A - 3 - Polysaccharides Flashcards
What is a polysaccharide?
Carbohydrates that are formed when more than two monosaccharides are joined together by condensation reactions
Name the two polysaccharides starch is made from
Amylose
Amylopectin
What is the function of starch?
Plants store excess glucose as starch
It is an energy storage molecule
Describe the structure of Amylose
- A long unbranched chain of a-glucose
- It has a coiled structure which makes it compact
How does the structure of Amylose relate to its function?
Its coiled structure makes it compact so its good for storage as you can fit more into a small space
Describe the structure of Amylopectin
- A long branched chain of a-glucose
- Has lots of side branches
How does the structure of Amylopectin relate to its function?
Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily so glucose can be released quickly
What makes starch good for storage?
It is insoluble in water and doesn’t affect water potential, so it doesn’t cause water to enter cells via osmosis, which would make them swell
What is the function of Glycogen?
Animals use glycogen to store excess glucose
How does the structure of glycogen relate to its function?
- Has lots of side branches which means the glucose stored can be released quickly which is important for energy release in animals
- Compact so good for storage
What is the function of cellulose?
Provides structural support for cells (Eg. In plant cell walls)
Describe the structure of cellulose and how this relates to its function
- Made of long unbranched chains of beta-glucose
- When beta-glucose molecules bond, they form straight cellulose chains
- These chains are linked by hydrogen bonds to form strong fibres called microfibrils
- The strong fired mean cellulose provides structural support for cell walls
How would you test a substance to see if starches are present?
The iodine test
Describe how you would carry out the iodine test
- Add iodine dissolved in potassium iodide solution to the test sample
- If a starch Is present, the sample chains from browny-orange to a dark blue-black colour
How are glycogen and starches formed?
They are formed by the condensation of a-glucose molecules
