Biological molecules

Ruby Zhao

2009. 9.1

Biological molecules

• Molecular Biology- study of the structure and functioning of biological molecules.

Introduction

• The building blocks of life• Polymers 聚合物 macromolecules 高分子

• Carbohydrates 糖类• Lipids 脂类• Proteins 蛋白质• Water 水• Inorganic ions 无机离子

Metabolism

• The sum total of all the biochemical reactions in the body is known as metabolism.

The building blocks of life

• The four most common elements in living organisms are Hydrogen Carbon & Oxygen and Nitrogen.

Polymers and macromolecules

• The term macromolecule means ’giant

molecule’.

• Polymers is macromolecules made up

of many repeating subunits that are

similar or identical to each other and

are joined end to end like beads on a

string.

• Polymerisation- the same reaction

repeated many times for subunits to

form polymers.

The building blocks of life

monosaccharides

polysaccharides

Organicbases

aminoacids

Fatty acids and glycerol

proteins lipids

nucleotides

Nucleic acids

Carbohydrates

• All carbohydrate contain the elements

Carbon Hydrogen & Oxygen. The general

formula for a carbohydrate is Cx(H2O)y.

• There are 3 types:

Monosaccharides

Disaccharides

Polysaccharides

Monosaccharides

Consist of a single sugar molecule (CH2O)n

• If n=3, triose (glyceraldehyde)• If n=5, pentose (fructose,

ribose)• If n=6, hexose (glucose,

galactose)

Molecular and structural formulae

Glucose• Molecular formula C6H12O6.

• Structural formula

fructose

ribose

Isomerism

• They can exist as isomers: & glucose

Roles of monosaccharides

• Monosaccharides are used for– Energy– Building blocks

Disaccharides

• Formed from two monosaccharides• Joined by a glycosidic bond

• A condensation reaction:– glucose + glucose maltose– glucose + galactose lactose– glucose + fructose sucrose

• Condensation reaction 缩合反应 : two hydroxyl groups line up together and one combines with a hydrogen atom from the other to form a water molecule.

• The reverse of this kind of condensation is the addition of water which is known as hydrolysis reaction水解反应 .

Polysaccharides

• Polymers formed from many monosaccharides

• Three important examples:– Starch– Glycogen– Cellulose

Starch

• Amylose

-glucose1,4 glycosidic

bondsSpiral structure

• Amylopectin

-glucose1,4 and some 1,6

glycosidic bondsBranched

structure

Starch

Insoluble store of glucose in plantsformed from two glucose polymers:

Glycogen

• Insoluble compact store of glucose in animals

-glucose units• 1,4 and 1,6

glycosidic bonds• Branched

structure

Cellulose

• Structural polysaccharide in plants

-glucose• 1,4 glycosidic bonds• H-bonds link adjacent

chains

summary

Type subunits

glycosidic bonds

function

Amylose -glucose

1,4 Energy source

unbranched

Amylopectin

-glucose

1,4 & 1,6

Energy source

Branched

Gylcogen -glucose

1,4 & 1,6

Energy source

Branched

Cellulose -glucose

1,4 support unbranched

Hydrophilic

• Molecules which have groups with dipoles are said to be polar. They are attracted to water molecules, because the water molecules also have dipoles.

• Such molecules are hydrophilic (water-loving), and they tend to be soluble in water.

Hydrophobic

• Molecules which do not have dipoles are said to be non-polar. They are not attracted to water, and they are hydrophobic (water-hating).

Lipids

• Made up of C, H and O• Can exist as fats, oils• They are insoluble in water• They are a good source of

energy (38kJ/g)• They are poor conductors of heat• Most fats & oils are triglycerides

ester

• Alcohols are molecules containing the –OH functional group.

• Carboxylic acids make up a homologous series of compounds containing the functional group –COOH.

• Esters are made of reaction of alcohols and carboxylic acids.

