B.4. Carbohydrates

Question 1

What functional groups do Monosaccharides contain?

Answer 1

+ Carbonyl group (>C=O)

+ At least 2 Hydroxyl groups (-OH)

Question 2

How do Monosaccharides differ?

Answer 2

In orientation of the hydroxyl group

Question 3

What happens to straight chain forms of sugars in solutions?

Answer 3

Cyclise to form ring structures containing an ether linkage.

Question 4

What does the ‘Haworth Projection’ represent ?

Answer 4

Cyclic structures of Monosaccharides that give the 3D perspectives.

Question 5

In glucose which carbon does the numbering start at?

Answer 5

The carbon of the carbonyl group (is C1)

Question 6

In Harworth Projection the groups that appear on the LHS of the straight chain = appear____the ring

Answer 6

Above

Question 7

In Harworth Projection the groups that appear on the RHS of the straight chain = appear____the ring

Answer 7

Below

Question 8

What is the difference between the structure of galactose and glucose?

Answer 8

The orientation of the H and OH around the C4

Question 9

How many chiral carbon atoms are there in glucose and galactose? and which are they?!

Answer 9

4
C2, C3, C4, C5
(C1 and C6 = non chiral!)

Question 10

Why do monosaccharides form rings?

Answer 10

Because the straight chain form is unstable due to the presence of a carbonyl group and several hydroxyl groups.

Question 11

Aldose

Answer 11

Aldehyde sugar

= when the carbonyl group of a monosaccharide is connected to the terminal C atom.

Question 12

Ketose

Answer 12

Ketone sugar

= When the carbonyl group of a monosaccharide is connected to the 2nd C.

Question 13

Disaccharides

Answer 13

2 simple sugars linked together with a glycosidic bond. C-O-C

Question 14

Which carbons usually from the glycosidic bond?

Answer 14

1,4

Question 15

Properties of Monosaccharides and Disaccharides (4)

Answer 15

1) Low Molar masses
2) Sweet
3) Readily Soluble in water
= because of H-bonding between water and the -OH groups
4) Readily taken up by cells

Question 16

Why do monosaccharides and disaccharides form crystalline solids?

Answer 16

Due to the INTRAmolecular H-bonds between the -OH groups

Question 17

Reducing sugars

Answer 17

Aldose Monosaccharides

= because Aldehydes are easily oxidised (to carboxylic acids)

Question 18

What do polysaccharides differ in? (4)

Answer 18

1) Nature of their recurring monosaccharides units
2) The bonds connecting the units
3) Length of their chain
4) Degree of branching

Question 19

Structure of starch amylose

Answer 19

+ straight chain joined by α-1,4 glycosidic bonds

+ coiled helix structure due to the intramolecular H-bonding of some -OH groups on diff glucose units

Question 20

Properties and function of starch amylose

Answer 20

+ Other -OH groups on outside form H-bonding w, water = making it somewhat water soluble
+ can be hydrolysed by amylase
+ stored as energy reserve

Question 21

Structure of starch amylopectin

Answer 21

+ α-1,4 linkages
+ branches formed by α-1,6 linkages of glucose
+ Interactions of water w, polymeric chains = restricted

Question 22

Properties and functions of starch amylopectin

Answer 22

+ INsoluble in water
+ can be hydrolysed by amylase
+ stored as energy reserve

Question 23

Structure of Cellulose

Answer 23

+ much longer chains
+ ALL glycosidic linkages in 1,4 position = LINEAR
+ Allows side-by-side alignment of cellulose chains = extensive H-bonding betw, chains = gives strength and rigidity
+ Can be hydrolysed by cellulase (absent in humans = unable to digest)
= Cows and many animals have bacteria that produce cellulase

Question 24

Properties and functions of Cellulose

Answer 24

+ structural component in plants
+ INsoluble in water due to extensive INTERmolecular H-bondings betw, chains
= not enough water molecules can H-bond w, cellulose to separate the chains
+ important dietary fibre