Topic 1: polysaccharides

Question 1

Name the monomers of starch, glycogen and cellulose

Answer 1

starch: a-glucose
glycogen: a-glucose
cellulose: beta-glucose

Question 2

Which reaction and bonds join the monomers together to form starch, glycogen and cellulose?

Answer 2

Starch: Condensation
1,4 and 1,6-glycosidic bonds

glycogen: Condensation
1,4 and 1,6-glycosidic bonds

cellulose: Condensation 1,4-glycosidic bonds

Question 3

State the function of molecule (glycogen, starch, cellulose)

Answer 3

Starch: Glucose store (energy source)

Glycogen: Glucose store (energy source)

Cellulose: Provides structural strength

Question 4

State where the molecule is found (starch, glycogen and cellulose)

Answer 4

Starch: Starch grains in plant cells

Glycogen: In animals, mainly in the liver and muscle cells

Cellulose: In plants in the cell wall

Question 5

Describe the structure of starch

Answer 5

Starch is made up of amylose and amylopectin. Amylose monomers are joined by 1,4-glycosidic bonds resulting in a spiral-shaped polymer,
Amylopectin monomers are joined by 1,4 and 1,6-glycosidic bonds. The 1,6 glycosidic bonds result in branches.

Question 6

Describe the structure of glycogen

Answer 6

The key difference between the structure of glycogen and starch is that glycogen contains more 1,6- glycosidic bonds and is therefore more branched.

Question 7

Describe the structure of cellulose

Answer 7

Has long, straight chains of β- glucose. The parallel chains are held together by many hydrogen bonds, which collectively provide strength. This is called a fibril. Fibrils are held by hydrogen bonds to form a cellulose fibre.

Question 8

Explain how the structure of starch relates to function

Answer 8

Starch is insoluble due to the fact it is a large molecule. Therefore it will not change the water potential of a cell and cause osmosis to occur. The spiral shape means that it can be
readily compacted to store a lot. The branching strands provide a larger surface area for enzymes to attach to
increase hydrolysis.

Question 9

Explain how the structure of glycogen relates to function

Answer 9

Glycogen is insoluble due to the fact it is a large molecule so it will not change the water potential of a cell. Being highly branched provides a larger surface area for enzymes to attach. Glycogen is even more branched than starch, therefore it is hydrolysed back into glucose more
rapidly.

Question 10

Explain how the structure of cellulose relates to function

Answer 10

Cellulose is insoluble due to its large size. This is an advantage as it will not change the water potential of a cell and affect osmosis. Due to a large number of hydrogen bonds in and between the fibrils, cellulose is a very strong polysaccharide.