Carbohydrates

Question 1

What is a carbohydrate?

Answer 1

• molecules with the element oxygen, carbon and hydrogen

Question 2

What are reducing sugars?

Answer 2

• all monosaccharides are reducing sugars so they reduce Cu2+ ion which is blue to Cu+ ion which is red

Question 3

Give an example of a non reducing sugar

Answer 3

Sucrose

Question 4

What is the test for reducing sugars?

Answer 4

• Benedict’s reagent which is a copper sulfate solution
• add the same volume of Benedict’s solution as the sample
• if the sample isn’t a liquid, grind it or mix with water
• warm it gently in a water bath
• presence of a reducing sugar should show formation of brick red precipitate

Question 5

What is the test for non reducing sugars?

Answer 5

• boil the sample with dilute HCl
• this should hydrolyse the sucrose into fructose and glucose which are monosaccharides and so are reducing sugars
• then perform the normal test for reducing sugars

Question 6

Give example of the formation of dipeptides?

Answer 6

• alpha glucose + alpha glucose&raquo_space;> maltose
• glucose + galactose&raquo_space;> lactose
• glucose + fructose&raquo_space;> sucrose

Question 7

What are the two type of glucose monosaccharides and what is the difference between them two?

Answer 7

• alpha glucose… has hydroxyl group on bottom of first and fourth carbon
• beta glucose… has hydroxyl group on top on first carbon but still hydroxyl on bottom of fourth carbon

Question 8

What polysaccharide is formed from alpha glucose?

Answer 8

• starch in plants

- glycogen in animals

Question 9

What are the two different types of starch and what are the main differences between them?

Answer 9

• AMYLOSE..
• only 1,4-glycosidic bonds
• angles of these bonds causes the polysaccharide to twist into an alpha helix
• hydrogen bonds within the alpha helix to stabilise it and make it more compact
• AMYLOPECTIN
• 1,4 and 1,6 glycosidic bonds
• branched
• compact

Question 10

What features of amylopectin make it a good store of energy?

Answer 10

• many branches for the enzymes to act on to hydrolyse the polysaccharide chain for glucose molecules
• very compact so takes less space to store and a lot of energy can be stored within a small amount of space
• insoluble so does affect the water potential of plants

Question 11

What polysaccharide is formed from beta glucose and describe it

Answer 11

• CELLULOSE
• straight chain because every other beta glucose molecule has to be rotate 180 degrees
• cellulose polysaccharides are joined to each other via hydrogen bonds to form microfibrils
• these combine to form macrofibrils which then again combine to form fibres
• this is what makes up the cell wall

Question 12

How do monosaccharides combine?

Answer 12

• condensation reaction
• removal of water
• hydroxyl groups interact to form glycosidic bonds

Question 13

Describe the structure of glycogen

Answer 13

• 1,4 and 1,6 glycosidic bonds
• more branched than amylopectin
• more ends for enzymes to hydrolyse for glucose
• insoluble so doesn’t affect water potential
• compact so doesn’t need a lot of space top store which is more important for animals as they are more mobile