3.3 Carbohydrates

Question 1

What are carbohydrates?

Answer 1

Molecules

consisting of carbon hydrogen & oxygen only

Question 2

What is a monosaccharide?

Answer 2

a single sugar molecule

Question 3

3.3 Carbohydrates

What are sugars?

Answer 3

Type of molecule

used by organisms as source of ATP/metabolic energy

Question 4

What is a glycosidic bond?

Answer 4

Covalent bond

between 2 monosaccharides

Question 5

What is a disaccharide?

Answer 5

2 sugars

joined by glycosidic bond

Question 6

What are examples of monosaccharides?

Answer 6

Glucose

Fructose

Galactose

Question 7

What are examples of disaccharides?

Answer 7

Maltose

Sucrose

Lactose

Question 8

What is a condensation reaction?

Answer 8

Reaction between 2 molecules

forming a larger molecule + releasing water molecule

Question 9

What is the name of the reaction by which glucose monomers join to form maltose?

Answer 9

condensation

Question 10

What is a hydrolysis reaction?

Answer 10

Breakdown of molecule

into 2 smaller molecules

by addition of water

Question 11

Draw the structure of an alpha-glucose molecule:

Answer 11

OH/hydroxyl group on carbon 1 is below the plane of carbon atoms

Question 12

Draw the structure of a beta glucose molecule:

Answer 12

OH/hydroxyl on carbon 1 is above plane of carbon atoms

Question 13

What is the difference between alpha & beta glucose?

Answer 13

OH on carbon 1 is above the plane in beta glucose

OH on carbon 1 is below plane in alpha glucose

Question 14

Name 3 examples of polysaccharide energy stores:

Answer 14

Glycogen

Starch: Amylopectin + Amylose

Question 15

What is the monomer of glycogen?

Answer 15

alpha glucose

Question 16

What is the monomer of starch?

Answer 16

alpha glucose

Question 17

What are the characteristics of an efficient energy store?

Answer 17

• BRANCHED
  
  • more ends for enzymes to bind & hydrolyse carbohydrate
• INSOLUBLE
  
  • does not dissolve & change water potential, causing unwanted osmosis
• COMPACT
  
  • can store high amounts of energy in limited space

Question 18

What is the energy store which animals & fungi use?

Answer 18

glycogen

Question 19

Where do animals store glycogen?

Answer 19

liver & muscle cells

Question 20

Where do plants store starch?

Answer 20

starch grains

Question 21

Compare the structures of glycogen & starch:

Answer 21

• GLYCOGEN
  
  • 1-4, more 1-6 glycodisic bonds than amylopectin
    
    • more branches & more compact than amylopectin
    • more ends for enzymes to hydrolyse into glucose at faster rate
      
      • higher metabolic demand of animals compared to plants
• AMYLOPECTIN
  
  • 1-4, less 1-6 glycosidic bonds than glycogen
  • less branches & less compact than glycogen
  • less ends for enzymes to hydrolyse into glucose, ∴ slower rate
    
    • lower metabolic demand of plants compared to animals
• AMYLOSE
  
  • 1-4 glycosidic bonds only
  • no branching
  • hydrogen bonds between ꭤ-glucoses form helix structure

Question 22

How is the demand for energy of plants & animals reflected in the structure of their energy stores?

Answer 22

Glycogen (energy store in animals) contains many more 1-6 glycosidic bonds than amylose/amylopectin

more branched & compact

more ends for enzymes to hydrolyse glycogen into glucose at faster rate

due to higher metabolic demand in animals compared to plants

Question 23

What is the monomer of cellulose?

Answer 23

beta-glucose

Question 24

Describe the structure of cellulose:

Answer 24

straight chained

each alternate beta-glucose molecule is inverted

1-4 glycosidic bonds

(otherwise OH on neighbouring glucose molecules would be too far away to react)

strong & insoluble

Question 25

Describe how cellulose chains join to form cell walls:

Answer 25

beta-glucose undergo condensation to form straight-chain cellulose polymers with 1-4 glycosidic bonds

hydrogen bonds form between cellulose chains, forming microfibrils

microfibrils join to form macrofibrils

Question 26

Describe the properties of cellulose:

Answer 26

strong & insoluble