Correct option is D
Let’s evaluate each statement about the reversibility of post-translational modifications in cells:
A. Ubiquitination of proteins is reversible, but ADP-ribosylation of DNA is irreversible.
Ubiquitination is indeed reversible; deubiquitinating enzymes (DUBs) can remove ubiquitin from proteins. However, ADP-ribosylation of DNA is generally reversible, as enzymes like PARG (poly-ADP-ribose glycohydrolase) can remove ADP-ribose groups. So, this statement is incorrect.
B. Ubiquitination of proteins is reversible, but myristoylation of proteins is irreversible.
Ubiquitination is reversible, as mentioned. Myristoylation, a lipid modification involving the addition of a myristoyl group to a protein, is typically irreversible because there are no known enzymes to remove it. This statement is correct.
C. Ubiquitination of proteins is irreversible, but ADP-ribosylation of DNA is reversible.
Ubiquitination is reversible, not irreversible, so this statement is incorrect.
D. Both ADP-ribosylation of DNA and prenylation of proteins are reversible.
ADP-ribosylation of DNA is reversible, as noted. Prenylation (addition of isoprenoid groups like farnesyl or geranylgeranyl) is generally considered irreversible because there are no specific enzymes to remove these groups. This statement is incorrect.
E. Both prenylation and myristoylation of proteins are irreversible.
Both prenylation and myristoylation are irreversible modifications, as there are no known enzymes to remove these lipid groups. This statement is correct.
Correct answer is 4 : B and E
