Question

4. Plastocyanin mRNA is translated on 80S ribosomes. How many membranes
must the plastocyanin polypeptide pass through (by translocation) in order to
reach the thylakoid lumen where it is active?
a. 1
b. 3
c. 4
5. Which of these proteins serves as an inhibitor of apoptosis and is encoded by
a proto-oncogene?
a. p53
b. Rb
c. Bcl2

Answer 1

4. Option b is correct .

As the polypeptide is synthesised on the cytoplasmic ribosomes and then it is transported to the thylakoid lumen. Thylakoid are present inside chloroplast and have their own membrane.

So polypeptide needs to pass through 2 membranes of chloroplast and 1 membrane of thylakoid to enter into thylakoid lumen. In total, 3 membranes.

5. Option c is correct.

p53 and Rb are the tumor suppressor genes encoded proteins. They supports apoptosis. When they get mutated , they loose their function.

Bcl2 is encoded by protooncogene and it inhibits cell apoptosis.