Protein sorting and trafficking 7

Question 1

What type of polypeptide sequence targets the ER?

Answer 1

• Hydrophobic stretch of aminos acids , situated at the n terminus of the protein
• They usually have a positively charged N - terminus and a then a cleavage sequence

Question 2

What is the Signal Recognition particle (SRP) made up of?

Answer 2

• when a signal sequence emerges from the ribosome , it is recognised by a ribonucleoprotein complex - which makes up the SRP

Question 3

What happens when the SRP binds to the ribosome?

Answer 3

halts protein translation

Question 4

What happens when the SRP has bound to the ribosome?

Answer 4

attach to the SRP receptor in the ER membrane , This protein is called a translocon

Question 5

What does GTP hydrolysis do to the SRP and the SRP receptor?

Answer 5

GTP hydrolysis changes the conformation of the SRP and SRP receptor. The SRP is released from the ribosome .

Question 6

What happens once the SRP is released?

Answer 6

Ribosome translation resumes . Extension of the polypeptide chain push sthe chain through the ER membrane into the lumen

Question 7

What is the role of signal peptidase?

Answer 7

cleaves the polypeptide chain as it is passing through the protein translocator. Release a mature soluble protein in the ER lumen and creates a new N-terminus of the protein

Question 8

What are non-cleavable signal sequences signal-anchor sequences?

Answer 8

They tend to have a longer hydrophobic stretches of amino acids and no signal peptidase cleavage sequence

Question 9

Where do protein start their synthesis , which are targeted to the ER?

Answer 9

Proteins targeted to the ER start their synthesis in the cytosol

Question 10

How are proteins targeted to the ER?

Answer 10

signal sequence that allows ribosome-nascent chain-complex to be recognised by SRP

Question 11

What are the first two steps of protein formation?

Answer 11

• RER then to the Golgi

Question 12

What are the 4 steps of vesicle formation?

Answer 12

1) Vesicle buds from donor compartment
2) Vesicle pinches off and translocates
from donor to acceptor compartment
3) Vesicle docks with acceptor compartment
4) Vesicle fuses with acceptor compartment releasing contents into lumen

Question 13

What are needed for the formation of vesicles?

Answer 13

protein coats

Question 14

What is the name of a well known protein coat on vesicles?

Answer 14

Clathrin coats

Question 15

What molecule is the clatharin coats made up of?

Answer 15

Triskelion structure

Question 16

What protein cleaves vesicles containing clatharin coats?

Answer 16

• dynamin

Question 17

What pathways are associated with Cathrin coats ?

Answer 17

• Golgi to the late endoderm

- Cell exterior to the early endosome

Question 18

What are other types of protein coats?

Answer 18

• COP1

- COP2