Question

What would happen in each of the following cases? Assume in each case that the protein involved is a soluble protein, not a membrane protein.

1. You add a signal sequence (for the ER) to the N-terminal end of a normally cytosolic protein.
2. You change the hydrophobic amino acids in an ER signal sequence into charged amino acids.
3. You change the hydrophobic amino acids in an ER signal sequence into other hydrophobic amino acids.
4. You move the N-terminal ER signal sequence to the C-terminal end of the protein.

Answer 1

Answer:

A):

• The cytosolic protein would be targeted to the ER.

B):

• Changing hydrophobic amino acid to charge amino acid would derecognise it as an ER signal therfore it may not enter the ER.

C):.

• The hydrophobic core is important of recognination therfore changing to other hydrophobic amino acids would derecognise it as an ER signal.
• Therfore it may not enter the ER.

D):

• On moving the signal to C terminal end the protein would be relased from the ribosome without enetering the lumen of ER

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