1.2 Carbohydrates

Biochemistry: Carbohydrates Proteins

Why study biochemistry?

Some examples:

• To understand how reactions in cells work • To make drugs that can interfere with

chemical reactions that we don’t want – e.g. create drugs that stop growth of cancer cells • Produce vaccines for disease we cannot

otherwise treat

but….

• There are many strange looking molecular structures and unfamiliar names.

• You cant see molecules with a microscope – not even an electron microscope. However, there is a method of

seeing what they look like using x-ray crystallography.

The Reward…

• For those who persevere with Biochemistry at

degree/ masters/ PhD level, biochemistry is BIG business.

• Pharmaceutical

companies make big money and also by

Life is made up of 4 main types of

molecule

• Carbohydrates • Lipids

• Proteins

• Nucleic acids (e.g. DNA and RNA)

• _{Name anything that’s living and it will be made up of}

molecules from the list above (plus water).

Monomer

– single identical repeating

units that……

……are joined together to form

Join together to

form a

polymer

Lots of

monomers

Polysaccharides

Proteins

Lipids

Glucose

Amino acids

Glycerol & fatty

acids

MONOSACCHARIDES

• A single sugar unit • Sweet and soluble

• Contain carbon, hydrogen & oxygen

Classified according to the number of carbons a molecule has:

Monosaccharides

substances

• General formula (CH2O)n

• N can be any number from 3 to 7 • The 3 most common are:

Formula Name E.g.

N=3 Triose Glyceraldehydes

N=5 Pentose Ribose, Deoxyribose N=6 Hexose Glucose, Fructose,

Pentose and hexose sugars exist in two forms. Here are three hexose sugars in their ring form:

Straight chain forms

C

H

O

C

H

O

C

H

O

Hydrogen

Carbon

GLUCOSE comes in 2 forms, this one;

Here this H is above

the carbon.

Here this H is below

the carbon.

This is called β (beta) glucose.

Both these molecules are glucose.

Both have a molecular formula of C₆H₁₂O_6. But they are structurally different.

Function of Monosaccharides

• As an energy source - a large amount of energy is stored between the C-H bond which is released to form ATP. ATP is the energy currency of the cell.

• Two sugar molecules joined together

Type of

disaccharide

Monosaccharides it’s made up from

Sucrose Fructose + Glucose

Maltose Glucose +

α-Glucose

Lactose Glucose +

Forming a disaccharide - MALTOSE

• Two α glucose molecules C1 & C4 meet. OH (hydroxyl group) & H react.

• This causes water to be formed – it is therefore known as a - condensation reaction.

Polysaccharides

STARCH CELLULOSE GLYCOGEN CHITIN

• Polymers with subunits of monosaccharides • Repeated condensation reactions

Polysaccharide Monosaccharide it’s made from

Starch α-glucose

Glycogen α-glucose

Cellulose β-glucose

Chitin N-acetylglucosamine

Starch

Made up of two types of substances:

1)Amylose 2) Amylopectin

1.Amylose

• Condensation reactions between α-glucose (many α-1,4 glycosidic links).

Spiral structure of

2. Amylopectin

• Condensation reactions between α glucose molecules (α-1,4 glycosidic links).

• Branches of α-1,6 links also exist.

Properties of Starch

• Amylose and amylopectin are compact – they can be stored in a very small amount of space • Easily broken down by enzymes to release

sugar residues (molecules) for respiration • Insoluble. Starch does not affect the water

1-4 links form a helical structure

Amylopectin

Starch grains are a mixture of amylose & amylopectin

Starch is a polysaccharide

Starch it is a insoluble store of glucose

Glycogen

• Main storage polysaccharide in animals and fungi

• Similar to amylopectin but with many more branches

(caused by -1,6 glycosidic bonds between glucose molecules) which are also shorter.

GLYCOGEN is the storage

polysaccharide in animals

Cellulose

• Present in plant cell walls.

• It is the most abundant organic molecule on the planet!

• It is mechanically very strong.

Cellulose

• C 1-4 links make up this polysaccharide.

• If C1 and C4 are to react, one β-glucose

molecule needs to flip through 180o_{. It is this}

• This structure has H-bonds holding it together • Cellulose molecules lie side by side with one

another and are held together by hydrogen bonds (H bonds) to form microfibrils.

• Several microfibrils bind together with H bonds to form fibres

(a) Cellulose fibre

(b) Fibre

(c) Microfibril

(d) Chains of cellulose molecules

70 chains of β glucose combine to form a

MICROFIBRIL.

Lots of MICROFIBRILS are held together to form

Chitin

• Chitin is the main component of fungal walls and the exoskeletons of insects and crustaceans

• It is composed of N-acetylglucosamine which

contain Nitrogen. This is very similar to B-glucose with one hydroxyl group on each monomer

substituted with an acetyl amine group. The units are joined by 1,4 bonds β

• This allows for greater H-bonding between the polymers giving the chitin matrix increased

MARK SCHEME Qu. 2 p70

• Glycogen – a, 1,4 glycosidic bonds With a 1, 6 sidebranches

Shorter and more frequent than amylopectin V Quickly broken down

Starch – Amylose – a1,4 glycosidic bonds Spiral – compact

Amylopectin – a1,6 branches

So can be more frequently broken down Both used for storage