Biology- Polysaccharides

What is a polysaccharide?

A polysaccharide is formed when more than two monosaccharides are joined together by condensation reactions. Polysaccharides are carbohydrates. Police that cried molecules are made from large numbers of their monomers (Monosaccharides).

Example:

How can polysaccharide be broken down?

Polysaccharides can be broken down into the constitution monosaccharides by hydrolysis reactions

Example

Functions of polysaccharides

Starch

Cells get energy from glucose. Plants store excess glucose as starch ( when a plant needs more glucose for energy, it breaks down the starch to release the glucose). Starch is a mixture of two polysaccharides of alpha glucose , amylose and amylopectin

Amylose

Amylose is a long unbranched chain of a-glucose. The angles of the glycolic bonds give it a coiled structure almost like a cylinder. This makes it compact so it’s really good for storage because you can fit more into a small space

Amylopectin

Amylopectin Is a long branched chain of a-glucose. It’s side branches allowed the enzymes that breakdown the molecule to get at the glycolytic bonds easily. This means that the glucose can be released quickly

Starch is insoluble in water and doesn’t affect water potential so it doesn’t cause water to enter cells by osmosis which would often make them swell. This is good for storage

Glycogen

Animal cells get energy from glucose too. But animal start excess glucose is glycogen another polysaccharide of alpha glucose. It structure is very similar to amylopectin, Except that it has loads more side branches coming off it. Loads of branches means that starred glucose can be released quickly, which is important for energy release in animals.

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

Cellulose

Cellos is made of long unbranched chains of beta glucose. When beta glucose molecules bond, they formed straight cellulose chains. The cellular chains are linked together by hydrogen bonds to form strong fibre is called microfibrils. The strong fibres means cellular provides structural support for cells (e.g in plant cell walls).

Iodine test for starch

If you wanted to test for the presence of starch in a sample, you’ll need to do the iodine test. Just add iodine dissolved in potassium iodide solution to the test sample. If there is starch present the sample changes from brownie orange to a dark blue black colour