Starch, Glycogen and Cellulose

Question 1

Where is starch found and in what form?

Answer 1

Starch is found in plants (leaves, stems etc), in the form of small granules or grains

Question 2

What is starch made up of?

Answer 2

Starch is made formed from two glucose polymers, amylose and amylopectin. Fundamentally formed from alpha glucose

Question 3

What is amylose?

Answer 3

Amylose is a glucose polymer formed from alpha glucose monomers, consisting of 1,4 glycosidic bonds

Question 4

Describe amylose’s structure

Answer 4

Amylose has an unbranched helical structure

Question 5

How does amylose’s structure help with its functions?

Answer 5

Amylose’s unbranched helical structure allows starch to store a lot of glucose in a small space

Question 6

What is amylopectin?

Answer 6

Amylopectin is an alpha glucose polymer consisting of (1,4) and (1,6) glycosidic bonds

Question 7

Describe amylopectin’s structure

Answer 7

Amylopectin has a branched structure consisting of (1,4) and (1,6) glycosidic bonds

Question 8

How does amylopectins structure help with its function?

Answer 8

Amylopectin has a branched structure that increases its surface area to volume ratio and ensures the rapid hydrolysis of starch into glucose, to be easily transported and readily used in respiration

Question 9

Glucose is converted into starch for storage within plant cells

Describe the reaction that occurs for this to happen

Answer 9

Many alpha glucose monomers are joined together through multiple condensation reactions. Each reaction involving the removal of a water molecule and the formation of (1,4) and (1,6) glycosidic bonds

Question 10

What is starch composed of that affects its structure and how does this structure help with starch’s function?

Answer 10

Starch is composed of amylose and amylopectin.

Amylose has an unbranched, helical structure which allows for the storage of many glucose molecules within a small area, making starch a more compact molecule.

Amylopectin has a highly branched structure which increases the surface area to volume ratio and ensures the rapid hydrolysis of starch into glucose, to be easily transported and readily used in respiration

Question 11

How much amylose and amylopectin make up starch (percentages)?

Answer 11

Amylose makes up to 10-30% of starch

Amylopectin makes up to 70-90% of starch

Question 12

Starch is a carbohydrate often stored in plant cells. Describe and explain two features of starch that make it a good storage molecule

Answer 12

1. It is insoluble molecule so it does not affect water potential, so water is not drawn into the cells by osmosis
2. It is large + insoluble, so it does not diffuse out of cells

Question 13

Where is glycogen mainly found and how is it stored?

Answer 13

Glycogen is found in animal cells, mainly in the muscles/liver, stored as small granules

Question 14

Why is glycogen broken down more rapidly than starch?

Answer 14

Because its highly branched structure has more ends for enzymes to act on, producing glucose quickly

Question 15

Describe glycogen’s structure

Answer 15

Glycogen has a highly branched structure, even more branched than amylopectin

Question 16

How does glycogen’s structure help with its function? Why is its structure important in animals?

Answer 16

Glycogen’s highly branched structure increases the surface area to volume ratio, allowing enzymes to act more efficiently and produce glucose quickly. This is important for animals as they move a lot and require more energy in smaller amounts of time. Additionally, the increased surface area allows glycogen to reach all respiring tissues within the animal

Question 17

Why is glycogen well - suited for storage? (2 reasons)

Answer 17

1. It is insoluble so it does not draw water into cells by osmosis and does not diffuse of cells
2. It is highly branched so more ends can be acted on simultaneously by enzymes for rapid glucose release

Question 18

What is cellulose?

Answer 18

Cellulose is a beta glucose polysaccharide. Consisting of (1,4) glycosidic bonds

Question 19

How does cellulose form its glycosidic bonds between its beta glucose monomers?

Answer 19

Cellulose forms its glycosidic bonds between the beta glucose monomers through multiple condensation reactions. The beta glucose monomers must be rotated 180 degrees opposite to each other, prior to these reactions

Question 20

Where is cellulose found?

Answer 20

Cellulose is found in plants cells, specifically their cell walls

Question 21

Describe cellulose’s structure

Answer 21

Cellulose is composed of beta glucose monomers which form long, straight chains which are held in parallel to each other by hydrogen bonds forming fibrils

Question 22

Glycogen and cellulose are both carbohydrates. Describe two differences between the structure of a cellulose molecule and glycogen molecule

Answer 22

1. Cellulose is made up of beta glucose molecules and glycogen is made from alpha glucose molecules
2. Cellulose has long straight chains and glycogen has a branched structure
3. Glycogen has (1,4) and (1,6) glycosidic bonds and cellulose only has (1,4) glycosidic bonds

Question 23

How is cellulose’s structure suited to its function? (2pts)

Answer 23

1. It is made of beta glucose which produces long, straight, unbranched chains
2. Molecules group into microfibrils and fibres to produce extra strength

Question 24

How does cellulose prevent plant cells from bursting?

Answer 24

The cell wall exerts inward pressure, limiting water uptake by osmosis

Question 25

Starch and cellulose are two important plant polysaccharides Describe the difference in structure of the starch molecule and the cellulose molecule

Answer 25

1. Starch has a helical structure whereas cellulose has long, straight chains forming its structure 2. Starch is composed of (1,4) and (1,6) glycosidic bonds whereas cellulose is composed of just (1,4) glycosidic bonds