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FLC > Intracellular Proteolysis > Flashcards

Intracellular Proteolysis Flashcards

1
Q

Define proteolysis

A

Break down of proteins by proteases

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2
Q

What is the role of statins?

A

Statins block cholesterol synthesis by inhibiting HMG-CoA reductase

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3
Q

Which enzymes are responsible for proteolysis?

A
  • peptidases
  • proteinases
  • proteases
  • cathepsins
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4
Q

What does the N end rule state?

A

The N end terminal amino acids (after methionine cleaved off by methionine peptidases) determine a proteins half life

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5
Q

Name the enzymes involved in protein ubiquitylation

A

E1 - Ubiquitin activating enzyme
E2 - Ubiquitin conjugating enzyme
E3 - Ubiquitin ligase

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6
Q

What is the consequence of statins inhibiting cholesterol biosynthesis?

A

Leads to the upregulation of LDL receptors
LDL removed from bloodstream - less cholesterol in blood
- so cells take up cholesterol from blood
- upregulating gene transcription

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7
Q

How is ubiquitin attached to the substrate protein?

A

Covalently polymerased to the protein

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8
Q

How does the liver use cholesterol?

A

Liver converts cholesterol into bile acids which are secreted throughout the bile ducts

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9
Q

What is the function of metalloproteases?

A

Cleave off metal proteins

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10
Q

Explain what is meant by the N end rule?

A

Rule governing rate of protein degradation by recognising the residue of proteins at the N end terminal

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11
Q

What do endopeptidases do?

A

Cleave amino acids off the middle of polypeptide chains

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12
Q

Which TF activates the genes required for the cholesterol biosynthesis pathway?

A

SREBP

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13
Q

What is a proteosome?

A

Large protein complex

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14
Q

Explain what happens when there is high cholesterol levels?

A
  1. SREBP + SCAP = tight complex
  2. SREBP remains in ER
    - doesn’t go to nucleus - transcription not activated
  3. INSIG anchors complex to ER
  4. Cholesterol binds to SCAP (allosteric protein)
  5. SCAP(with cholesterol) binds to INSIG
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15
Q

How are proteins categorised based on their half lives?

A
  1. short lived

2. long lived

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16
Q

Why does SREBP form complex with SCAP?

A

By binding to SCAP, SREBP can be transported to the golgi in vesicles

17
Q

Name examples of exopeptidases

A

Aminopeptidases

Carboxypeptidases

18
Q

Outline the process of protein ubiquitylation using enzymes

A
  1. COOH on ubiquitin forms a thioester bond with E1 Cysteine using ATP
  2. Ubiquitin molecule transferred to the target protein
    from E2 to E3
  3. E3 enzymes are specific to target proteins
19
Q

Give an example of non specific proteolysis?

A

Ubiquitin Protease Pathway - significant for protein degradation

20
Q

Explain how the Cholesterol biosynthesis pathway deals with low cholesterol?

A
  1. SCAP + INSIG dissociate
    - low cholesterol reverses the conformational changes
    occured (no longer complementary)
  2. SCAP and INSIG move to Golgi via vesicular transport
  3. Proteases activate SREBP via proteolysis
  4. Activated SREBP leaves golgi
  5. In Nucleus activates genes for cholesterol biosynthesis
    and LDL receptors
21
Q

What is the role of exopeptidases?

A

Cleaves off amino acids at the end of polypeptide chains

22
Q

What is SREBP?

A

Sterol regulated element binding proteins

Membrane bound transcription factors synthesised on the ER membranes

23
Q

How does non specific proteolysis occur?

A

Compartmentalised as acidic proteases present in lysosomes

24
Q

What is the benefit of protein ubiquitylation?

A

Marks the protein for degradation via the proteosome

25
Q

What causes X linked Haemophillia?

A

Deficiencies of Factor VIII or IX in clotting cascade pathway
mutated gene found on X chromosome
Haemophilia B caused by single nucleotide base change in clotting Factor IX gene
- incorrect RNA splicing
- non functional, truncated protein formed

26
Q

What is a half life?

A

The time it takes to degrade half the amount of protein at the start of the measurement

27
Q

Where are cysteine proteases found?

A

In fruits - pineapple, papaya, fig and kiwi

28
Q

Which proteins require specific proteolysis in order to be activated?

A
  1. Digestive enzymes

2. Clotting factors

29
Q

What are the uses of cysteine proteases?

A

Meat tenderiser

- digests collagen and extracellular matrix

30
Q

What is specific proteolysis?

A

When proteolytic enzyme recognises a specific base sequence to activate a protein
- a protein needs cleaving to be activated from a proprotein

31
Q

What is the function of HIV-1 protease?

A

HIV-1 Protease is essential to the life cycle of HIV

32
Q

What is non specific proteolysis

A

The degradation of proteins

33
Q

What is a significant aspartyl protease?

A

HIV- 1 protease

34
Q

How does HIV-1 cause infection?

A
  1. HIV protein generates 2 proteins GAG and POL
  2. These are processed by proteolysis
  3. HIV-1 proteolysis cleaves proproteins GAG and POL -> activated
  4. Able to infect cells
35
Q

Explain how digestive enzymes undergo specific proteolysis

A
  1. Chymotrypsinogen (precursor of chymotrypsin) activated by trypsin enzyme
  2. Trypsin cleaves the precursor at Arg15+16 to activate it
  3. Chymotrypsin undergoes autolysis
    - cleaves itself at Ser14 - Arg15 and Thr147-Asn148
  4. Produces 3 chains connected by disulphide bonds
36
Q

Give an example of clotting factors

A

Serine proteases

37
Q

Where are digestive enzymes produced?

A

Generated by exocrine pancreas

Secreted to small intestine

38
Q

How are clotting factors activated via specific proteolysis?

A

In a cascade pathway
one activated (cleaved enzyme) activates the next
e.g. E9 activated by the activation of E12

FLC (34 decks)

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