AQA AS Biology Unit 2: Polysaccharides

HideShow resource information
  • Created by: LucySPG
  • Created on: 22-08-13 17:14
Preview of AQA AS Biology Unit 2: Polysaccharides

First 73 words of the document:

Polysaccharides
Polysaccharides are substances whose molecules are polymers made of many sugars.
They are formed by combining together many monosaccharide molecules.
This process is called a condensation reaction.
The monosaccharides are joined together by glycosidic bonds.
As polysaccharides are very large molecules, they are insoluble.
This makes them very suitable for storage.
When they are hydrolysed, polysaccharides break down into disaccharides or
monosaccharides.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Starch
Starch is a polysaccharide found in many parts of a plant in the form of small grains.
Plants store excess glucose as starch and when a plant needs more glucose for energy it
breaks down the starch down to release glucose.
Especially large amounts occur in seeds and storage organs, such as potato tubers.
It forms an important component of food and is the major energy source in most diets.…read more

Page 3

Preview of page 3

Here's a taster:

Glycogen
Animal cells get energy from glucose too.
But animals store excess glucose as glycogen ­ a polysaccharide of a-glucose.
Glycogen is the major carbohydrate storage product of animals.
In animals it is stored as small granules mainly in the muscles and in the liver.
Glycogen is very similar in structure to starch but has shorter chains and is more highly
branched.
More branches means that stored glucose can be released quickly, which is
important for energy release in animals.…read more

Page 4

Preview of page 4

Here's a taster:

Cellulose
Cellulose is made of monomers of B-glucose.
The bonds between the sugars are straight so the cellulose chains are straight.
This is because in the B-glucose units, the positions of the ­H group and the ­ OH group is
on a single carbon atom are reversed.
In B-glucose the ­ OH group is above, rather than below, the ring.
This means that to form the glycosidic links, each B-glucose molecule must be rotated 180
compared to its neighbour.…read more

Page 5

Preview of page 5

Here's a taster:

Role of Cellulose
Cellulose is a major component of plant cell walls and provides rigidity to the plant
cell.
The cellulose cell wall also prevents the cell from bursting as water enters it by
osmosis.
It does this by exerting an outward pressure that stops any further influx of
water.
As a result, living plant cells are turgid and push against one another, making
herbaceous parts of the plant semi-rigid.…read more

Page 6

Preview of page 6

Here's a taster:

Starch and Glycogen Cellulose
A-glucose B-glucose
A glycosidic bonds B glycosidic bonds
H bonds within each chain H bonds between each chain
Forms helix Forms microfibrils
Can form H- bonds with water so soluble Can't form H-bonds with water so insoluble
Reacts with iodine to form purple complex Doesn't react with iodine
Easy to digest Difficult to digest
Storage role Structural role…read more

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »