What is the Difference Between Topoisomerase I and II

Topoisomerase I refers to the enzymes which cut one of the two strands of double-stranded DNA, relax the strand, and reanneal the strand while topoisomerase II refers to the enzymes which cut both strands of the DNA helix simultaneously in order to manage DNA tangles and supercoils.

1. What is the function of topoisomerase 1?
2. What is the function of topoisomerase II?
3. What do the enzymes topoisomerase I and topoisomerase II have in common?
4. How many types of topoisomerases are there?
5. What does Supercoiling mean?
6. What would happen if there was no topoisomerase?
7. What is negative supercoiling of DNA?
8. What enzyme prevents Supercoiling?
9. Why does type 2 topoisomerase require ATP?
10. Which topoisomerase makes a single stranded break?
11. What does gyrase do?

What is the function of topoisomerase 1?

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 is the function of topoisomerase II?

Type II topoisomerases change DNA topology by breaking and rejoining double-stranded DNA. These enzymes can introduce or remove supercoils and can separate two DNA duplexes that are intertwined (see Figure 12-16).

What do the enzymes topoisomerase I and topoisomerase II have in common?

What do the enzymes topoisomerase I and topoisomerase II have in common? They both have nuclease activity. They both create double-strand DNA breaks. ... They both can create winding (tension) in an initially relaxed DNA molecule.

How many types of topoisomerases are there?

Classes. DNA topoisomerases are divided into two classes: type I enzymes (EC; topoisomerases I, III and V) break single-strand DNA, and type II enzymes (EC; topoisomerases II, IV and VI) break double-strand DNA.

What does Supercoiling mean?

Supercoils refer to the DNA structure in which double-stranded circular DNA twists around each other. This is termed supercoiling, supertwisting or superhelicity -- meaning the coiling of a coil, also understood in terms of knots.

What would happen if there was no topoisomerase?

Topoisomerase alleviates supercoiling downstream of the origin of replication. In the absence of topoisomerase, supercoiling tension would increase to the point where DNA could fragment. DNA replication could not be initiated because there would be no RNA primer. DNA strands would not be ligated together.

What is negative supercoiling of DNA?

Negative supercoiling is the left-handed coiling of DNA thus winding occurs in the counterclockwise direction. It is also known as the "underwinding" of DNA. 2. ... Topoisomerases unwind helix to do DNA transcription and DNA replication.

What enzyme prevents Supercoiling?

DNA gyrase introduces supercoils, and DNA topoisomerase I prevents supercoiling from reaching unacceptably high levels.

Why does type 2 topoisomerase require ATP?

Type IIA topoisomerases are ATP-dependent enzymes that have been shown to simplify the topology of their DNA substrates to a level beyond that expected at equilibrium (i.e. more relaxed than the product of relaxation by ATP-independent enzymes, such as type I topoisomerases, or a lower than equilibrium level of ...

Which topoisomerase makes a single stranded break?

DNA Topoisomerase I introduces a single strand break into DNA, leaving the enzyme covalently attached to the 3′-end of the break by a phosphodiester bond to a tyrosine residue (Tyr723).

What does gyrase do?

DNA gyrase is an essential bacterial enzyme that catalyzes the ATP-dependent negative super-coiling of double-stranded closed-circular DNA. Gyrase belongs to a class of enzymes known as topoisomerases that are involved in the control of topological transitions of DNA.