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Biochemistry > Structural Proteins > Flashcards

Structural Proteins Flashcards

1
Q

List the intracellular structural protein(s)

A

Keratin

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2
Q

List the extracellular structural protein(s)

A
  • Collagen
  • Elastin
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3
Q

Keratin

A
  • Structural protein
  • Found in skin, hair, nails hoofs and feathers
  • High stability from cysteine disulphide bonds
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4
Q

Alpha-keratin

A
  • Consist of alpha helices
  • Forms b-keratin at high temp
  • Stabilised by disulphide bonds
  • Hair, wool, nail, hoof
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5
Q

Beta-keratin

A
  • Stronger than alpha-keratin
  • Beta-pleated sheet
  • Feathers and reptile scales
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6
Q

Disulphide bonds in keratin can be reduced by…

A

Thioglycol

or another reducing agent

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7
Q

Composition of wool

A
  • 3 alpha keratin macromolecules → 1 Protofibril
  • 11 protofibrils → 1 Microfibril
  • Microfibril → Macrofibril
  • Macrofibril → Wool fibre
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8
Q

What stabilises the polypeptide chain of keratin?

A

Disulphide bonds

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9
Q

Cells on the outer layer of the epidermis

A
  • Dead cells
  • Held together by a network of keratin fibres
    • Provided by keratinocytes
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10
Q

Synthesis of keratin

A
  1. Pre-keratin produced in cells
  2. Skin cells mature and become keratinized
  3. Cells of the stratum basale go upwards
  4. Keratin-containing stratum corneum formed
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11
Q

Keratin can be degraded by…

A
  • Thioglycolates
  • Keratinase (moth larvas)
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12
Q

List the extracellular matrix components

A
  • Collagen
  • Elastin
  • Fibronectin
  • Laminin
  • Proteoglycans
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13
Q

Collagen (extracellular)

A
  • Very abundant fibrous protein
  • Insoluble in water
  • Skin, bone tendon, cartilage blood vessels
  • Not found in plants
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14
Q

Structure of collagen

A
  • Basic unit: Tropocollagen (triple helix structure)
  • Striated
  • Gly & Pro / hydroxyPro / hydroxyLys are prominant in the peptide chains
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15
Q

How does a lack of vitamin C cause scurvey?

A
  • Vitamin C needed for collagen synthesis
  • Bleeding gums, loosening teeth
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16
Q
  • Process name
  • Enzyme required
A
  • Hydroxylation of Lysine
  • Lysine hydroxylase (Requires vitamin-C)
17
Q
A
18
Q

End product name

A

5-OH-Lys (Hyl)

19
Q

End product name

A

4-OH-Pro (Hyp)

20
Q
  • Process name
  • Enzyme required
A
  • Hydroxylation of Proline
  • Proline hydroxylase (requires vitamin C)
21
Q

Due to the high level of Pro / hydroxyl-Pro, the polypeptide chains of collagen cannot…

A
  • Form alpha-helix/B-sheet
  • Left-handed helix conformation instead
  • This conformation allows the 3 helices to interlock (tropocollagen)
22
Q

Structural units of collagen

A

Tropocollagens → microfibrils → macrofibrils → fibres

23
Q

What binds tropocollagen units?

A
  • Cross links (C=C/C=N bonds)
  • Disulphide bonds
  • H-Bonds
24
Q

What is the purpose of Pro/Lys being converted to hydroxy-Pro/hydroxy-Lys?

A
  • Pro/Lys cannot hydrogen bond
  • Converted to hydroxy- in order to form hydrogen bonds
25
Q

Lys-aldehyde + Lys-aldehyde →

(Allysine + Allysine →)

A

Condensation: Cross linkage

26
Q

Give the varieties of collagen in order of abundance

A
  • Collagen-I
  • Collagen-II-IV
  • Collagen-V-VII
27
Q

Every third amino acid in collagen is…

A

Glycine

(Forms a helix)

28
Q

What structural change does hydroxy-Lysine undergo during collagen synthesis?

A

hydroxy-Lysine is glycosylated (Gal-Gal-Glu)

Chains twist together and form a triple helix (procollagen)

29
Q

Describe the stages of collagen synthesis

A
  1. Transcription + Translation
  2. Pro → OH-Pro, Lys → OH-Lys
  3. OH-Lys glycosylated → procollagen
  4. C and N-terminus propeptides removed
  5. Tropocollagen
  6. Cross linkage → Type I collagen
30
Q

Which enzyme removes the C- and N-terminus propeptides?

A

Procollagen peptidase enzyme

31
Q

What can degrade collagen?

A
  • Collagenase enzyme
    • Microbial collagenase
      • Clostridium
    • Tissue collagenase
      • Tadpole tail resorption
      • Wound healing
32
Q

Elastin

A
  • Protein in connective tissue
  • Important in arteries, lung, skin, bladder
  • Elastic and expansible
  • Primarily composed of Gly, Pro (Lys)
33
Q

Describe the structure of elastin

A
  • Linking of soluble tropoelastin molecules
  • Cross-linked by H-bonds and covalent bonds
  • Insoluble, durable crosslinked array formed
34
Q

Synthesis of elastin

A

Begins in the cytoplasm of fibrocytes

  1. Tropoelastin formation
  2. Extracellular crossling formation
  3. Elastin fibre production
35
Q

Degradation of elastin

A
  1. Tropoelastin
  2. Mature elastin + Elastase enzyme →
  3. Elastin fragments
36
Q

Where is elastase formed and stored?

A
  • Pancreas
  • Leucocytes, stored in granulocytes

Biochemistry (21 decks)

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