Biological Molecules

Polymers

Most carbohydrates, proteins and nucleic acids are polymers.

Polymer: A large, complex molecule made up of long chains of molecules joined together.

Monomer: A small, basic molecular unit, e.g. monosaccharides, amino acids and nucleotides. 

Condensation reaction: When two molecules are joined together with the formation of a new chemical bond. A water molecule is released when the bond is formed.

Hydrolysis reaction: Breaks the chemical bond between monomers using a water molecule.

Carbohydrates

Carbohydrates are made from monosaccharides such as glucose, fructose and galactose. There are two types of glucose, alpha and beta glucose. (Alpha = H above, Beta= H below)

Monosaccharides are joined together by condensation reactions to form disaccharides. A glycosidic bond forms between two monosaccharides as a molecule of water is released.

Monosaccharide

Monosaccharide

Disaccharide

Glucose

Glucose

Maltose

Glucose

Fructose

Sucrose

Glucose

Galactose

Lactose

All sugars can be classed as reducing sugars or non-reducing sugars. Reducing sugars include all monosaccharides and some disaccharides, like maltose and lactose. Sucrose is a non-reducing sugar.

 To test for reducing sugar:

·        You add benedict’s reagent (blue) to the sample

·        Heat it in a water bath

·        A positive result would show a colour change from blue to brick red.

To test for non-reducing sugar:

·        Add dilute hydrochloric acid and heat in a water bath to break down the sugar.

·        Neutralise the solution by adding sodium hydrogencarbonate.

·        Carry out benedict’s test for reducing sugar.

Polysaccharides are formed when more than two monosaccharides are joined together by condensation reactions.

Starch

Glycogen

Cellulose

Found in plants. Mainly in seeds and storage organs.

Found in animals and bacteria. Mainly in the muscles and the liver.

Found in plant cells. It is a major component of plant cell walls.

Made up of unbranched (amylose) or branched (amylopectin) chains of alpha glucose.

Made up of alpha glucose in a similar structure to amylopectin, except with a lot more branches that are shorter.

Has straight, unbranched chains of beta glucose. Chains are linked by hydrogen bonds

Mainly used for energy storage

Main store of carbohydrates in animals. Releases energy.

Structural strength in plant cell walls.

It is insoluble so does not affect water potential so water is not drawn into the cell by osmosis.

It is insoluble so does not affect water potential so water is not drawn into the cell by osmosis.

Exerts an inward pressure to prevent any further influx of water thus stopping the cell from bursting and keeping it turgid.

Large and insoluble so does not diffuse out of the cell.

Being insoluble, it does not diffuse out of cells.

Not broken down by enzymes.

Amylose (1-4) forms a coiled chain which makes the molecule more compact, so a lot can be stored in small spaces.

It is compact so can be stored in small spaces.

Chains of cellulose run parallel to each other allowing hydrogen bonds to form cross linkages between adjacent chains. Many hydrogen bonds…