Question

Which of the following statements about DNA polymerases I, II and III is TRUE?

-only DNA pol I can initiate DNA synthesis
-only DNA pol II can initiate DNA synthesis
-only DNA pol III can initiate DNA synthesis
-all three can initiate DNA synthesis
-none can initiate DNA synthesis

Answer 1

DNA polymerase III is the enzyme required for DNA synthesis, while DNA polymerase I and DNA polymerase II are primarily required for repair.

Step-by-step explanation:

In prokaryotes, DNA polymerase III (DNA pol III) is the enzyme required for DNA synthesis, while DNA polymerase I (DNA pol I) and DNA polymerase II (DNA pol II) are primarily required for repair.

Unlike DNA pol III, DNA pol I is a monomeric protein with 5'→3' exonuclease activity that removes RNA primers at the terminal end of DNA. DNA pol I also possesses polymerization and proofreading activity.

On the other hand, DNA pol II is an oligomeric protein that aids in DNA repair processes. Therefore, the statement 'only DNA pol III can initiate DNA synthesis' is true.

Answer 2

Only DNA polymerase III can initiate DNA synthesis during bacterial DNA replication, as it extends DNA strands from an RNA primer.

Step-by-step explanation:

Among the DNA polymerases I, II and III, the statement 'only DNA pol III can initiate DNA synthesis' is TRUE when referring to the role of these enzymes in bacterial DNA replication. DNA polymerase III is specifically responsible for synthesizing new DNA strands by adding nucleotides in the 5' to 3' direction, and it requires a primer with a free 3'-OH group – which is provided by RNA primase – to begin this process. Neither DNA polymerases I nor II can initiate DNA synthesis; however, DNA polymerase I is important for replacing the RNA primer with DNA and for its proofreading activity during DNA replication, while DNA polymerase II is involved in the DNA repair process.