Intracellular Proteolysis

Question 1

Proteases are classed on their……..

Answer 1

Catalytic activity

Question 2

What are different types of proteases?

Answer 2

Serine protease
Cysteine protease
Aspartyl proteases=> endopeptidases, exopeptidases
Metalloprotease

Question 3

Give examples of digestive enzymes

Answer 3

Trypsin + chymotrypsin

Question 4

What is inactive form of chymotrypsin called?

How is it activated?

Answer 4

Chymotrypsinogen

Is activated by reaction of another enzyme trypsin that cleaves this form between amino acid 15 +16

Question 5

What is the inactive form of trypsin?

Answer 5

Trypsinogen

Question 6

What is an example of protein activation of proteolysis?

Answer 6

E.g. clotting factors

Question 7

What is an example of cysteine proteases?

What is its use?

Answer 7

Bromelain, Papain
Obtained from pineapple stems + papaya
Enzymes when they are added to meat digest collagen + extracellular which makes meat easier to chew

Question 8

What is an example of aspartyl protease?

What does it do?

Answer 8

HIV-1 protease (retropepsin)

Cleaves poly-protein precursors to form functional proteins

Question 9

What are the 3 enzymes involved in ubiquitylation?

Answer 9

E1= ubiquitin activating enzyme 
E2= ubiquitin conjugating enzyme 
E3= ubiquitin ligase

Question 10

What is ubiquitin?

Answer 10

Small peptide

Question 11

What is definition of half life?

Answer 11

Time it takes to degrade protein by half of what it was at the beginning
If protein doesn’t bind well, less likely ubiquited. Therefore long lived half life

Question 12

What is N end rule?

Answer 12

U3 ubiquitin ligase have poor affinity for stabilising amino-terminal residues

Question 13

SREBP cycle for cholesterol regulation

High cholesterol?

Answer 13

SREBP= Transcription factor so goes to nucleus and activates genes required for cholesterol supply
SCAP +SREBP form tight complex=> conformational changes so binds to Insig
Cholesterol levels are now high so SREBP remains in ER + doesn’t return to nucleus so can not activate transcription and target genes are switched off
Cholesterol binds to SCAP, leading conformational change to bind to Insig

Question 14

SREBP cycle

Low cholesterol?

Answer 14

SCAP + Insig dissociate as low cholesterol causes SCAP to lose its cholesterol=> conformational change is reversed + SCAP can no longer bind to Insig
Insig + SCAP go to Golgi apparatus
Protein activation by proteases activates SREBP. Active form is called N-SREBP
SREBP moves from Golgi apparatus to nucleus + activates gene for cholesterol biosynthesis + LDL receptor

Question 15

What are statins?

Answer 15

Are small molecules that block key enzyme in cholesterol biosynthesis pathway