Question

In DNA replication ywhat are the leading and lagging strand synthesis plus the activities of DNA helicase, DNA gyrase, DNA polymerase, RNA primase and

DNA ligase

Answer 1

DNA replication: It is a biological process through which DNA makes its copy during cell division in all living organisms. First of all uncoiling of double stranded DNA takes place after that the separated strand single strand of DNA used as a template for semi-conservative synthesis of two new double stranded DNA. The synthesis of one strand takes place in 5’ - 3’ direction known reverse of DNA fork known as the leading strand. It serves as a template for continuous DNA synthesis. However, the second strand the synthesis takes place from 5’-3’ in the direction of DNA fork known as lagging strand. It serves as a template for the discontinuous strand synthesis. There are several molecules involved in this process as

DNA helicase: It is an enzyme help in an unwinding of DNA double strands, forming a bubble like structure known as replication fork. In this process the breaking of hydrogen bonds between the nucleotides of double strand takes place. Genes of human genome encode approx 95 non-redundent helicases. Out of which 31 are DNA helicases and 64 are RNA helicases.

DNA gyrase (Type II topoisomerase enzyme): This enzyme help in reliving the reliving of strain while the DNA double strand is unwounded. This enzyme also induces the negative supercoiling of DNA relaxing the positive supercoiling.

DNA polymerase: This is an enzyme used for the synthesis of new nucleotide strand. It is essential for DNA replication usually works in pairs to create two identical double stranded DNA strand from the original single stranded DNA strand. DNA polymerase basically DNA dependent DNA polymerase (Induce extension of DNA strand through 3’ end) and RNA dependent DNA polymerase (Reverse transcriptase catalyzes RNA templet directed extension of the 3’end of DNA strand).

RNA primase: It is an enzyme used in the synthesis of short RNA primer elongated by DNA pull one nucleotide at a time.

DNA ligase: It is an enzyme facilitate in joining of DNA strand together by catalyzing the formation of phosphodiester bonds. It plays a role in repairing single-strand breaks in duplex DNA in living organisms