Question

Using your knowledge of the proteins involved in the process of DNA replication, and their requirements for activity, please add to or re-draw each of the following DNA diagrams as would be needed to account for the effect of adding only DNA pol I and dNTPs to each DNA molecule. Please briefly explain the rationale for each diagram. (Note: Each circular or linear line represents a single strand of DNA or RNA. See legend below)

Question 3: (6 marks) Using your knowledge of the proteins involved in the process of DNA replication, and their requirements for activity, please add to or re-draw each of the following DNA diagrams as would be needed to account for the effect of adding only DNA poll and dNTPs to each DNA molecule. Please briefly explain the rationale for each diagram. (Note: Each circular or linear line represents a single strand of DNA or RNA. See legend below) Legend RNA DNA 5' 3' (b) 5' 4 3' (c) 5' 002 3" 5' 3' 5 5'3'

Answer 1

Case A: DNA Pol 1 will extend the primer from the 3' end using the template (blue solid line in diagram) to synthesize the new strand. After it reaches the 3' end of the template no further extension can take place as the bases are missing in the template itself. Also ligase is absent to repair the nick in the template to continue with the process of replication.

Case B: DNA pol I will start the process of replication from both the primers. As the template is circular, two possible outcomes can happen. i) Replication starts from primer 1 (P1) and synthesize the new strand due to the polymerase activity and in the process replace the second primer and its product owingto the 3' to 5' exonuclease activity. The new strand (shown in black) is formed with a small nick remaining at the 3' end where the primer p1 was present. ii) Replication starts from primer set 2(P2) similar to P1 and in the process synthesize the new starnd replacing the product of P1 due to exonuclease activity. The new starnd will conatin a small nick where the 3' end of P2 was present.

The nicks cannot be joined due to the absence of ligase.

Case C: Synthesis will start from both the primers but the second primer (P2) is always downstream of the first primer (P1). Thus the DNA Pol I that starts from P1 will start extending using the template and in the process remove the product of P2 due to its exonuclease activity. generating the new strand represented in black in the attached diagram

Please follow the attached diagram for reference.

P PRIMER 1 TEMPLATE DNA POLI NEW STRAND INTP 3/ A PRIMER I (P) DNA PoiI → TEMPLATE dNTP > NEW STRAND LA PRIMER 2 (P2) NEW STRAND PRIMERI (PI) A PRIMER 2 (P2) NEWSTRAND © I, s 3 ' 3! 31 Y TEMPLATE