Question

1. What are 3 similarities and 3 differences between HR and NHEJ?

Answer 1

Double stranded DNA break is a dangerous DNA lesion.If left unpaired it results in loss of genetic information,chromosomal abbrations or even death may occur.The major pathways for the repair of Double Stranded DNA break(DSB) is by homologopus recombination HR and non homologous end joining,NHEJ .

The similarities between HR and NHEJ is -both repairs pathways and play important role in mammalian DSB repair.

HR and NHEJ balance is essential for the genome stability .

HR and NHEJ is strongly influenced by chromosomal location

Difference is - homologous recombination leads to accurate repair and NHEJ is intrinsic mutagenic and HR is restricted to the S and G2 phase of cell cycle due to the requirement for the sister chromatid as a template. and NHEJ is active throught out the cell cycle and doesnot rely on a template.

NHEJ of compatible ends are fast process which completes approximately in 30 minutes and HR is much slower and take hours upto 7 hrs to complete the process.

NHEJ modifies the broken DNA ends and ligates them together with no regard of hmology or insertions.While HR uses an undamaged DNA template to repair the break,and it leads to the reconstitution of original sequence.