In which enzyme would a defect majorly affect the formation of a whole new lagging strand without affecting the leading strand? A. DNA ligase B. helicase C. single-strand binding protein D. topoisomerase

The right answer is A. DNA ligase.

During replication, the "delayed" (or lagging) strand is synthesized discontinuously, in small fragments which are then sutured to each other. Their length is about 1500 to 2000 base pairs in Escherichia coli and 100 to 200 in eukaryotes). These segments have been called "fragments of Okazaki", named after their discoverers.

To start the DNA synthesis, the DNA polymerase requires an RNA primer that is synthesized by the RNA Primase, which is then extended into DNA.

In bacteria, DNA primase is an independent enzyme, whereas in eukaryotes it is associated within the DNA polymerase α / primase complex, where DNA polymerase α can extend the primer into DNA. The Okazaki fragment that results from this process is an RNA / DNA chimera, of which the RNA portion synthesized by the primase contains about ten ribonucleotides.

The RNA primer portion is finally degraded so that consecutive Okazaki fragments can be sutured. According to the organisms, this step is carried out either by a DNA polymerase having a 5 '→ 3' exonuclease activity (DNA polymerase I in bacteria), or by an RNAse H type activity which will remove the ribonucleosides and a flap nuclease (the FEN1) that will remove any excess deoxyribonucleotides, before a DNA polymerase fills the gap between the Okazaki fragments. The last step is suturing the fragments with a DNA ligase.

Without this ligase, the join between the Okazaki fragments will not happen, and this will affect the integrity of the DNA molecule.

Answer: The answer is A. DNA Ligase

Explanation: I did it on plato and got it correct.