Biology Unit 2: Variation in Carbohydrates

Carbohydrates are made from monosaccharides.

Glucose comes in two forms, alpha and beta glucose, you need to know the structure of both!

You should already know the structure of alpha-glucose.. beta-glucose is basically the same, but the OH and H on the right are swapped around.

When monosaccharides join, a molecule of water is released.

This is called a condensation reaction.

The bonds that join sugars together are called glycosidic bonds.

Cellulose is formed when beta-glucose is linked by condensation.

Starch is the main energy storage material in plants.

Cells get energy from glucose. Plants store excess glucose as starch.

Starch is a mixture of two polysaccharides of alpha-glucose - amylose and amylopectin.

Amylose - a long, unbranched chain of alpha-glucose. The angles of the glycosidic bonds give it a coiled structure. This makes it compact, so it's really good for storage.

Amylopectin - a long, branched chain of alpha-glucose. It's side branches allow the enzymes to break down the molecule to get at the glycosidic bonds easily.

Starch is insoluble in water so it doesn't cause water to enter cells by osmosis.

It's the main energy storage material in animals.

Animal cells get energy from glucose too. But animals store excess glucose as glycogen - another polysaccharide of alpha-glucose.

It's structure is very similar to amylopectin, except that it has loads more side branches. Loads of branches means that stored glucose can be released quickly.

It's also a very compact molecule, so it's good for storage.

The major component of cell walls in plants.

Cellulose is made of long, unbranched chains of beta-glucose.

The bonds between the sugars are straight, so the cellulose chains are straight.

The cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres mean cellulose provides structural support for cells.