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aa Biomolecules > Lecture 4 - Carbohydrates > Flashcards

Lecture 4 - Carbohydrates Flashcards

1
Q

What are saccharides

A
  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
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2
Q

What are the functions of saccharides

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

What are glycoconjugates

A
  1. General classification for carbohydrates covalently linked with other chemical species
  2. Glycoconjugates are formed via glycosylation
  3. Modify solubility, stability and life span
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4
Q

What are 4 examples of glycoconjugates

A
  1. Glycoproteins
  2. Proteoglycans
  3. Glycolipids
  4. Oligosaccharides
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5
Q

What are the 4 classes of saccharide

A
  1. Monosaccharide
  2. Oligosaccharide
  3. Polysaccharide
  4. Monosaccharide derivatives
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6
Q

What is a monosaccharide

A
  1. Sugars which cannot be hydrolysed to give a simple sugar
  2. e.g. Fructose
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7
Q

What is an oligosaccharide

A
  1. A carbohydrate which is composed of a small number of monosaccharide units (2-3)
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8
Q

What is a polysaccharide

A
  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
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9
Q

What are examples of monosaccharide derivatives

A
  1. sugar acids
  2. Sugar alcohols
  3. Alditols
  4. Amino sugars
  5. Deoxysugars
  6. L-ascorbic acid
  7. Sugar phosphates
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10
Q

What is an aldose

A
  1. A monosaccharide which contains an aldehyde
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11
Q

What is a ketose

A
  1. A monosaccharide which contains a ketone
  2. Can also use the suffix -ulose instead of -ose
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12
Q

What is the simplest unit of a sugar

A
  1. Glyceraldehyde
  2. Not sugar itself- what they are built up from
  3. Contains chiral carbon
    4.
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13
Q

How do you draw Fischer projections

A
  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
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14
Q

What is an anomeric position

A
  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.
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15
Q

What form do sugars naturally exist

A
  1. Aldoess and ketoses (reducing sugars) can cyclise
  2. Pentoses (furanose) and hexoses (pyranose) particularly favoured
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16
Q

What is the Haworth representation

A
  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
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17
Q

What is the Mills representation

A
  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
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18
Q

What is chair representations

A
  1. Chair like configuration
    2.
19
Q

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

A
  1. All OH groups are equatorial
  2. Anomeric position OH is pointing up and equatorial
  3. Pyran ring- 6 membered
  4. Beta-D-glucopyranose
20
Q

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

A
  1. OH in anomeric position is axial pointing down
  2. Alpha-D-glucopyranose
  3. Alpha OH always pointing down
21
Q

What happens to the 5 position OH

A
  1. CH2OH is opposite to side to what the 5OH would have been
22
Q

How is the hemiacetal formed

A
  1. Reversible reaction with water
  2. R-C=O (R-C=OH+)reacts with HO-R
  3. Aldehyde is protonated -
23
Q

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

A
  1. Beta-pyranose- most common
  2. Alpha-pyranose
  3. Beta-furanose
  4. Alpha-furanose
  5. open ring
24
Q

Describe order of frequency of the forms of glucose

A
  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
25
Q

Describe what acetals are

A
  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
26
Q

How is an acetal formed

A
  1. R-C=OH+ + 2HO-R’
  2. 2 Eq of alcohol
27
Q

What is added to a saccharide to form a glycosidic bond

A
  1. R’OH - can be another saccharide
  2. H+ or enzyme
28
Q

Describe how disaccharide is formed

A
  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
29
Q

What are sugar acids

A
  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
30
Q

What are sugar alcohols

A
  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
31
Q

What are alditols

A
  1. A class of an acyclic polyol derived from an aldose by reduction of the carbonyl functional group
32
Q

What are 3 examples of alditols

A
  1. Ribitol is a constituent of flavin co-enzyme
  2. Glycerol and myo-inositol are components of lipids
  3. Xylitol is a sweetner
33
Q

What are amino sugars

A
  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
34
Q

What is L-ascorbic acid

A
  1. Vitamin C
  2. A water soluble vitamin
  3. Structure resembles monosaccharides
35
Q

What are deoxysugars

A
  1. Sugars that contain one oxygen atom less than in the parent molecule
  2. D-2-deoxyribose- part of DNA
36
Q

What are sugar phosphates

A
  1. Phosphate derivatives of monosaccharides found in all living cells
  2. Important intermediates in carbohydrate metabolism
37
Q

What are glycoproteins

A
  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
38
Q

What is glycation

A
  1. Uncontrolled addition of sugars to proteins
  2. Important in Alzheimer’s and diabetes
39
Q

Give a major example of glycoproteins

A
  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
40
Q

What are 3 other examples of glycoproteins

A
  1. Bacterial cell walls
  2. Cartilage
  3. Heparin
41
Q

Describe bacterial cell walls

A
  1. Alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) with peptide cross-linkages
42
Q

Describe cartilage

A
  1. Long, brush-like polysaccharides attached to central protein
  2. Acts as a shock-absorber due to movement of water under pressure
43
Q

Describe heparin

A
  1. Polysaccharide that helps prevent blood clotting

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