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Question Marathons Explained

Let's start off with an easy question:

What are the three main polymerases involved in bacterial DNA replication? What are the functions of each one?

DNA polymerase I, DNA polymerase III, and Primase are the major polymerases involved in bacterial DNA replication.

Primase is an RNA polymerase that creates primers made of ribonucleotides on both the lagging and leading strands. These primers provide the necessary 3'-OH group for DNA polymerase to add nucleotides.

DNA Pol III uses these RNA primers as a starting point for the synthesis of the leading strand and the Okazaki fragments on the lagging strand. DNA polymerases cannot initiate de novo polynucleotide synthesis, but rather extend in the 5' to 3' direction by adding dNTPs to the 3'-OH group of a primer or a pre-existing DNA strand.

DNA Pol I assumes several key roles in DNA replication. One of these is to remove the RNA primers from the synthesized strands, a process facilitated by its 5' to 3' exonuclease activity. DNA Pol I also plays a significant role in synthesizing DNA on the lagging strand to replace the RNA primers immediately following their removal. In addition, DNA pol I aids in proofreading DNA during replication; it can remove mispaired bases with its 3' to 5' exonuclease activity, then replace them with a correct base using it polymerase activity.

DNA Pol II is another important bacterial polymerase but does not have a major function in DNA replication. Like DNA Pol I, DNA pol II can also perform proofreading and editing during replication, though it is not involved in primer removal and replacement. DNA pol II has especially low processivity compared to other polymerases because it lacks a beta clamp motif. Since the processivity of polymerase is the number of bases incorporated in one binding event, low processivity means that DNA pol II frequently falls off the DNA strand and then binds again to another region of DNA. This quality of DNA pol II allows it to disassociate from the DNA strand and reassociate downstream of a lesion or gap, effectively acting as a bypass polymerase during replication when the replication fork is stalled. Meanwhile, these short gaps or lesions block the activity of DNA pol III because it has high processivity and stays bound to the DNA even though it cannot continue strand extension. This process is known as translesion DNA synthesis and is an important mechanism of replication-coupled DNA repair.

I should have specified DNA polymerases, but you are correct!

Thanks for confirming! Next question:

Define each of the following terms describing stages of the life cycle of Plasmodium falciparum. Also, state whether each stage occurs in the sporogonic, exoerythrocytic, and/or erythrocytic portions of the Plasmodium life cycle:
1. Schizont
2. Trophozoite
3. Sporozoite
4. Gametocyte
5. Ookinete
6. Merozoite