Question

Describe the process of supercoiling in prokaryote DNA.

IN your answer consider:

a. three forms of prokaryote circular DNA that may be observed

b. the key enzymes involved in supercoiling

Answer 1

As we know DNA of prokaryotic cell is also called as Genophore, which comprises of few million base pairs and lacks chromatin. The DNA of Prokaryote is compacted in the form of supercoiling that is either over-twisted or under-twisted DNA . It could be either 1: negatively supercoiled -In this process DNA is twisted in the opposite direction of the double helix or 2: Positively supercoiled - Here DNA twisting is in the same direction of the double helix. Normally, DNA is considered a B-form where 10-10.5 base pair per helical turn exists. When there is a strain developed in the helical axis the circular DNA either twist anti-clockwise or clockwise. The strains are produced by the enzymes topoisomerase by cutting phosphate backbone of DNA which changes the DNA topology. The circular DNA appears as eight-shaped lobe, negative or positive supercoiled forms. The supercoiling is important in gene expression.

a) Three forms of prokaryotic circular DNA are supercoiled, open-circular and linear.

b)The key enzymes are Topoisomerase I, III, IV, V and Reverse DNA gyrase.