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Yr 1 - Proteins & Enzymes > Collagen > Flashcards

Collagen Flashcards

1
Q

What is collagen?

A

Family of fibrous proteins that form insoluble fibres

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2
Q

What property makes them appropriate for bone, tendon, cartilage etc

A

High tensile strength

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3
Q

Structure?

A

Consists of 3 polypeptide chains. These vary between collagen types

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4
Q

1ary structure

A

Every 3rd residue is Gly. Repeating sequence is Gly-X-Y. X is usually Pro (Gly-Pro-Y) and Y is usually Lys (Gly-X-Lys)

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5
Q

Why is every 3rd residue Gly?

A
  • Every 3rd residue of each polypeptide passes through centre of triple helix
  • Gly is the amino acid with the smallest side chain so is only one that can fit in centre
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6
Q

What happens when Gly residue is replaced with an amino acid with a larger side chain during a mutation?

A

Helix can no longer wind so tightly, leads to ineffective collagen

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7
Q

2ary structure

A

Each polypeptide chain forms a left-handed helix with 3.3 residues per turn (collagen helix)

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8
Q

What is normal amount of residues per turn?

A

3.6

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9
Q

3ary structure

A
  • 3 polypeptide chains lie parallel and twist round each other
  • This forms triple helix (right handed)
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10
Q

What is name of triple helix?

A

Procollagen (before removal of extension peptides)

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11
Q

Where is collagen finally secreted into?

A

Extracellular spaces of connective tissue

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12
Q

When do post-translational modifications occur?

A

Occurs before polypeptide chains form helix

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13
Q

Which residues are hydroxylated?

A

Proline and Lysine

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14
Q

What are the products of this hydroxylation?

A

Hydroxyproline (Hyp) and Hydroxylysine (Hyl)

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15
Q

What enzymes are involved in hydroxylation?

A

Prolyl hydroxylase and lysyl hydroxylase

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16
Q

What is required as co-factor?

A

Vitamin C

17
Q

What causes scurvy?

A

Vitamin C deficiency; Hyp and Hyl and not synthesised. Results in weakening of collagen fibres

18
Q

Symptoms of scurvy

A

Skin lesions, fragile blood vessels, poor wound healing

19
Q

What is name of structure after post-translational modifications?

A

Procollagen (triple helix)

20
Q

What are extension peptides?

A

Collagen chains are synthesised with additional amino acid chains at each end (N & C termini)

21
Q

What forms between C-terminal extensions of neighbouring polypeptide chains?

A

Disulphide bonds

22
Q

What enables these bonds to form?

A

Extensions often contain Cys

23
Q

What is purpose of these bonds?

A
  1. Facilitates triple helix assembly

2. Help prevent premature aggregation

24
Q

When are extension peptides removed?

A

Removed after secretion into extracellular space.

25
Q

How are extension peptides removed?

A

Removed by peptidase enzymes

26
Q

How are fibrils formed?

A

After extension peptides are removed, tropocollagen aggregate and form fibrils

27
Q

What are fibrils stabilised by?

A

Covalent cross-links

28
Q

Where do covalent cross-links act?

A

Between and within tropocollagen molecules (hold chains together)

29
Q

Why are these covalent cross-links not disulphide bonds as commonly found in proteins?

A

Lack of Cys in final mature collagen

30
Q

What is Osteogenesis Imperfecta?

A

Brittle bone disease; inherited. Increased risk of bone fracture

31
Q

What causes OI?

A

Spontaneous mutation in Type I collagen chains

32
Q

What enzymes break down collagen?

A

Collagenase enzymes

33
Q

How do tumour cells utilise collagenase enzymes?

A

They often secrete collagenase enzymes to help them destroy the connective tissue surrounding tumours (help in tumour invasion and metastasis)

34
Q

When does procollagen become tropocollagen?

A

Once extension peptides are removed (after secretion)

35
Q

What is Ehlers-Danlos Syndrome?

A

Collagen deficiency (deficiency in lsysl oxidase) so cross-links aren’t formed properly (weak)

Symptoms: hypermobile joints, hyperextensibility of skin, extreme fatigue

36
Q

What is Dupuytren’s Contracture?

A

Caused by excess collagen production affecting connective tissue of hand, causing tendons in hand to contract and little finger and ring finger curve over

37
Q

What has recently be used to treat Dupuytren’s Contracture?

A

Injection of collegenase to break down excess collagen

Yr 1 - Proteins & Enzymes (8 decks)

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