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BB10004 > Carbohydrate polymers and glycoproteins > Flashcards

Carbohydrate polymers and glycoproteins Flashcards

1
Q

What is the general empirical formula for a polysaccharide

A
  1. (CH2O)n ± N, P, S
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2
Q

What are the 3 class sizes of carbohydrates

A
  1. Monosaccharides
  2. Oligosaccharides
  3. Polysaccharides
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3
Q

What are the main features of monosaccharides

A
  1. Stereoisomers
  2. 3, 4, 5 and 6 carbon sugars
  3. Ring formation
  4. Ring isomers
  5. Boat and Chair conformations
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4
Q

What are the main features of dissacharides

A
  1. Sugars can be attached to each other by O-glycosidic bonds
  2. The simplest of these are the disaccharides in which two sugars are attached to each other
  3. Alpha- OH below the ring
  4. Beta- OH above the ring
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5
Q

Name 3 important disaccharides and what they are composed of and whether they are reducing or non-reducing

A
  1. Maltose- alpha-glucose-(1–>4)-glucose (reducing)
  2. Lactose – ß-galactosyl-(1–>4)-glucose (Reducing)
  3. Sucrose – α-glucosyl-(1–>2)-fructose (non-reducing)
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6
Q

What is an oligosaccharide

A
  1. 2 – 8 linked monosaccharides (so disaccharides are included)
  2. Relatively low natural abundance of 3 – 8 saccharide molecules (and most of these are in plants)
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7
Q

What are the main features of a polysaccharide

A
  1. > 8 saccharide units
  2. Divided into two main groups:
  3. Structural
  4. Storage
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8
Q

Give two examples of structural polysaccharides

A
  1. cellulose

2. Chitin

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9
Q

Describe the basic structure of cellulose

A
  1. homopolymer of glucose units which are β(1–>4) linked

2. unbranched

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10
Q

Describe the basic structure of chitin

A
  1. homopolymer of N-acetylglucosamine β(1–>4) linked, 2. unbranched
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11
Q

Why do cellulose and chitin have beta 1–>4 linkages

A
  1. Beta 1–>4 linkage forms straight chains

2. Interactions between hydroxyl group and oxygen, a long, linear straight chain forms- strong

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12
Q

Give 2 examples of storage polysaccharides

A
  1. Starch

2. Glycogen

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13
Q

Describe the structure of starch

A
  1. A mixture of two polymers:
  2. α-amylose – unbranched glucose polymer linked by α(1–>4)
  3. amylopectin - α(–>6) linked with branches every 24-30 glucose
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14
Q

Describe the structure of glycogen

A
  1. Very similar to amylopectin but even more branched- every 8-14 residues
  2. Predominantly alpha 1-4 links with alpha 1-6 links every 8-14 residues
  3. Alpha 1-4 linkages cause coiled chains
  4. Coiled structure more compact so good storage
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15
Q

What are Glycosaminoglycans (mucopolysaccharides) (GAG)

A
  1. A range of polymers composed of repeating disaccharide units
  2. Typically several 100s of units long
  3. The major components of ground substance
  4. The stuff between cells in animals
  5. Forms a molecular glue that holds cells together
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16
Q

Give an example of a glycosaminoglycan (GAG)

A
  1. Hyaluronic acid
17
Q

Describe the structure of hyaluronic acid

A
  1. Found in ground substance, synovial fluid and vitreous humour of the eye
  2. Disaccharide of D-glucuronic acid β(1–>3) linked to N-acetyl-D-glucosamine
  3. Disaccharide units are attached to each other with β(1–>4) linkages
  4. 250 to 25 000 disaccharide units
  5. Forms a rigid and highly hydrated structure as every other linkage is beta 1-4
  6. Viscous solution, absorbs shocks and shearing forces
18
Q

What are glycoproteins

A
  1. The majority of proteins are post-translationally modified by the addition of carbohydrates – to form glycoproteins
  2. Carbohydrate structure generated without strict genetic control
  3. Availability of the enzymes determines the exact nature of the carbohydrates – which results in microheterogeneity
  4. Carbohydrate content can vary from <1% to >90% of the weight of the glycoprotein
19
Q

What is microheterogeneity

A
  1. Variation in the chemical structure of a substance that does not produce a major change in its properties.
20
Q

How are carbohydrates attached to proteins to form glycoproteins

A
  1. Carbohydrate attached in two ways:
  2. N-linked- nitrogen on side chain of the amino acid
  3. O-linked- oxygen on side chain of the amino acid
21
Q

Describe the N-linkage in glycoproteins

A
  1. N-acetylglucosamine (NAG) β linked to the amide nitrogen of Asn in the protein sequence Asn-X-Ser or Asn-X-Thr, where X is any amino acid except Pro
  2. Recognises these sequences as N-linkage site
  3. Further sugars are added to this base
22
Q

Describe the O-linkage in glycoproteins

A
  1. Attachment is to the OH group of either Ser or Thr
  2. Even more variable than N-linked
  3. Range from a single galactose to 1000 disaccharide units

BB10004 (14 decks)

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