Biological Molecules: - Carbohydrates

- Carbohydrates - 

- Monosaccharides - 

The monomer for carbohydrates is called monosaccharides. 

Common forms of monosaccharides are 

- Glucose 

- Galactose 

- Fructose 

In order for a two monosaccharides to form, there needs to a condensation reaction.

The bond that is formed between = glycosidic bond.

2 monosaccharides with a glycosidic bond in between = Disaccharide

- Disaccharides -

Examples of this = 

The picture above shows the different types of disaccharides and the structures for each of them. 

Glucose is needed for each of the disaccharide formation. 

This is because Glucose is an isomer

Glucose has 2 isomers - 

- (Alpha) α-glucose 

- (Beta) β-glucose 

As shown above which has been circled, the positioning of the OH is the difference in the structure of both molecules. This can make all the difference in a molecule, which can change its function, structure, etc. 

- Polysaccharides -

A polysaccharide is formed from many glucose units by condensation. 

There are 3 forms of polysaccharides that are needed to be known: 

- Glycogen } formed by the condensation of α- glucose.

- Starch } formed by the condensation of α- glucose.

- Cellulose } formed by the condensation of β- glucose. 

Glycogen vs Starch 

Starch: 

Main role = energy store 

Structure is suited for the molecule, reasons being it's:

✔ Insoluble ⇒ does not effect water potential (water not drawn by osmosis).

✔ large & insoluble ⇒ does not leave the cell.

✔ compact ⇒ can be stored in small places.

✔ hydrolysed = α- glucose, can be transported & readily used in respiration.

✔ branched form = enzymes, simultaneously, can act on the polymer releasing α- glucose.

Glycogen: 

Main role = major carbohydrate store in animals

✔ Insoluble = does not effect water potential (osmosis) // does not diffuse out of the cell.  

✔ Compact = huge amounts can be stored in a small space. 

✔ Highly branched = ends are acted on simultaneously by enzymes, rapidly broken to form glucose monomers - respiration. 

Cellulose

Unlike Starch and Glycogen, cellulose is not formed from α- glucose. 

β- glucose is building blocks of cellulose. The small variation produces a fundamental difference in the structure and the function of the polysaccharide. 

Cellulose:

Main role = providing support and rigidity

✔ forms long single un-branched chains.

✔ run parallel to each other // crossed linked by hydrogen bonds add collective strength. 

✔ grouped to form micro-fibrils which are grouped forming fibres // adds more strength.