Which enzyme is most directly responsible for the main process of producing a new DNA strand?
DNA polymerase II
DNA polymerase IV
DNA polymerase III
DNA polymerase I
The correct answer and explanation is:
The correct answer is DNA polymerase III.
DNA polymerase III is the enzyme most directly responsible for the main process of producing a new DNA strand during DNA replication. This enzyme is the primary polymerase involved in the elongation of the new DNA strand. DNA polymerase III synthesizes the new DNA strand by adding nucleotides to the growing chain in a 5′ to 3′ direction. It does so using the single-stranded DNA as a template, which is unwound by helicase during the replication process.
DNA polymerase III also has high processivity, meaning it can add many nucleotides before dissociating from the template strand. This characteristic makes it the main enzyme for continuous strand synthesis during DNA replication. Additionally, DNA polymerase III has a proofreading function. It has 3′ to 5′ exonuclease activity, allowing it to correct errors by removing incorrect nucleotides immediately after they are added.
Other DNA polymerases play important roles during replication but in different ways. DNA polymerase I is responsible for removing RNA primers used in the initiation of replication and replacing them with DNA. DNA polymerase II and DNA polymerase IV have roles in DNA repair processes and are not directly involved in the elongation of the DNA strand during replication. DNA polymerase II is mainly involved in repairing DNA damage that occurs between rounds of replication, while DNA polymerase IV is involved in translesion synthesis, allowing replication to continue past certain types of DNA damage.
Thus, while other polymerases assist in replication and repair, DNA polymerase III is the enzyme directly responsible for the primary task of synthesizing the new DNA strand.