Carbohydrates

Question 1

What is the formula for monosaccharides?

Answer 1

Cn (H2O)n

Question 2

What are the examples of Triose?

Answer 2

Pyruvate and glyceraldehyde

Question 3

What are the examples of pentose?

Answer 3

Ribose and deoxyribose

Question 4

What is the difference between ribose and deoxyribose’s structures?

Answer 4

Deoxyribose has 1 less oxygen (thus deoxy = loss of oxygen)

Question 5

What are the examples of hexose?

Answer 5

Glucose, fructose and galactose

Question 6

What is the difference between alpha and beta glucose?

Answer 6

The oxygen and hydroxide molecules on C1 are switched with OH at the top in beta glucose (‘bouncing’ beta)

Question 7

What is a structural isomer?

Answer 7

Where molecules have the same formula but different structure

Question 8

What the three key properties of fructose?

Answer 8

• it is the main sugar in fruits/nectar
• very soluble
• sweeter than glucose

Question 9

What are the three key properties of galactose?

Answer 9

• important in glycolipid and glycoprotein production
• less soluble
• not as sweet as fructose

Question 10

What is the test for monosaccharides and what is it called?

Answer 10

The reducing sugars test.

• mix the test solution with an equal volume of Benedict’s solution
• heat (70oC)
• a positive test result is shown by the solution turning from blue to red

Question 11

What are disaccharides?

Answer 11

2 monosaccharides bonded by a glycosidic bond

Question 12

What type of reaction is the bond formation called and why?

Answer 12

Condensation reaction because water is released

Question 13

What the monosaccharides in maltose?

Answer 13

2 alpha glucose

Question 14

What are the monosaccharides in sucrose?

Answer 14

Alpha glucose and fructose

Question 15

What are the monosaccharides in lactose?

Answer 15

Beta glucose and galactose

Question 16

Where is maltose found?

Answer 16

Malt sugar

Question 17

Where is sucrose found?

Answer 17

Cane sugar

Question 18

Where is lactose found?

Answer 18

Milk sugar

Question 19

What is hydrolysis’ purpose in relativity to carbohydrates?

Answer 19

It is the splitting of the glycosidic bond by the chemical addition of a water molecule.
It enables disaccharides to be broken back down into mono (e.g in digestion)

Question 20

How can hydrolysis be increased?

Answer 20

Addition of acid and heat

Enzymes

Question 21

How does the non-reducing sugars (disaccharide) test work?

Answer 21

• add 2cm^3 to test tube
• add 10 drops HCl (1 mol)
• mix and heat (70oC)
• neutralise with alkali (sodium hydrogen carbonate)
• add 2cm^3 Bendict’s
• mix + heat
• change from blue to red = positive

Question 22

What is the main use of starch?

Answer 22

Main storage polysaccharide in plants

Question 23

What is the main use of glycogen?

Answer 23

Main storage polysaccharide in liver and muscles

Question 24

What is the main use of cellulose?

Answer 24

Main structural polysaccharide in plants

Question 25

What is the main use of chitin?

Answer 25

Main structural polysaccharide in insects

Question 26

What are polysaccharides?

Answer 26

Polymers made up of many monosaccharides joined by glycosidic bonds

Question 27

What polysaccharide group does alpha glucose contribute to?

Answer 27

Storage

Question 28

What polysaccharide group does beta glucose contribute to?

Answer 28

Structure

Question 29

What is amylose's structure and why is it good for glucose storage?

Answer 29

Un-branched long chain of alpha glucose with 1-4 bonds. The bond angles cause it to bend into a compact coiled helix which makes it really good for glucose storage.

Question 30

What is amylopectin's structure and why is it good for glucose storage?

Answer 30

Long branched chain with some 1-4 bonds but many more 1-6 that give it its branches. This enables easy access for enzymes to break down glycosidic bonds and release glucose.

Question 31

What percentage of starch is amylose?

Answer 31

20%

Question 32

What percentage of starch is amylopectin?

Answer 32

80%

Question 33

Why is starch and glycogen being insoluble beneficial?

Answer 33

It is a large molecule so it can't leave the cell via the membrane and has no osmotic effect (doesn't draw water into the cell)

Question 34

What is the test for starch?

Answer 34

Mix test solution with 3 drops of iodine solution. A change from orange to blue/black = positive result.

Question 35

What is glycogen's structure?

Answer 35

Similar to amylopectin but with many more 1-6 bonds leading to more side branches

Question 36

What is the effect of glycogen's many branches?

Answer 36

Stored glucose can be released quickly

Question 37

What is glycogen easily hydrolysed by?

Answer 37

Glycogen phosphorylase, an enzyme, to provide glucose for respiration

Question 38

How is cellulose structured?

Answer 38

Many beta glucose units linked by 1-4 glycosidic bonds forming long straight chains. Every other molecule rotates 180o so the hydroxyl (OH) groups line up. The alternating up and down bonds increases structural strength. The chains are cross linked by 3-6 hydrogen bonds.

Question 39

What is formed by the chains grouping in cellulose?

Answer 39

Strong fibres called microfibrils which make plant walls inelastic through their arrangement, giving strength and rigidity and preventing bursting when taking in excess water.

Question 40

Why can't enzymes that break down starch's glycosidic bonds break down cellulose's?

Answer 40

They cannot reach them, providing structural support

Question 41

What are chitin's properties and uses?

Answer 41

Strong, lightweight and waterproof. | Forms insect exoskeletons and is found in fungi cell walls.

Question 42

What is chitin's structure?

Answer 42

Similar to cellulose, but with some OH replaced by nitrogen containing acetylamine groups.

Question 43

What are carbohydrates' two main functions?

Answer 43

- energy source for plants and animals | - structural support for plants and insects.

Question 44

Why are disaccharides known as 'non-reducing sugars?'

Answer 44

They can't reduxe the blue copper sulfate in the Benedict's solution.