The ER and Co-Translational Pathway

Question 1

What are the main components of the endomembrane system?

Answer 1

The ER and Golgi Apparatus

Question 2

What is the RER responsible for?

Answer 2

Synthesis, folding, modification, and transport of proteins destined for other endomembrane organelles

Question 3

Why is it called the co-translational pathway?

Answer 3

Because while the mRNA is being translated on the ribosome, it is also being transported through the ER simultaneously

Question 4

What is the SRP and what does it do?

Answer 4

The signal recognition particle ensures that the rest of the protein synthesis takes place on the RER

Question 5

What happens to the signal sequence once in the lumen of the RER?

Answer 5

It is cleaved away from the rest of the molecule

Question 6

What did Gunter Blöbel win a Nobel Prize for?

Answer 6

For the discovery that proteins have intrinsic signals that govern their transport and localisation in the cell

Question 7

What are two types of luminal proteins

Answer 7

Enzymes that are destined for the lysosome, and secreted proteins or peptides (eg prolactin)

Question 8

What are three types of integral membrane proteins?

Answer 8

Receptor molecules on the plasma membrane (eg insulin receptor)
Channel proteins (eg Sec proteins that make up the translocon in ER)
Adhesion molecules (eg ICAM - 1)

Question 9

How is quality controlled in the ER?

Answer 9

Chaperonins prevent premature folding as protein enters RER
Chaperonins bind to irreversibly folded proteins and retain them in the ER
Proteolytic enzymes in the ER can degrade misfiled proteins or they can be transported out of the ER

Question 10

What are the functions of the SER?

Answer 10

Synthesis of lipids
Detoxification of lipid soluble substances
Metabolism of carbohydrates
Storing pools of calcium ions (for cell signalling)
The addition of receptors to cell membrane proteins

Question 11

What kind of cells are rich in SER area?

Answer 11

Steroid hormone secreting cells, liver cells, myocytes