Lecture 4 - Carbohydrates

Question 1

What are saccharides

Answer 1

1. Make up nearly 50% dry weight of cells
2. Often described with the prefix Glyco
3. And suffix -ose
4. Originally compounds of the formula CnH2nOn

Question 2

What are the functions of saccharides

Answer 2

1. Metabolic energy source
2. Structural component in cell wall and extracellular matrix
3. Recognition sites on cell surfaces- for adhesion and signalling

Question 3

What are glycoconjugates

Answer 3

1. General classification for carbohydrates covalently linked with other chemical species
2. Glycoconjugates are formed via glycosylation
3. Modify solubility, stability and life span

Question 4

What are 4 examples of glycoconjugates

Answer 4

1. Glycoproteins
2. Proteoglycans
3. Glycolipids
4. Oligosaccharides

Question 5

What are the 4 classes of saccharide

Answer 5

1. Monosaccharide
2. Oligosaccharide
3. Polysaccharide
4. Monosaccharide derivatives

Question 6

What is a monosaccharide

Answer 6

1. Sugars which cannot be hydrolysed to give a simple sugar
2. e.g. Fructose

Question 7

What is an oligosaccharide

Answer 7

1. A carbohydrate which is composed of a small number of monosaccharide units (2-3)

Question 8

What is a polysaccharide

Answer 8

1. A carbohydrate whose molecules consist of a number of sugar molecules bonded together
2. They range in structure from linear to highly branched
3. E.g starch, cellulose, glycogen

Question 9

What are examples of monosaccharide derivatives

Answer 9

1. sugar acids
2. Sugar alcohols
3. Alditols
4. Amino sugars
5. Deoxysugars
6. L-ascorbic acid
7. Sugar phosphates

Question 10

What is an aldose

Answer 10

1. A monosaccharide which contains an aldehyde

Question 11

What is a ketose

Answer 11

1. A monosaccharide which contains a ketone
2. Can also use the suffix -ulose instead of -ose

Question 12

What is the simplest unit of a sugar

Answer 12

1. Glyceraldehyde
2. Not sugar itself- what they are built up from
3. Contains chiral carbon
   4.

Question 13

How do you draw Fischer projections

Answer 13

1. Line longest chain down sheet of paper
2. All molecules drawn in plain of paper
3. But actually Side chains are coming out towards us.
4. D means first hydroxyl up on chain is on right
5. If L every side chain is swapped

Question 14

What is an anomeric position

Answer 14

1. An anomeric carbon can be identified as the carbonyl carbon (of the aldehyde or ketone functional group) in the open-chain form of the sugar.

Question 15

What form do sugars naturally exist

Answer 15

1. Aldoess and ketoses (reducing sugars) can cyclise
2. Pentoses (furanose) and hexoses (pyranose) particularly favoured

Question 16

What is the Haworth representation

Answer 16

1. Represents the cyclic structure of a saccharide
2. Side groups point up or down
3. Hemiacetal- OH reacts with aldehyde- forms C1- anomeric centre
4. 1 O in the ring

Question 17

What is the Mills representation

Answer 17

1. Ring
2. Shows OH groups with dash/wedged bonds
3. In alpha glucose anomeric OH is coming out, then alternate dash and wedge for rest

Question 18

What is chair representations

Answer 18

1. Chair like configuration
   2.

Question 19

Describe glucose chair like configuration when anomeric position is in beta form

Answer 19

1. All OH groups are equatorial
2. Anomeric position OH is pointing up and equatorial
3. Pyran ring- 6 membered
4. Beta-D-glucopyranose

Question 20

Describe glucose chair like configuration when anomeric position is in the alpha form

