Protein Targeting

Question 1

Protein synthesis occurring at the ER?

Answer 1

1) signal sequence synthesised at N-termini
2) Signal recognised by SRP and binds to a receptor on the ER membrane
3) Ribosome now bound to the ER membrane
4) New protein guided through the translocation tunnel in ER lumen
5) Signal sequence then cleaved via signal peptidase and then recycled

Question 2

Proteins after their synthesis in the ER?

Answer 2

When proteins leave the ER they’re folded, then move to the Cis-face of the Golgi, then from the trans face they leave in vesicles which bud off from the Golgi

Question 3

How proteins transport from ER to the golgi?

Answer 3

1) proteins synthesised, folded and modified in the ER
2) Cis-golgi form vesicles and Trans golgi mature proteins for vesicles
3) Vesicles transport proteins from cytoskeleton pathways

Question 4

Purpose of the golgi?

Answer 4

The golgi allows for the formation of integral membrane proteins, secretory pathways and allow formation of lysosomes

Question 5

How are vesicles targeted to specific compartments?

Answer 5

Vesicle snares are complementary to plasma membrane snares so they can bind

Question 6

How are proteins targeted from ribosomes?

Answer 6

1) Ribosomes form proteins
2) folded proteins become cytoplasmic proteins and are transported into the peroxisome of the nucleus
3) unfolded proteins are put into the mitochondria

Question 7

How are proteins targeted to the mitochondria?

Answer 7

1) protein is complexed with a chaperone which takes it to the mitochondria
2) A signal sequence binds to a receptor and allows for diffusion of protein into a matrix where the signal sequence is cleaved and protein is folded
* This happens before proteins are folded

Question 8

How are proteins targeted to the nucleus?

Answer 8

• This happens after proteins are folded
  1) nuclear proteins contain nuclear localisation signal which binds to importin and goes through the nuclear pore
  2) it requires G-protein and hydrolysis of GTP

Question 9

How are proteins targeted to the lysosomes?

Answer 9

1) Lysosomal proteins are tagged with mannose 6 phosphate in golgi.
2) The M6 receptor in golgi directs proteins into transport vesicles which become a lysosome

Question 10

What is protein targeting disorder?

Answer 10

This is where proteins dont reach the lysosomes and enzymes are secreted instead. It stops lysosomes functioning properly, slows growth, developmental defects known as L-cell disease