cellulose, glycogen and starch

Question 1

What is the animal version of starch?

Answer 1

glycogen

Question 2

Where is glycogen found?

Answer 2

in animals and bacteria

Question 3

Describe the structure of glycogen

Answer 3

Glycogen has a similar structure to amylopectin, containing many alpha 1–6 glycosidic bonds that produce an even more branched structure.

Question 4

What is the difference between the structure of glycogen and the structure of starch?

Answer 4

Glycogen have shorter chains and is more highly branched

Glycogen is less dense and more soluble than starch, and is broken down more rapidly. This indicates the higher metabolic requirements of animals compared with plants.

Question 5

Why is glycogen called “animal starch”?

Answer 5

because it is the major carbohydrate storage product of animals

Question 6

How is glycogen stored in animals?

Answer 6

as small granules mainly in the muscles and the liver

Question 7

Why is the mass of carbohydrate that is stored, relatively smaller in animals?

Answer 7

because fat is the main storage molecule in animals

Question 8

Why does Glycogen’s structure and properties, make it suitable for storage?

Answer 8

• it is insoluble and therefore does not tend to draw water into the cells by osmosis
• being insoluble, it does not diffuse out of cells
• it is compact, so a lot of it can be stored in a small space
• more highly branched than starch and so has more ends that can be acted on simultaneously by enzymes. hence, more rapidly broken down to form glucose monomers, which are used in respiration - important to animals, which have a higher metabolic rate and therefore respiratory rate than plants because they are more active.

Question 9

What type of molecule is cellulose, what makes it different from glucose and what is its properties as a result of this?

Answer 9

Polysaccharide, also a polymer of glucose, but the bonding between the glucose unit is different, making the cellulose molecules are long and straight.

Question 10

In what major way does cellulose differ from glycogen and starch?

Answer 10

made up of beta glucose instead of alpha glucose

Question 11

Describe the structure of cellulose

Answer 11

it has straight, unbranched chains, which run parallel to one another,

allowing hydrogen bonds to form cross-linkages between adjacent chains, which add collective strength.

these molecules are grouped to form microfibrils which in turn are grouped to form fibres all of which provide yet more strength

Ever second beta glucose is rotated

Question 12

How are cellulose molecules arranged and what bonds are they held together by?

Answer 12

Arranged side by side to form microfibrils and held together by many weak hydrogen bonds.

Question 13

Even though hydrogen bonds are individually weak, why do they still make a considerable contribution to strengthening cellulose?

Answer 13

Because the sheer overall number of them adds to the strength

Question 14

Where is cellulose found and how does its structure help?

Answer 14

Plants - strengthen the plant cell wall

Question 15

What is the role of the cell wall?

Answer 15

• provides rigidity
• also prevent the plant cell from bursting as water enters it by osmosis

Question 16

How does the cell wall prevent the plant cell from bursting?

Answer 16

it exerts an inward pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another making non-woody parts o the plant semi-rigid

Question 17

Why is it important that stems and leaves maintain their turgid state?

Answer 17

so that they can provide the maximum surface area for photosynthesis

Question 18

What are lipids and what do they contain?

Answer 18

Oils and fats. Contain carbon, hydrogen and oxygen

Question 19

What are the properties of lipids?

Answer 19

insoluble in water

are soluble in organic solvents such as alcohols and acetone

Question 20

What group of lipids are plant oils and animal fats mostly made up of?

Answer 20

triglycerides

Question 21

Starch is a store of glucose. What happens when glucose is needed by the plant cell? Why is the process to obtain glucose from the starch quick?

Answer 21

water is used to break the glycosidic bonds (hydrolysis reaction).

This is done quickly because the enzymes that break down starch act at the ends of the molecules.

Since amylopectin has a lot of branches, it has a lot of ends, allowing the enzymes to break down starch rapidly

Question 22

How is starch adapted for its main role, energy storage?

Answer 22

its insoluble and therefore doesn’t affect water potential, so water is not drawn into the cells by osmosis

being large and insoluble, it does not diffuse out of cells

its compact, so a lot of it can be stored in a small space

when hydrolysed it forms alpha glucose, which is both easily transported and readily used in respiration

the branched form has many ends, each of which can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly

Question 23

What makes starch molecules very compact

Answer 23

the unbranched chain in the structure, which is wound into a tight coil that makes the molecule very compact.

Question 24

What type of molecule is starch and where is it only found and in what form?

Answer 24

It is a polysaccharide only found in plants in small grains - intracellular grains in organelles called plastids

Question 25

What properties of starch molecules make it ideal for storing glucose?

Answer 25

They are insoluble and compact

Question 26

Describe the properties of amylopectin

Answer 26

It is soluble in both hot and cold water

It does not resist digestion

It shows extensive branching

It gives reddish-brown color with iodine solution

Question 27

Describe the structure of amylopectin

Answer 27

A
polymer of alpha glycose joined by 1-4 glycosidic bonds

has a branch every 25-30 alpha glucose molecule. This branch is connected to the main chain by a glycosidic bond but between carbon 1 of an alpha molecule and carbon 6 of another one (1 6 glycosidic bond)

Question 28

Describe the properties of the amylose component of starch (mention something about its coiled structure

Answer 28

It is insoluble in cold water

It is more resistant to digestion due to packed helical structure

It limits the infiltration of water in starch

It gives dark blue/black color with iodine solution

Angles of the glycosidic bonds = coiled structure → makes it compact = can fit more into a small space (= good for storage)

Question 29

Describe the structure of amylose

Answer 29

polymer of alpha glucose molecules

compact cylindrical polysaccharide

Glycosidic bond linking the α-glucose molecules is an α-1,4 glycosidic bond.

Twisted into a complex helix with hydrogen bonds forming between glucose molecules along the chain