The concentration of a particular protein X in a normal human cell rises gradual

Question

The concentration of a particular protein X in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X protein do not decrease. Which of the following mutations could explain these results?

a. A mutation that results in the loss of an enzyme that adds a ubiquitin tag to the protein.

b. a mutation in gene X that results in the loss of polyA addition to its mRNA

c. a mutation in gene X that changes the sequence that encodes sites at which ubiquitin can be attached to the protein

d. Both A and C

A previous answerer said the answer is c. Is this true? Please explain.

Explanation / Answer

Both A and C

Ubiquitinization is a process to degrade protein and if any mutation is their that effect the binding of ubiquitin then the ubiquitnazation will not occur and the protein concentration will remain high that will prevent cell division. same is true for option A also if their is any mutation in the enzyme like ubiquitin-activating enzymes that leads to ubiqitization will also give same kind of results.

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