Carbohydrates

Question 1

What are the 2 types of sugars?

Answer 1

Reducing and Non-reducing sugars.

Question 2

What does it mean by a reducing sugar?

Answer 2

The molecule can freely donate electrons, the carbonyl group becomes oxidised.

Question 3

Name a non-reducing sugar

Answer 3

Sucrose.

Question 4

What is the molecular formula of glucose?

Answer 4

C6H12O6

Question 5

What are the 2 isomers of glucose?

Answer 5

Alpha-glucose and Beta-glucose.

Question 6

What is the difference between the alpha and beta glucose molecules?

Answer 6

In alpha-glucose, the hydroxyl group bonded to carbon 1 lies below the hydrogen molecule but in beta-glucose the hydroxyl group on carbon 1 lies above the hydrogen molecule.

Question 7

Name 3 different types of monosaccharides formed from molecules with varying number of C atoms

Answer 7

-Triose sugar
-Pentose sugar, e.g. ribose
-Hexose sugar, e.g. glucose

Question 8

What polysaccharides does start consist of?

Answer 8

Amylose and Amylopectin

Question 9

What are the monomer of starch?

Answer 9

Alpha-glucose

Question 10

What are the monomers of glycogen?

Answer 10

Alpha-glucose

Question 11

What are the monomers of cellulose?

Answer 11

Beta-glucose

Question 12

What is the reaction called that binds 2 monosaccharides together?

Answer 12

Condensation Reaction.

Question 13

What is the covalent bond called that is formed when 2 hydroxyl groups on different saccharides interact?

Answer 13

Glycosidic bond.

Question 14

What is removed when a glycosidic bond is formed?

Answer 14

A water molecule.

Question 15

What glycosidic bond is formed in maltose?

Answer 15

α-1,4 glycosidic bond.

Question 16

What glycosidic bond is formed in sucrose?

Answer 16

α-1,2 glycosidic bond.

Question 17

What glycosidic bonds are formed in amylopectin and glycogen?

Answer 17

α-1,4 glycosidic bond and α-1,6 glycosidic bond.

Question 18

What glycosidic bond is formed in cellulose?

Answer 18

β-1,4 glycosidic bond.

Question 19

How is the glycosidic bonds broken?

Answer 19

When water is added in a hydrolysis reaction.

Question 20

How is a sample tested for a non-reducing sugar, e.g. sucrose?

Answer 20

When sucrose is heated with hydrochloric acid this provides the water that hydrolyses the glycosidic bond resulting in two monosaccharides. An alkali is then added to neutralise the solution and then the Benedict’s test is done, giving a positive result.

Question 21

What do 2 monosaccharides form in a condensation reaction?

Answer 21

A disaccharide

Question 22

What monosaccharides are in lactose?

Answer 22

Alpha-glucose and galactose.

Question 23

What monosaccharides are in sucrose?

Answer 23

Alpha-glucose and fructose.

Question 24

Name 4 polysaccharides

Answer 24

-Cellulose
-Glycogen
-Amylose
-Amylopectin

Question 25

Describe the structure of amylose (energy store for plants).

Answer 25

Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules.

Question 26

Describe the structure of amylopectin (energy store for plants).

Answer 26

Branched chains with α-1,4 glycosidic bonds as well as α-1,6 glycosidic bonds.

Question 27

Describe the structure of glycogen (energy store for animals).

Answer 27

Highly branched molecule with α-1,4 glycosidic bonds as well as α-1,6 glycosidic bonds.

Question 28

Describe the structure of cellulose.

Answer 28

It consists of long chains of β-glucose joined together by 1,4 glycosidic bonds. However, in order to form the 1,4 glycosidic bonds consecutive β-glucose molecules must be rotated 180° (or alternated) to each other.

Question 29

What can form between opposing chains of cellulose and why?

Answer 29

Due to the inversion of the
β-glucose molecules, many hydrogen bonds form between the long chains giving cellulose its high tensile strength.

Question 30

Why are amylose and amylopectin a good storage molecule for plants?

Answer 30

Compact- the maximum number of glucose molecules are kept in the minimum amount of space, does not take up a lot of room in cells
Insoluble- no osmotic effect, unlike glucose which would lower the water potential of the cell.
Branched chain- The amylopectin in starch has branches that result in many terminal glucose molecules that can be easily hydrolysed for use during cellular respiration or added for storage.