Answer 20

1. OH in anomeric position is axial pointing down
2. Alpha-D-glucopyranose
3. Alpha OH always pointing down

Question 21

What happens to the 5 position OH

Answer 21

1. CH2OH is opposite to side to what the 5OH would have been

Question 22

How is the hemiacetal formed

Answer 22

1. Reversible reaction with water
2. R-C=O (R-C=OH+)reacts with HO-R
3. Aldehyde is protonated -

Question 23

What are the 5 forms of glucose in order of most common

Answer 23

1. Beta-pyranose- most common
2. Alpha-pyranose
3. Beta-furanose
4. Alpha-furanose
5. open ring

Question 24

Describe order of frequency of the forms of glucose

Answer 24

1. Alpha-pyranose is less common than beta as has axial hydroxide group- less stable
2. Is more common than expected due to anomeric effect
3. 6-Membered rings are more stable than furanose
4. Open ring form is least common- aldehyde is unstable

Question 25

Describe what acetals are

Answer 25

1. Much harder to reverse than hemi-acetals 2. When both OH groups have R group attached 3. Require specific enzymes or stronger reagents (e.g. acids/bases) 4. In sugar acetals are called glycosides 5. The bond from C1 to the OR group is called the glycosidic bond 6. What formed when two sugars join

Question 26

How is an acetal formed

Answer 26

1. R-C=OH+ + 2HO-R' 2. 2 Eq of alcohol

Question 27

What is added to a saccharide to form a glycosidic bond

Answer 27

1. R'OH - can be another saccharide 2. H+ or enzyme

Question 28

Describe how disaccharide is formed

Answer 28

1. 2 saccharides can join together with OH of anomeric bond in one sugar and OH of another carbon on other sugar 2. 4 other reactive OH groups

Question 29

What are sugar acids

Answer 29

1. Gluconic acids- can't cyclise as no aldehyde 2. Glucuronic acid- has aldehyde and acid so can cyclise 3. Formed from oxidation of aldehyde or primary alcohol group

Question 30

What are sugar alcohols

Answer 30

1. Produced by reduction of aldoses or ketoses 2. Sorbitol is formed from glucose and mannitol from mannose 3. Contain no aldehyde so can't form rings

Question 31

What are alditols

Answer 31

1. A class of an acyclic polyol derived from an aldose by reduction of the carbonyl functional group

Question 32

What are 3 examples of alditols

Answer 32

1. Ribitol is a constituent of flavin co-enzyme 2. Glycerol and myo-inositol are components of lipids 3. Xylitol is a sweetner

Question 33

What are amino sugars

Answer 33

1. When one or more hydroxyl group of monosaccharides are replaced by amino groups the products are amino sugars 2. D-glucoasmine, D-galactasamine 3. The amino groups are sometimes acylated

Question 34

What is L-ascorbic acid

Answer 34

1. Vitamin C 2. A water soluble vitamin 3. Structure resembles monosaccharides

Question 35

What are deoxysugars

Answer 35

1. Sugars that contain one oxygen atom less than in the parent molecule 2. D-2-deoxyribose- part of DNA

Question 36

What are sugar phosphates

Answer 36

1. Phosphate derivatives of monosaccharides found in all living cells 2. Important intermediates in carbohydrate metabolism

Question 37

What are glycoproteins

Answer 37

1. Many proteins are functionalised by sugars post synthesis in the cell- glycosylation 2. Glycoproteins can be N-linked or O-linked 3. The rest of the sugar is then attached

Question 38

What is glycation

Answer 38

1. Uncontrolled addition of sugars to proteins 2. Important in Alzheimer's and diabetes

Question 39

Give a major example of glycoproteins

Answer 39

1. Erythropoietin hormone (EPO) 2. Secreted by kidneys 3. Stimulates production of red blood cells 4. Glycosylation increases stability and bioactivity 5. Can be used to treat anaemia

Question 40

What are 3 other examples of glycoproteins

Answer 40

1. Bacterial cell walls 2. Cartilage 3. Heparin

Question 41

Describe bacterial cell walls

Answer 41

1. Alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) with peptide cross-linkages

Question 42

Describe cartilage

Answer 42

1. Long, brush-like polysaccharides attached to central protein 2. Acts as a shock-absorber due to movement of water under pressure

Question 43

Describe heparin

Answer 43

1. Polysaccharide that helps prevent blood clotting