Biological Molecules - Polysaccharides Flashcards
What are polysaccharides
They are carbohydrates
How are polysaccharides formed
Formed when more than 2 monosaccharides are joined together by a condensation reaction
How can polysaccharides be broken down
Can be broken down into their constituent monosaccharides by hydrolysis reactions
Give some examples of polysaccharides
Starch, glycogen and cellulose
What two polysaccharides is starch made from
Both alpha glucose:
- amylose
- amylopectin
Describe the structure of amylose
Long, unbranched chain of a-glucose, the angles of the glycosidic bond give it a coiled structure, which makes it compact which means its really good for storage because you can fit more in to a small space.
Describe the structure of amylopectin
Long, branched chain a-glucose. It has side branches that allow the enzymes that break down the molecule to get at the glycosidic bonds easily. This means that the glucose can be released quickly
How is starch good for storage
It is insoluble in water and it doesn’t affect water potential so it doesn’t cause water to enter cells by osmosis, which would make them swell
How do plants store excess glucose
Plants store excess glucose as starch, when a plant needs more glucose for energy, it breaks down starch to release the glucose
How do animals store excess glucose
Animals store excess glucose as glycogen which is another polysaccharide of a-glucose
Describe the structure of glycogen
Its structure is very similar to amylopectin, except that it has lots more side branches coming off it. Lots of branches means that stored glucose can be released quickly which is important for energy release in animals. Its also a very compact molecule so its good for storage
Describe the structure of cellulose
Long, unbranched chains of B-glucose. When the beta glucose bond they form straight cellulose chains. 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
What test do you use to test for starch
Iodine Test
Describe how to test for starch using the iodine test
Add iodine dissolved in potassium iodide solution to the test sample.
What are the results if starch is present
If there is starch present, the sample changes from browny orange to a dark blue-black colour
