Question

1. A mutation in the gene for DNA ligase will impact which strand during DNA replication a. The leading b. The laggingc. Both the leading and the lagging d. Neither the leading strand or the lagging strand

Answer 1

Answer 1 - C option is correct .

Explanation- Lagging strand is affected mostly , very very less leading strand is affected . This is because DNA ligase enzyme is most frequently used in lagging strand and less in leading strand.

In lagging strand ,their are many number of small fragments are present whichbis known as okazaki fragments.which always need to join ,which is done by DNA ligase enzyme .

Two missense mutation occuring in different alleles of DNA ligase I gene, encoding the major DNA ligase in proliferating mammalian cells which are detected in human fibroblasts strain. These cells exhibit retarded joining of okazaki fragments during DNA replication and hypersensitivity to a Verity of DNA damaging agent. 46BR ( fibroblasts strain) derived from a patient who displayed a symptom to immunodiffeciency and sun sensitivity. Strongly reduced ability of DNA Ligase I to form a labelled enzyme - adenylated intermediate correlated with the gene defect in 46 BR cells.

The data indicate that human DNA ligase is required for joining okazaki fragments during lagging strand DNA replication and the complications of DNA excision repair.

The 5' to 3' exonuclease activity of DNA polymerase I is needed to remove initial RNA primer of leading strand synthesis but it needs frequently to remove the primers of Lagging strand synthesis. DNA ligase is an enzyme that creates phosphodiester bonds between adjacent nucleotides between okazaki fragments.