S1-starch,glycogen and cellulose Flashcards
1
Q
What is starch and how is it formed?
A
- A polysaccharide.
- Found in plants.
- Formed by joining 200-100,000 a-glucose monosaccharides in condensation reactions forming glcosidic bonds.
- Major energy source.
- Main role is storage.
- Found in plant cells.
- Never found in animal cells.
2
Q
What is the test for starch?
A
- Add 2 drops of iodine to a 2cm^3csample.
- Shake or stir
Positive test=blue-black
3
Q
Describe the 2 structures of starch.
A
- Branched or unbranched chains.
* Unbranched wound into helical chains.
4
Q
How is starch adapted for its function?
A
- Insoluble- doesn’t affect water potential- water not drawn into cells via osmosis
- Large and insoluble - doesn’t diffuse out of cells
- Compact- can store a lot in a small space.
- When hydrolysed forms a-glucose- easily transported and ready for respiration.
- The branched form has many ends- enzymes can act on each end simultaneously- glucose released rapidly.
5
Q
Where is glycogen found?
A
In animal and bacteria cells.
6
Q
Describe glycogens structure
A
Like starch but shorter chains and more highly branched.
7
Q
How is glycogen stored in animals?
A
- Small granules
* Mostly in muscles and liver
8
Q
How is glycogen adapted to its function?
A
- Insoluble- doesn’t affect water potential- water not drawn into cells via osmosis
- Large and insoluble - doesn’t diffuse out of cells
- Compact- can store a lot in a small space.
- Highly branched (more than starch) - enzymes can act on each end simultaneously- glucose monomers released rapidly- ready for respiration.
9
Q
What is the structure of cellulose?
A
- Polysaccharide
- Made from B-glucose
- Straight unbranched chains
- Chains run parallel to each other
- Hydrogen bonds form cross-linkages between adjacent chains
- Each hydrogen bond alone is week-together they are strong
10
Q
Describe the forms of cellulose
A
- Cellulose molecules grouped together to form microfibrils
* Microfibrils arranged in parallel groups-fibres
11
Q
What is cellulose used for?
A
- Major component of cell walls-provides cell rigidity
- Cellulose cell walls prevents bursting from osmosis
- Exerts inwards pressure-stops further influx of water
12
Q
How is cellulose suited to provide support and rigidity?
A
- Made up of B-glucose- so form straight, unbranched chains
- Hydrogen bonds between chains add collective strength
- Grouped as microfibrils-grouped as fibres-provides more strength