Triglycerides

• Formed by esterification…• …a condensation reaction

between 3 fatty acids and glycerol:

Glycerol

H

C

H C

C

H

H

H

H

O

O

O

Fatty acids• Carboxyl group (-COOH) • attached to a long non-polar

hydrocarbon chain (hydrophobic):

H

H

C

HH

C

H

H

C

HC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

A saturated fatty acid (no double bonds)

HH

C

O

O

H

C

HH

C C

C C H

C

H

H

C

H

HA polyunsaturated fatty acid

C

O

O

H

C

HH

C

H

H

C

H

H

C

H

C

HH

C

H

H

C

H

H

A monounsaturated fatty acid

H H

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

Glycerol Fatty acid

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

Glycerol Fatty acid

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

HGlycerol Fatty acid

Esterification

H

C

H C

C

H

H

H

H

O

O

OC

O

O

H

C

HH

C

H

H

C

H

H

C

H

H

Ester bond

water

Esterification

• This happens three times to form a triglyceride:

glycerol fatty acids

Phospholipids

• One fatty acid can be replaced by a polar phosphate group:

glycerol Hydrophobic fatty acids

hydrophilicphosphate

Functions of lipids

1. Protection of vital organs2. To prevent evaporation in plants

& animals3. To insulate the body4. They form the myelin sheath (髓

鞘 ) around some neurones5. As a water source (respiration of

lipids)6. As a component of cell

membranes

Proteins• Made from C H O N & sometimes S• Long chains of amino acids• Properties determined by the aa

sequence

Amino acids

H

CH

N C

HH

O

O

R

~20 aaGlycine R=HAlanine R=CH3

aminecarboxyl

Peptide bonding

HC

HN C

HH

O

O

R

HC

HN C

HH

O

O

R

Peptide bonding

HC

HN C

HH

O

O

R

HC

HN C

HH

O

O

R

Peptide bonding

H

CH

N C

HH

O

O

R

HC

HN C

HH

O

O

R

Peptide bonding

CH

N C

HH

OR

HC

HN C

H

HO

H

O

O

R

water

Peptide bond

A condensation reaction

Peptide bonding

CH

N C

HH

OR

HC

HN C

H

O

O

R

A dipeptide

Primary structure

• The sequence of aa is known as the primary structure

• The aa chain is a polypeptide

• Peptide bond forms between the –COOH and the -NH2 of

adjacent aa

• This results in the chains folding:

Secondary structure

-helix -pleated sheet

Secondary structure

• A polypeptide chain often coils into an α-helix due to the attraction between the oxygen of the –CO group of one amino acid and the hydrogen of the –NH group of the amino acid four place ahead of it.

Secondary structure

-pleated sheet is a looser straight shape .

Tertiary structure

• A protein coils up to form a precise three-dimensional shape is its tertiary structure.

Tertiary structure

• Bonding between R-groups gives rise to a 3D shape

• H-bonds =O - HN-

• Ionic bonds –NH3-COO-

• Disulphide bridge (most stable)

--CH2S-SCH2-

affected by temp & pH

affected by pH

affected by reducing agents

Quaternary structure

• The association of different polypeptide chains is called the quaternary structure of the protein.

Quaternary structure

• Some proteins have more than one polypeptide chain

• Each chain is held together in a precise structure

• eg Haemoglobin

Types of proteins

• Fibrous proteins– e.g. collagen– Insoluble– structural

• Globular proteins– e.g.enzymes– Soluble – 3D shape

Haemoglobin

A complete haemoglobin can carry Four O2

collagen

Functions of proteins

• Enzymes – • Transport – • Movement – • Cell recognition –• Channels –• Structure –• Hormones – • Protection –

AmylaseHaemoglobinActin & myosinAntigensMembrane

proteinsCollagen & keratinInsulinAntibodies

Water

• Water is a polar molecule• It forms weak hydrogen bonds • It remains a liquid over a wide

temperature range• Water molecules stick to one

another = cohesion (surface tension)

• Water molecules stick to other substances = adhesion (capillarity)

O

H

H

+

+-

Water• It has a high specific heat capacity – so

water can maintain a reasonably

constant temperature (homeostasis)

• It has a high latent heat of vaporisation

– so animals use water to cool

themselves

• It is less dense as a solid (ice)…

• … and ice is a poor conductor

• Water is a good solvent

Inorganic ions

• Ions are formed individual atoms that have gained or lost one or more electrons and are therefore charged negatively or positively.

• Many ions are highly soluble in water.

The end