Protein Sorting // Translocation 2

Question 1

Why does protein degradation occur?

Answer 1

It is a major regulatory strategy of the cell.

Question 2

What are the 3 functions of protein degradation?

Answer 2

1) Store nutrients in the form of proteins and break them down in times of metabolic need.
2) Eliminate abnormal proteins.
3) Permit regulation of cellular metabolism (Eliminate superfluous enzymes and regulatory proteins.)

Question 3

How many hydrolytic enzymes are in lysosomes?

Answer 3

There are 50 hydrolytic enzymes.

Question 4

What are the main functions of lysosomes?

Answer 4

1) Degrade substances which the cell takes up via endocytosis.
2) Recycle intracellular constituents which are enclosed within vesicles which fuse with lysosomes.

Question 5

How is a secondary lysosome formed?

Answer 5

Phagosome fuses with primary lysosome from the Golgi apparatus and thus, creates a secondary lysosome.

Question 6

What happens to the residual undigested contents in phagocytosis?

Answer 6

Exocytosis occurs and so these undigested contents are released from the cell.

Question 7

Which processes are associated with lysosomal activity?

Answer 7

1) Muscle Wastage caused by disuse or denervation.

2) Regression of the uterus after childbirth.

Question 8

How are proteins marked for degradation?

Answer 8

Covalent linkage with ubiquitin allows proteins to be marked for degradation. ( The ubiquitin is the marker which allows degradation to happen. )

Question 9

Which sub - units have proteolytic activity?

Answer 9

Beta sub - units.

Question 10

Why does proteolytic activity occur inside the proteasome?

Answer 10

Prevents unspecific destruction of cytosolic proteins.

Question 11

Name some biological processes which are ubiquitin dependent?

Answer 11

Cell - cycle progression // organ formation // circadian rhythms // tumour supression // antigen processing.

Question 12

What are some of the different functions that ubiquitin chains have?

Answer 12

Signalling // trafficking // cell cycle regulation // DNA repair // degradation

Question 13

Explain the ubiquitin conjugation pathway.

Answer 13

1) Carboxyl end of ubiquitin is linked to E1 enzyme via thioester bond. (Requires ATP.)
2) Activated ubiquitin is transferred to cysteine residue of E2.
3) Transfers ubiquitin from E2 to target protein.