Question

Question 1 (1 point)

Saved

Imagine that you are working with DNA sequences of soluble proteins (not membrane proteins) and have the technology to genetically engineer/alter the existing sequence and you can express this particular protein in a yeast cell model.

You also have the power to track and visualize where the genetically engineered proteins traffic in your model system.  

You engineer an ER signal sequence to the amino-terminal end of a normally cytosolic protein.   

Which best describes the fate of this protein?

Question 1 options:

	A. The protein is translocated through the ER membrane translocon channel, N’ end first
	B. The protein is translocated through the ER membrane translocon channel, C’ end first
	C. The protein remains in the cytosol

Question 2 (1 point)

You engineer an ER signal sequence to the carboxyl-terminal end of a normally cytosolic protein.   

Which best describes the fate of this protein?

Question 2 options:

	A. The protein is translocated through the ER membrane transloconchannel, N’ end first
	B. The protein is translocated through the ER membrane transloconchannel, C’ end first
	C. The protein remains in the cytosol

Answer 1

1) proteins with N terminal signal sequence will be translated to the ER lumen.

the ribosome in the cytosol start to translate the mRNA once the signal sequence is produced ( in the cytosol protein is synthesized from N terminal to C terminal) SRP, Signal recognition particle binds to the signal sequence then SRP binds to the SRP receptor on the rough endoplasmic reticulum, then loads the signal sequence, mRNA-ribosome complex to the translocon and then the ribosome translates the protein into the ER lumen, so the answer is

A) The protein is translocated through the ER membrane translocon channel, N’ end first

2) the C terminal signal sequence is translated at last, because translation occurs from N terminus to C terminus, the signal sequence will be loaded to the translocon by the SRP so the answer is B) The protein is translocated through the ER membrane translocon channel, C’ end first