Difference Between Helicase and Topoisomerase

The main difference between helicase and topoisomerase is that helicase unwinds the double-stranded DNA whereas topoisomerase relieves the tension created by helicase. Furthermore, helicase breaks the hydrogen bonds between the two DNA strands while topoisomerase breaks the phosphodiester linkages in the DNA backbone.

1. What are the major differences between helicases topoisomerases and ligases used in DNA replication?
2. What comes first topoisomerase or helicase?
3. How are the functions of helicase and topoisomerase related?
4. What is the function of topoisomerase?
5. Why do Okazaki fragments form?
6. Who discovered Okazaki fragments?
7. What does a helicase do?
8. Why does DNA synthesis occur in the 5 '- 3 direction?
9. What are the 4 steps of replication?
10. What does topoisomerase mean?
11. What is Primase made of?
12. Why does DNA polymerase need a primer?

What are the major differences between helicases topoisomerases and ligases used in DNA replication?

The major difference between helicases, topoisomerases and ligases is that helicases and topoisomerases unwind DNA, with topoisomerases functioning to relieve supercoil stress ahead and behind the replication fork. Finally, ligase is sealed DNA that has been broken or synthesized via okazaki fragments.

What comes first topoisomerase or helicase?

Helicase opens up the DNA at the replication fork. Single-strand binding proteins coat the DNA around the replication fork to prevent rewinding of the DNA. Topoisomerase works at the region ahead of the replication fork to prevent supercoiling.

How are the functions of helicase and topoisomerase related?

The helicase actively separates the two parental DNA strands while the topoisomerase, working in front of the helicase, allows relaxation of positive supercoils in a highly processive manner.

What is the function of topoisomerase?

Topoisomerase I is a ubiquitous enzyme whose function in vivo is to relieve the torsional strain in DNA, specifically to remove positive supercoils generated in front of the replication fork and to relieve negative supercoils occurring downstream of RNA polymerase during transcription.

Why do Okazaki fragments form?

Okazaki fragments form because the lagging strand that is being formed have to be formed in segments of 100–200 nucleotides. This is done DNA polymerase making small RNA primers along the lagging strand which are produced much more slowly than the process of DNA synthesis on the leading strand.

Who discovered Okazaki fragments?

They were discovered in the 1960s by the Japanese molecular biologists Reiji and Tsuneko Okazaki, along with the help of some of their colleagues.

What does a helicase do?

Helicases are enzymes that bind and may even remodel nucleic acid or nucleic acid protein complexes. There are DNA and RNA helicases. DNA helicases are essential during DNA replication because they separate double-stranded DNA into single strands allowing each strand to be copied.

Why does DNA synthesis occur in the 5 '- 3 direction?

DNA is always synthesized in the 5'-to-3' direction, meaning that nucleotides are added only to the 3' end of the growing strand. As shown in Figure 2, the 5'-phosphate group of the new nucleotide binds to the 3'-OH group of the last nucleotide of the growing strand.

What are the 4 steps of replication?

• Step 1: Replication Fork Formation. Before DNA can be replicated, the double stranded molecule must be “unzipped” into two single strands. ...
• Step 2: Primer Binding. The leading strand is the simplest to replicate. ...
• Step 3: Elongation. ...
• Step 4: Termination.

What does topoisomerase mean?

: any of a class of enzymes that reduce supercoiling in DNA by breaking and rejoining one or both strands of the DNA molecule.

What is Primase made of?

Archaeal and eukaryote primases are heterodimeric proteins with one large regulatory (human PRIM2, p58) and one small catalytic subunit (human PRIM1, p48/p49). The large subunit contains a N-terminal 4Fe–4S cluster, split out in some archaea as PriX/PriCT.

Why does DNA polymerase need a primer?

The synthesis of a primer is necessary because the enzymes that synthesize DNA, which are called DNA polymerases, can only attach new DNA nucleotides to an existing strand of nucleotides. ... The primer therefore serves to prime and lay a foundation for DNA synthesis.