A double helix DNA structure can be coiled or even supercoiled. In order to relieve the tension that is inevitably formed by this coiling, topoisomerase acts upon the DNA to relieve the stress that has been created. Helicase unwinds DNA before replication. DNA polymerase elongates the DNA during replication. RNA polymerase makes RNA from a template strand of DNA. Primase creates a temporary primer to begin DNA synthesis/replication.

In DNA replication, the role of helicase is to unwind the strand by breaking the hydrogen bonds that hold that two strands together.

All of the other answer choices describe a role performed by a different DNA replication enzyme. Let's go ahead and review these.

• Lays down an RNA primer so that the synthesis of complementary daughter DNA can occur

This enzyme is called Primase.

• Stitches together the various daughter DNA fragments into a single strand

This enzyme is called DNA Ligase. It is able to join the okazaki fragments formed on the lagging strand, as well as any other areas where there is a break in the strand.

• Holds the parent DNA strands in place during replication to prevent them from associating with one another

This enzyme is known as single-strand binding protein.

DNA polymerase I is in prokaryotes only. It degrades the RNA primer and fills in the gap with DNA. DNA polymerase III has  synthesis and proofreads with  exonuclease. This is also in prokaryotes only. It elongates the leading strand by adding deoxynucleotides to the 3’ end. It elongates the lagging strand until it reaches primer of preceding fragment.  exonuclease activity “proofreads” each added nucleotide. The function of DNA polymerase II is unknown.

Remember, it’s complementary and antiparallel. Therefore, when writing the complement of the DNA sequence, it’s 3’ to 5’, so you must change answer to be 5’ to 3’. 

Ribonucleotide reductase regulates the rate of DNA synthesis and the total  DNA to cell mass ratio. The enzyme converts adenosine diphosphate (ADP), guanosine diphosphate (GDP), cytidine diphosphate (CDP), uridine diphosphate (UDP). The ribonucleotide thymidine diphosphate is not a substrate for this enzyme. Thymidine nucleotides are products of another enzyme: thymidylate kinase.

Purines can be synthesized de novo from ribose phosphate. 5-phosphoribosylamine is converted to inosine monophosphate, which is an intermediary for adenine monophosphate and guanine monophosphate production. The reaction requires the presence of glycine, aspartate and glutamine, but not lysine.

Phosphoribosyl pyrophosphate (PRPP) is a precursor of both purines (adenine and guanine), as well as pyrimidines (cytosine, uracil, and thymine) in nucleotide synthesis. In certain enzyme deficiencies, levels of PRPP can increase leading indirectly to uric acid production and gout.

Nucleases are important in excision of  nucleotides from the DNA chain. Phosphodiester bonds between two nucleotides are broken and the DNA chain becomes fragmented. Site-specific nucleases can function as restriction enzymes cutting phosphodiester bonds at specific locations inside the DNA molecule. In DNA repair they remove nucleotides incorrectly placed during DNA synthesis.

DnaA protein in bacteria binds to a base pair sequence at the origin of replication serving as an initiation factor for DNA synthesis. All the other answers are wrong as: helicase, not DnaA protein unwinds DNA; single-stranded DNA binding protein stabilizes separated DNA strands; primase synthesizes RNA primers; and DNA polymerase I replaces RNA with DNA.

Because the lagging strand is created in various separate segments during DNA replication, after polymerization they must be joined together by an enzyme. The enzyme that is responsible for these connections is DNA ligase.