2.1.2 d-g Biological Molecules - Carbohydrates

Question 1

What are the elements present in Carbohydrates?

Answer 1

C , H, O

Question 2

Define monosaccharide

Answer 2

a single sugar molecule
monomers of carbohydrates

Question 3

Define Disaccharide

Answer 3

a molecule made of 2 monosaccharides joined by a glycosidic bond

Question 4

Define polysaccharide

Answer 4

a polymer made up of more than 2 monosaccharides joined together

Question 5

Define pentose sugar

Answer 5

a monosaccharide made up of 5 carbons

Question 6

Define hexose sugar

Answer 6

a monosaccharide made up of 6 carbons

Question 7

Define triose sugar and give an example

Answer 7

a monosaccharide made up of 3 carbons
- glyceraldehyde

Question 8

What a furanose ring?

Answer 8

a 5 membered ring
e.g. fructose

Question 9

What is a pyranose ring?

Answer 9

a 6 membered ring
e.g. glucose

Question 10

Draw a molecule of alpha-glucose

Answer 10

hexose
OH group on carbon 1 below the ring

Question 11

Draw a molecule of beta-glucose

Answer 11

hexose
OH group on carbon 1 above the ring

Question 12

Draw a molecule of ribose

Answer 12

pentose - 5 carbon atoms

Question 13

Define isomer

Answer 13

molecules with the same molecular formulae but different structural formulae

Question 14

What is the difference between alpha and beta glucose?

Answer 14

The hydrogen and hydroxyl groups on carbon 1 are reversed

Question 15

What is the difference between alpha glucose and ribose

Answer 15

• glucose is a pyranose/hexose
• ribose is a furanose/pentose
• glucose is used in starch and glycogen
• ribose is used in RNA

Question 16

What is the difference between alpha glucose and ribose

Answer 16

• glucose is a pyranose/hexose
• ribose is a furanose/pentose
• glucose is used in starch and glycogen
• ribose is used in RNA

Question 17

Give 3 examples of disaccharides and state which monosaccharides they are composed of

Answer 17

Maltose - alpha glucose + alpha glucose
Sucrose - alpha glucose + fructose
Lactose - alpha glucose + galactose

Question 18

State the functions and properties of glucose and where it is found

Answer 18

-monosaccharide
- used in respiration
- used to make polymers like starch, glycogen, cellulose

Question 19

State the functions and properties of fructose and where it is found

Answer 19

• hexose sugar
• found in fruit

Question 20

State the functions and properties of galactose

Answer 20

• hexose sugar

Question 21

Draw a labelled diagram demonstrating how two molecules of glucose form a disaccharide in a condensation reaction, showing the location of a 1,4-glycosidic bond and from where a water molecule is generated

Answer 21

condensation reaction
- hydroxyl groups on carbon 1 and 4
water is lost and bond is formed by remaining oxygen atom

Question 22

Describe, using a diagram, how hydrolysis of maltose occurs and why water is needed

Answer 22

• the glycosidic bond is broken by adding water
• catalysed by enzymes at 35-40 degrees celsius/ or by being boiled with an acid for acid hydrolysis

Question 23

Why does alpha-glucose link together to form starch but beta-glucose links together to form cellulose

Answer 23

because of the arrangement of the hydrogen and OH groups on carbon 1

Question 24

What are the two polysaccharides that make up starch?

Answer 24

• amylose (1,4 bonds only - bc unbranched)
• amylopectin ( 1,4 and 1,6 - bc branches and straight)

Question 25

Explain with use of diagrams why glycosidic bonds are called 1,4 or 1,6

Answer 25

depends on whether the glycosidic bonds between the OH groups on carbons 1 and 4 or 1 and 6.

Question 26

What is the structure of a cellulose fibre?

Answer 26

Cellulose chains link via hydrogen bonds
- forming strong fibres - called microfibrils
- microfibrils give structural support for cells

Question 27

Describe and explain the properties and functions of starch.

Answer 27

STARCH: stores excess glucose in plants
- made up of amylose and amylopectin
- coils into helix
- insoluble (no effect on water potential) + compact - ideal for storage
- amylose - straight, unbranched (1,4 a glucose)
- amylopectin - long branched (1,4 + 1,6 a glucose)
- amylopectin side branches - allow enzymes to hydrolyse into glucose
quickly

Question 28

Describe and explain the properties and functions of glycogen.

Answer 28

GLYCOGEN: polysaccharide - stores excess glucose in animals + fungi
- coils into helix
- insoluble (no effect on water potential) + compact - ideal for storage
- similar to amylopectin but v. more branched
- 1,4 + 1,6 a-glycosidic bonds = branched
- more branches - hydroylsed into glucose faster - glucose released quicker - meet high metabolic demands of animals

Question 29

Describe and explain the properties and functions of cellulose.

Answer 29

CELLULOSE: makes up cell wall in plants
- long straight
- insoluble (doesnt effect water potential) (permeable to solutes)
- unbranched chains of beta glucose
- doesnt form helix
- forms cellulose molecules from b-glucose which join via hydrogen bonds to form layers of microfibrils
- give strength to cell walls