoluble, (collagen, keratin)

Globular:

Polypeptide backbone folds upon itself, compact and spherical, typically water soluble (Hemoglobin, Enzymes)

Globular ProteinH2O

H2O

H2O

H2O

HYDROPHILICHYDROPHILICHY

DROP

HILIC

HYDROPHILIC

Globular ProteinH2O

H2O

H2O

H2O

Hydrophobic effect

Globular ProteinH2O

H2O

H2O

H2O

Hydrogen bond between R groups side chains

Disulfide bond – between Sulfur

Ionic bondBetween ionized carboxyl,Amine groups

Fibrous Protein

1. Sequence of polypeptide form an helical shape – not tightly wounded.

2. 3 of these chains are tied around each other by hydrogen bond and some covalent bond

3. Glycine is at every 3rd amino acid – the small size allow for tight wounding

4. They lie side by side – cross links are created – out of step to increase strength – strong bundle: fibril

5. Many fibrils = fibers

Uses of Proteins

Transport – Hemoglobin, Myoglobin – transport protein in cells

Storage – OvalbuminEnzymesHormones Immune system – AntibodiesParts of the phospholipid membraneStructure – fibrous protein, collagen, keratinMuscle – Actin, Myosin