polysaccharides

Question 1

examples of polysaccharide

Answer 1

Starch and glycogen

Question 2

Structure of starch

Answer 2

polysaccharide made up of many alpha glucose molecules

There are two kinds of glycosidic bonds that can form between the glucose molecules
which allows two slightly different structural units to be formed:

Amylose and amylopectin

Question 3

Amylose

Answer 3

Amylose makes up 30% of starch

A long unbranched chain of α-glucose molecules connected by 1-4 glycosidic bonds only

It coils into a compact helix which is then held in place by hydrogen bonds

The OH groups are arranged to the inside of
the coil, making amylose less soluble as these are the groups that would H bond with water.

Question 4

Amylopectin

Answer 4

Amylopectin makes up 70% of starch

chains of α-glucose molecules connected by 1-4 glycosidic bonds to form helical shape

Approximately every 25 glucose units, a 1-6 glycosidic bond forms by condensation, creating a branch

This creates a highly branched structure

There are multiple sites for hydrolysis allowing glucose to be removed quickly.

Question 5

Glycogen

Answer 5

stored as small granules, particularly in muscles and the liver.

Used as an energy storage molecule by animals and fungi.

Structure:

Made of α-glucose.

Branch points in glycogen are due to 1-6 glycosidic bonds, occurring around every 10th residue.

coiled making it more compact for easier
storage.

Glycogen is a more highly branched molecule for easier access to the free ends where hydrolysis takes place. This means stored glucose can be released quickly.

Question 6

Structure suited for function

Answer 6

key properties of amylopectin and glycogen are that they are insoluble, branched, and compact.

The extensive branching means that more free ends are available for hydrolysis and
condensation reactions

Compaction is essential so that as many glucose units as possible are stored for future use.

Question 7

Why is it important that glucose is stored and not always freely available in blood or phloem?

Answer 7

Glucose is soluble, allowing it to dissolve in the blood. However, too much glucose will lower the water potential of the blood, causing water to move out of cells by osmosis.
This is why glucose must be stored in an insoluble form.

Question 8

Cellulose

Answer 8

Cellulose is made of long, unbranched chains of β glucose.

The hydroxyl groups on carbon 1 and carbon 4 of the two glucose molecules are too far apart.

Alternate beta glucose molecules must be inverted (180°).

Now the two are close enough to form a 1-4 β glycosidic bond.

No branches or coils - it is a straight chain molecule.

Question 9

adaptations of cellulose

Answer 9

Hydrogen bonds form between
the chains of cellulose molecules to
form microfibrils.
Microfibrils join together to form a macrofibril.
Many macrofibrils join to form fibres.
These have high tensile strength and are
insoluble.

Question 10

Function of cellulose

Answer 10

All plant cells have a cell wall, made from cellulose, to support the plant – high tensile strength.

Cellulose prevents cells from bursting when turgid and protects the cell membrane.

The cell wall is fully permeable due to space between macrofibrils.

Insoluble and inert

Question 11

Why is cellulose important to humans?

Answer 11

Cellulose is very hard to break down and so it forms fibre or roughage which is necessary for a healthy digestive system