What is the 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 helicase and topoisomerase?
2. What comes first topoisomerase or helicase?
3. What are the major differences between helicases topoisomerases and ligases used in DNA replication?
4. What is the function of topoisomerase?
5. What does a helicase do?
6. Is topoisomerase an helicase?
7. Why do Okazaki fragments form?
8. Why does DNA synthesis occur in the 5 '- 3 direction?
9. Why are Okazaki fragments necessary?
10. Who discovered Okazaki fragments?
11. What are the 4 steps of replication?
12. What is the order of enzymes in DNA replication?

What are helicase and topoisomerase?

Helicase breaks the hydrogen bonds between strands of DNA, unwinding the double helix. The unwinding action causes the strand to become more tightly wound further up from the fork. Topoisomerase periodically breaks the peptide backbone of one strand to relieve some of that tension created by helicases.

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.

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 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.

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.

Is topoisomerase an helicase?

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.

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.

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.

Why are Okazaki fragments necessary?

Therefore, efficient processing of Okazaki fragments is vital for DNA replication and cell proliferation. During this process, primase-synthesized RNA/DNA primers are removed, and Okazaki fragments are joined into an intact lagging strand DNA.

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 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 is the order of enzymes in DNA replication?

Primase (lays down RNA primers) DNA polymerase III (main DNA synthesis enzyme) DNA polymerase I (replaces RNA primers with DNA) Ligase (fills in the gaps)