carbohydrates ( polysaccharides )

Question 1

what are polysaccharides?

Answer 1

polysaccharides are large polymers of monosaccharide molecules

Question 2

name three polysaccharides

Answer 2

cellulose, starch and glycogen

Question 3

how are cellulose, starch and glycogen formed?

Answer 3

they are polymers of glucose and are formed by the joining of glucose molecules during condensation reactions

Question 4

how do polysaccharides differ and what is their function?

Answer 4

polysaccharides differ in the number and arrangement of the glucose molecules they contain. they function as storage or structural molecules.

Question 5

are polysaccharides reducing or non reducing?

Answer 5

non reducing - giving a negative result in the benedict’s test

Question 6

what are some properties of polysaccharides?

Answer 6

they are unsweet to taste and relatively insoluble in water

Question 7

what is cellulose?

Answer 7

cellulose is a fibrous polysaccharide found in the cell wall of plants, which provide rigidity and shape to the cell

Question 8

draw the structure of beta glucose

Answer 8

see diagram

Question 9

how is cellulose formed and what is it formed from?

Answer 9

cellulose is a polysaccharide of beta glucose molecules joined together by glycosidic bonds. these bonds are formed in condensation reactions to form a long, straight chain. cellulose is made up of a single type of polymer, this is because only a single type of glycosidic bond is possible (beta 1,4 glycosidic bond).

Question 10

what does the beta 1,4 glycosidic bond form?

Answer 10

it causes every other beta glucose monomer to invert

Question 11

what is the structure of cellulose in the cell wall?

Answer 11

hydroxyl (OH) groups which project from either side of the beta glucose chain form hydrogen bonds with the hydroxyl (OH) groups of other adjacent chains producing a three dimensional structure known as a microfibril.
microfibrils are grouped together in larger bundles known as macrofibrils.
macrofibrils in one layer are oriented in the same direction.
macrofibrils in successive layers are oriented in a different direction.
macrofibrils of these different layers are interwoven, and embedded in a matrix providing rigidity.
the cellulose cell wall is usually fully permeable due to minute channels between the different layers of macrofibrils.

Question 12

what is starch?

Answer 12

starch is the storage carbohydrate found in plants, consisting of long, branched chains of alpha glucose molecules

Question 13

what polymers make up starch?

Answer 13

amylose, which is the result of alpha 1,4 glycosidic bonds and amylopectin, which is the result of both alpha 1,4 and alpha 1,6 glycosidic bonds

Question 14

where is starch stored?

Answer 14

starch is stored in starch grains (amyloplasts) in the cytoplasm

Question 15

how is starch suited to it’s function as a storage compound?

Answer 15

it is insoluble and therefore osmotically inactive (doesn’t draw water in by osmosis which could lead to cell damage).
the molecule has a helical shape forming a compact store.

Question 16

why is starch branched and what is the benefit of this?

Answer 16

starch is branched as a result of alpha 1,6 glycosidic bonds and the benefit is that there’s more free ends for enzymes to attach to

Question 17

how is starch hydrolysed?

Answer 17

starch is hydrolysed by the enzyme amylase to produce the disaccharide maltose

Question 18

how do you test for the presence of starch?

Answer 18

starch can be detected in a sample by using the iodine test. add 2-3 drops of iodine solution. if starch is present a blue/black colour is produced. if no starch is present the iodine solution remains orange/yellow.

Question 19

what is glycogen?

Answer 19

glycogen is the storage carbohydrate found in the cytoplasm of animal cells. it is sometimes referred to as ‘animal starch’ due to similarities in structure and function between the two molecules.

Question 20

what is glycogen a polymer of and how does this differ to starch?

Answer 20

glycogen is a polymer of alpha glucose, similar to starch but with more branches (free ends), which means it can be hydrolysed rapidly to release glucose for respiration

Question 21

what properties of glycogen make it a suitable storage compound?

Answer 21

it is insoluble and osmotically inactive, like starch

Question 22

where is glycogen found?

Answer 22

it is stored in large amounts in liver and muscle tissues