![]() ![]() Thus, although backward chain is growing in the 3 ‘→ 5’ direction, in fact Okazaki Fragments are being synthesized in the 3 ‘← 5’ direction.Īfter the primers are removed, nucleic acid gaps between Okazaki Fragments are filled and a final enzyme, DNA ligase, binds fragments to form a single, single strand of continuous DNA. The fragments resulting from this discontinuous replication are called ‘Okazaki Fragments’. In this process, several small fragments of the delayed chain are replicated as replication fork advances (5 ‘→ 3’) and further separates the double helix from DNA molecule. To work around this problem, cell makes copies the strand that is oriented 3 ‘← 5’ in a discontinuous manner. The problem lies in the other strand, which is oriented in 3 ‘← 5’ direction, in which DNA polymerase cannot bind and perform its function because the opening of replication fork occurs in the opposite direction to replication. For this reason, this chain is called ‘leader chain’. Since the two strands of DNA molecule are antiparallel and replication fork separates the two strands at the same site, strand in the 5 ‘→ 3’ direction is easily replicated towards the opening of replication fork. Termination of replication is triggered by (a) DNA polymerase (b) Helicase (c) SSB (d) Tus protein. View Available Hint (s) ResetHelp Parental DNA DNA ligase Lagging strand 0 Leading. During replication, Okazaki fragments elongate (a) leading strand towards the replication fork (b) lagging strand towards the replication fork. However, a major hindrance to DNA replication comes from the fact that DNA polymerase enzyme can only perform its function of nucleic acid polymerization (addition of nucleic acids to the growing strand) in 5 ‘→ 3’ sense. Explain why Okazaki fragments are formed. At the end of replication there are two DNA molecules, each of the double strand containing one strand originating from cell and one copied (hence the name semi-conservative replication). Then another enzyme, DNA polymerase, recognizes the primers added by RNA polymerase and starts copying the DNA strands. An RNA polymerase is the constituent of this complex that adds small primers to the beginning of DNA single strand to be copied. Separation of DNA single strands leads to formation of replication fork, where the replication machinery (protein and enzyme complex) will bind. DNA ligase is responsible for joining Okazaki fragments on the lagging strand during replication. This process is based on semi-conservative copy of DNA in the nucleus of a growing cell.ĭNA replication then begins with distortion of double helix by topoisomerase, followed by separation of two DNA strands by helicase. Primase adds an RNA primer to help initiate DNA replication. Okazaki Fragments refers to small single stranded DNA fragments, formed upon DNA replication, more specifically, the back strand.įor normal cell growth and division in organisms, an initial step called DNA replication is required. Finally, DNA ligase 1 seals the resulting nick by forming a phosphodiester bond between adjacent DNA nucleotides.
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