Explain the roles of specific enzymes in prokaryote DNA replication. [7 marks]

DNA replication is the same in eukaryotes and prokaryotes; the question just emphasizes that the process depends on enzymes and their functions need to be explained.DNA gyrase (or topoisomerase II) relieves the strains on the double helix, facilitating uncoiling of DNA. Helicase unwinds the DNA double helix by breaking the hydrogen bonds between the linked base pairs in the two strands. DNA primase adds a small RNA sequence at the 5' end of the strand that is being replicated to initiate the activity of DNA polymerase (III). DNA polymerase III recognizes the RNA primer and adds the complementary (deoxyribo)nucleotides in a 5'-3' direction, thus synthesizing the complementary DNA strand. DNA polymerase I is responsible for removing the short RNA primer sequence needed for replication initiation. DNA polymerases III and I both proofread the DNA newly-formed strand by taking part in the previously described processes. Since in the lagging strand the DNA replication happens in fragments (the Okazaki fragments), DNA ligase is an enzyme that will link these small sections of replicated DNA (or otherwise ligase seals the nicks).

Answered by Hristo S. Biology tutor


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