Carbohydrates

Question 1

What are monosaccharides and what are they the building blocks for?

Answer 1

• They are small organic molecules

- They are building blocks for larger carbohydrates.

Question 2

What general formula do monosaccharides have?

Answer 2

(CH20)n

Question 3

What is a sugar called that has

A) three carbon atoms
B) five carbon atoms
C) six carbon atoms + type of sugar it is

Answer 3

A) triose
B) pentose
C) hexose which is a glucose sugar

Question 4

What is the general formula of hexose sugars?

Answer 4

C6H12O6

Question 5

What do all hexose sugars differ in?

Answer 5

Molecular structure

Question 6

What occurs when monosaccharides are dissolved in water and how can they alter their binding?

Answer 6

The carbon atoms of the monosaccharides make a ring.

They can alter their binding to make straight chains, with the rigs and chains in equilibrium.

Question 7

Name the two isomers of glucose and state what they are based on.

Answer 7

α-glucose and β-glucose and they are based on the positions of an (OH) and (H) of the molecule.

Question 8

What do the different forms of glucose result in and give example(s).

Answer 8

They result in biological differences when they form polymers, such as starch and cellulose.

Question 9

What is a monosaccharide (simple).

Answer 9

An individual sugar molecule.

Question 10

Monosaccharides have four main functions.

Describe them and give examples where possible.

Answer 10

1. A source of energy in respiration.

Carbon-hydrogen and carbon-carbon bonds are broken to release energy, which is transferred to make ATP.

2. Building blocks for larger molecules.

E.g. Glucose is used to make the polysaccharides starch, glycogen and cellulose.

3. Intermediates in reactions.

E.g. Trioses, are intermediates in the reactions of respiration and photosynthesis.

4. Constituents of nucleotides.

E.g. Deoxyribose in DNA, and ribose in RNA, ATP and ADP.

Question 11

What are disaccharides and described their formation.

Answer 11

• Disaccharides are composed of two monosaccharide units.

- They are bonded together with the formation of a condensation reaction.

Question 12

Describe (or draw) the formation of a glycosidic bond between two glucose molecules, making maltose.

Answer 12

α-glucose + α-glucose = maltose

• This is a condensation reaction.
• Water is being removed between C4 of one glucose molecule and C1 of the other.
• The bond formed between glucose molecules is a glucosidic bond.
• It is between C1 and C4, so it is called a 1, 4-glucosidic bond.
• Because the disaccharide molecule is straight and not twisted, the bond is an α-1, 4-glycosidic bond.

Question 13

Name three disaccharides, their component monosaccharides and their biological role.

Answer 13

Maltose:
glucose + glucose
germinating seeds

Sucrose:
glucose + fructose
transport in phloem of flowering plants

Lactose:
glucose + galactose
in mammalian milk

Question 14

What do reducing sugars include?

Answer 14

All monosaccharides and some disaccharides, e.g. Maltose.

Question 15

What are polysaccharides (detail).

Answer 15

They are large, complex polymers.

They are formed from dry large numbers of monosaccharide units, which are their monomers, linked by glucosidic bonds.

Question 16

What is glucose the main source for?

Answer 16

Energy in cells.

Question 17

Describe glucose when placed in water and a problem that occurs.

Also, how is this problem avoided?

Answer 17

It is soluble in water and the problem is, it would increase the concentration of the cell contents, and consequently draw water in by osmosis.

This problem is avoided by converting the glucose into a storage product, a polysaccharide, starch.

Question 18

Why is starch a useful storage form of glucose? (4 points)

Answer 18

1. It is insoluble so it has no osmotic effect.
2. It cannot diffuse out of the cell.
3. It is a compact molecule and can be stored in a small space.
4. It carries a lot of energy in its C-H and C-C bonds.

Question 19

What is starch and what is it made of?

What are the two different forms?

Answer 19

Starch is the main store of glucose for plants.

Starch grains are found in high concentrations in seeds and storage organs such as potato tubers.

Starch is made of α-glucose molecules in two different ways, found in two polymers:

• amylose
• amylopectin

Question 20

Describe the structure of amylose and state what is formed when the chain coils.

Answer 20

It is a linear, unbranded molecule with α-1, 4-glycosidic bonds forming between the first carbon atom (C1) on one glucose monomer and the fourth carbon atom (C4) on the adjacent one.

This is repeated, forming a chain, which coils into an α-helix.

Question 21

Describe the structure of amylopectin.

Answer 21

It has chains of glucose monomers joined with α-1, 4-glycosidic bonds.

They are cross-linked with α-1,6-glycosidic bonds and fit inside the amylose.

When a glycosidic bond forms between the C1 atom of one glucose molecule and the C6 atom on another, a side branch is seen.

α-1,4-glycosidic bonds continue on from the start of the branch.

Question 22

What are carbohydrates (in detail).

Answer 22

• Carbohydrates are organic compounds containing carbon, hydrogen and oxygen.
• The basic unit is a monosaccharide.
• Two basic units combine to from a disaccharide.
• And many basic units combine to form a polysaccharide.

Question 23

What is glycogen?

Answer 23

The main storage product in animals.

Question 24

What used to be called ‘animal starch’ and why?

Answer 24

Because it’s very similar to amylopectin.

Question 25

Give two points as to how glycogen is similar to amylopectin and give one difference between the two.

Answer 25

It has α-1,4 and α-1,6 bonds.

The difference is that glycogen molecules have shorter α-1,4-linked chains and so are more branded than amylopectin.

Question 26

What is cellulose? (Simple)

Answer 26

A structural polysaccharide.

Question 27

Describe (or draw) the structure of cellulose.

Answer 27

1. Cellulose consists of many long, parallel chains of β-glucose units.
2. The glucose monomers are joined by β-1,4-glycosidic bonds, and the β-link rotates adjacent glucose molecules by 180°.
3. This allows hydrogen bonds to form between the (OH) groups of adjacent parallel chains and contributes to cellulose’s structural stability.

Question 28

In terms or cellulose, describe the formation of micro fibrils and therefore fibers and the role this plays.

Answer 28

• between 60 and 70 cellulose molecules become tightly cross-linked to form bundles called microfibrils.
• the microfibrils are, in turn, held in bundles called fibers.
• a cell wall has several layers of fibers, which run parallel within a layer but at an angle to adjacent layers.
• this laminated structure contributes to the strength of the cell wall.

Question 29

Are cellulose fibres freely permeable or selectively permeable and why?

Answer 29

Cellulose fibres are freely permeable, because there are spaces between the fibres.

Water and its solutes can penetrate through these spaces in the cell wall, to the cell membrane.

Question 30

What is chitin (simple)

And where is it found?

Answer 30

A structural polysaccharide, found in the exoskeleton of insects and in fungal cell walls.

Question 31

Describe its structure and name a carbohydrate it’s similar to.

Answer 31

It resembles cellulose

With its long chains of β-1,4-linked monomers,

but has groups derived from amino acids added, to form a heteropolysaccharide.

Like cellulose, the monomers are rotated through 180° in rotation to their neighbors,

and the long parallel chains are cross-linked to each other by hydrogen bonds, forming microfibrils.

Question 32

Name three properties of Chitin

Answer 32

It is strong, waterproof and lightweight.

Question 33

How does Chitin differ from cellulose?

Answer 33

It has groups derived from amino acids added, to form a heteropolysaccharide.