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Y1 SEM 1: Medical Cell Biology and Genetics > S9) Protein Targeting and Collagen Biosynthesis > Flashcards

S9) Protein Targeting and Collagen Biosynthesis Flashcards

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1
Q

What is collagen?

A

Collagen is a secreted protein produced by fibroblasts in the connective tissue and is the most abundant protein in the body (25-35%)

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2
Q

Identify some structures composed largely of collagen

A
  • Tendons
  • Ligaments
  • Cartilage
  • Bone
  • Loose connective tissue
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3
Q

What is the basic unit of collagen?

A

Basic unit is tropocollagen

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4
Q

Describe the structure of the collagen molecule

A
  • Consists of 3 polypeptides
  • Rod-shaped protein
  • (Gly-X-Y)n repeat (glycine in every 3rd position in chain)
  • Characteristic triple helix (right-handed)
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5
Q

Which type of bonding in predominant in a collagen molecule?

A

H-bonds between α chains stabilise structure

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6
Q

State three structural benefits of the triple helix structure of collagen

A
  • Non-extensible
  • Non-compressible
  • High tensile strength
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7
Q

Why is glycine a central part of the collagen molecule?

A

Glycine is the only amino acid with a side chain small enough to fit in the middle of the helix

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8
Q

Which other monomers form an integral part of the collagen structure (Gly-X-Y)n ?

A
  • Proline
  • Hydroxyproline
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9
Q

What is prolyl hydroxylase and what does it do?

A

Prolyl hydroxylase is an enzyme which catalyses the formation of hydroxyproline and allows increased H-bonding to stabilise the collagen triple helix

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10
Q

What is scurvy?

A

- Scurvy is a condition which arises due to insufficient Vitamin C (ascorbic acid) intake

  • It presents with weakness, fatigue, and sore arms and legs
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11
Q

Why does scurvy occur?

A

Prolyl hydroxylase requires ascorbate as a cofactor to function so its absence compromises the enzyme’s function and and weak tropocollagen triple helices form

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12
Q

Describe the tissue distribution of Type I collagen

A

Type I collagen is found in the skin, tendons, ligaments and bone

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13
Q

Describe the tissue distribution of Type II collagen

A

Type II collagen is found in cartilage and intervertebral discs

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14
Q

Describe the tissue distribution of Type III collagen

A

Type III collagen is found in the foetal skin and cardiovascular system

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15
Q

Describe the tissue distribution of Type IV collagen

A

Type IV collagen is found in the basement membrane

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16
Q

Describe the tissue distribution of Type V collagen

A

Type V collagen is found in the placenta and skin

17
Q

The synthesis and modification of collagen involves three stages; synthesis in the ER, procollagen secretion and the formation of the collagen fibre.

In 7 steps, describe the synthesis and modification of collagen in the ER

A

⇒ Synthesis and entry of chain into lumen of rER

⇒ Cleavage of signal peptide (prepro α chains → pro α chains)

⇒ Hydroxylation of proline and lysine residues

⇒ N-linked glycosylation

⇒ Addition of galactose to hydroxylysine residues

⇒ Formation of disulphide bonds

⇒ Formation of triple-helical procollagen from C- to N-terminus

18
Q

The synthesis and modification of collagen involves three stages; synthesis in the ER, procollagen secretion and the formation of the collagen fibre.

In 4 steps, describe the secretion of procollagen from the cell

A

⇒ O-linked glycosylation (addition of glucose)

⇒ Transport vesicle

⇒ Exocytosis

⇒ Conversion of procollagen to tropocollagen (removal of N- and C-terminal propeptides)

19
Q

The synthesis and modification of collagen involves three stages; synthesis in the ER, procollagen secretion and the formation of the collagen fibre.

In 3 steps, describe the formation of the collagen fibre

A

⇒ Lateral association of collagen molecules

⇒ Covalent cross-linking

⇒ Aggregation of fibrils

20
Q

Summarise protein target signals to the ER in terms of:

  • Nature of signal
  • Signal location in the primary sequence
  • Folding during transfer
  • Specialist proteins involved
  • Signal retention/cleavage
  • Energy requirement
A
  • Nature of signal: Hydrophobic signal sequence
  • Signal location in the primary sequence: N-terminus
  • Folding during transfer: unfolded
  • Specialist proteins involved: SRP, SRP receptor & protein translocator
  • Signal retention/cleavage: cleaved by signal peptidase
  • Energy requirement: yes for hydrolysis of GTP
21
Q

Summarise protein target signals to the nucleus in terms of:

  • Nature of signal
  • Signal location in the primary sequence
  • Folding during transfer
  • Specialist proteins involved
  • Signal retention/cleavage
  • Energy requirement
A
  • Nature of signal: NLS (basic)
  • Signal location in the primary sequence: various positions on surface
  • Folding during transfer: folded
  • Specialist proteins involved: importin & RanGTP for transport and displacement of NLS
  • Signal retention/cleavage: retained
  • Energy requirement: yes for hydrolysis of GTP
22
Q

Summarise protein target signals to the mitochondria in terms of:

  • Nature of signal
  • Signal location in the primary sequence
  • Folding during transfer
  • Specialist proteins involved
  • Signal retention/cleavage
  • Energy requirement
A
  • Nature of signal: amphipathic signal
  • Signal location in the primary sequence: N-terminus
  • Folding during transfer: held partially unfolded by chaperones
  • Specialist proteins involved: Tom & Tim channel complex, chaperones
  • Signal retention/cleavage: cleaved
  • Energy requirement: yes, ATP hydrolysis by mHsp70
23
Q

Summarise protein target signals to the lysosomes in terms of:

  • Nature of signal
  • Signal location in the primary sequence
  • Folding during transfer
  • Specialist proteins involved
  • Signal retention/cleavage
  • Energy requirement
A
  • Nature of signal: Mannose-6-phosphate
  • Signal location in the primary sequence: signal patch for distinguishment
  • Folding during transfer: folded
  • Specialist proteins involved: M-6-P receptor in trans-Golgi
  • Signal retention/cleavage: phosphate cleaved by phosphatase
  • Energy requirement: Yes
24
Q

Summarise protein target signals for ER retention in terms of:

  • Nature of signal
  • Signal location in the primary sequence
  • Folding during transfer
  • Specialist proteins involved
  • Signal retention/cleavage
  • Energy requirement
A
  • Nature of signal: KDEL (Lys-Asp-Glu-Leu)
  • Signal location in the primary sequence: C-terminus
  • Folding during transfer: folded
  • Specialist proteins involved: KDEL Receptor
  • Signal retention/cleavage: retained
  • Energy requirement: only for formation of budding vesicle

Y1 SEM 1: Medical Cell Biology and Genetics (23 decks)

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