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Fundamentals of the Living Cell > Intracellular proteolysis > Flashcards

Intracellular proteolysis Flashcards

Understand: - Mechanisms of proteolytic processes. - Mechanisms of action behind statins.

1
Q

Serine proteases [3 marks]

A
  • Have a very reactive serine residue in their active sites
  • Examples: thrombin, chymotrypsin
  • Serine residue has OH
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2
Q

Aspartyl proteases [2 marks]

A
  • Have a very reactive aspartate residue in their active sites
  • Example: HIV I protease
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3
Q

Bromelain and papain [2 marks]

A
  • Involved in meat tenderisers

- Digest collagen and other proteins to make meats easier to chew

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4
Q

Aspartyl proteases [2 marks]

A
  • Have a very reactive aspartate residue in their active sites
  • Example: HIV I protease
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5
Q

HIV I protease [3 marks]

A
  • Cleaves polypeortein precursors to Gag and Pol proteins
  • This helps makes new virions, which need to be processed for proteolysis
  • This enzyme is blocked by anti-retroviral drugs
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6
Q

What are gag proteins? [1 mark]

A
  • Group specific antigens
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7
Q

What are pol proteins? [1 mark]

A

Code for enzymes such as reverse transcriptase and HIV protease

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8
Q

Metalloproteases [2 marks]

A
  • Uses metal ions to catalyse proteolysis

- Two types; endopeptidase and exopeptidase

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9
Q

Endopeptidase [1 mark]

A

Cleaves off protein within sequence

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10
Q

Exopeptidase [2 mark]

A
  • Enzymes that cleave off single amino acid at the end

- Either from amino terminus or from the carboxyl terminus

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11
Q

Specific proteases [2 marks]

A
  • Recognises specific amino acid sequence

- Involved in protein activation (i.e. insulin)

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12
Q

Non-specific proteases [1 mark]

A

Involved in protein degradation (i.e. proteases in small intestine)

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13
Q

Synonyms for an inactive protein [2 marks]

A
  • Zymogen

- Proprotein

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14
Q

α-Chymotrypsin synthesis [3 marks]

A
  • Chymotrypsinogen is cleaved between position 6 and 7 to form π-Chymotrypsin
  • Autolysis of π-Chymotrypsin at position 13 and 16 and position 146 and 149 to form α-Chymotrypsin
  • Two depeptides are released from π-Chymotrypsin
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15
Q

Trypsin synthesis [2 marks]

A
  • Trypsinogen is cleaved off between position 6 and 7 to form trypsin
  • Enzyme used is enteropeptidase
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16
Q

What is needed for intron removal? [2 marks]

A
  • Specific sequences at splice donor and splice acceptor

- Needs an AG in front of the next exon

17
Q

Deficiency of factor IX (X linked haemophilia) cause and effect [4 marks]

A
  • Mutation creates a new splice acceptor
  • Exon starts with different nucleotide sequence
  • Reading frame shift creates a new amino acid sequence and abrupt stop codon
  • Blood cannot coagulate properly
18
Q

Ubiquitin [2 marks]

A
  • Covalently attached to proteins

- Guides protein to proteasome (26S proteasome)

19
Q

Ubiquitin activating enzyme 1 (E1) [2 marks]

A
  • Formation of thioester bond between C end of ubiquitin and cysteine in E1.
  • Requires ATP
20
Q

Ubiquitin activating enzyme 2 (E2) [1 mark]

A

Transfer of ubiquitin to a cysteine on E2

21
Q

Ubiquitin activating enzyme 3 (E3) [2 marks]

A
  • Transfer of ubiquitin from E2 to lysine on the target protein
  • Many different E3 exist that recognise specific target proteins
22
Q

Stabilising residue [2 marks]

A
  • U3 ubiquitin ligases have a low affinity to them

- Degradation of these proteins are slower

23
Q

Destabilising residue [2 marks]

A

U3 ubiquitin ligases have a high affinity to them

- Degradation is faster

24
Q

How do statins work? [3 marks]

A
  • Block cholesterol synthesis via inhibition of HMG CoA reductase
  • Acts like a competitive inhibitor
  • Increases uptake of LDL through LDL receptor
25
Q

What is the sterol regulatory element binding protein (SREBP)? [2 marks]

A
  • A transcription factor

- Regulates gene for enzymes

26
Q

SREBP action in low cholesterol [2 marks]

A
  • Binds to promotor of LDL receptor proteins

- Goes to nucleus and activates genes for cholesterol supply

27
Q

What happens in low cholesterol? [4 marks]

A
  • Insig and SCAP dissociate
  • Causes SCAP to reverse its conormational shape
  • In the Golgi, SREBP is activated via proteolysis to form N-SREBP (N terminus cleaved off)
  • N-SREBP released from the Golgi
28
Q

What is the purpose of N-SREBP? [1 mark]

A

Goes to the nucleus to activate cholesterol synthesis proteins

29
Q

What happens in high cholesterol? [4 marks]

A
  • SREBP is synthesised because proteins with transmembrane remains
  • It is anchored in the membrane of the endoplasmic reticulum and remains there.
  • Forms a complex with SCAP to cause a conformational change
  • This allows SCAP to bind to Insig.

Fundamentals of the Living Cell (35 decks)

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