Question

1) What are double-strand breaks, and how does homologous recombination repair them?

2) What types of genes are transcribed by RNA polymerase I, II, III? Be sure that it is clear which genes are for which polymerase.

Please only answer in sentences no pictures, etc.

Answer 1

1) Double strand breaks are the damage that occurs to the double stranded DNA helices. The ionizing or the ultraviolet radiations actually are responsible for such damages. These radiations attack both the strands of the DNA and thus there is damage and breaking of the DNA double helix.
Homologous recombination repair is a DNA repair mechanism that is accomplished using a correct or undamaged DNA strand for repairing the damaged DNA. Homologous recombination repair uses RAD51 as the detector of the break point and RAD5 binds to the area. Then there is strand invasion and homologous repairing of the damaged DNA by a new set of proper strands creating Holliday junction. DNA synthesis occurs after strand invasion and then there is second end capture and then dissolution and ligation by the DNA ligase.

2)

RNA polymerase types	Genes transcribed
RNA polymerase I	transcribes genes encoding precursor rRNA (pre-rRNA), which is processed into 28S, 5.8S, and 18S rRNAs.
RNA polymerase II	protein-coding genes; miRNAs
RNA polymerase III	transcribes genes encoding tRNAs, 5S rRNA, and an array of small, stable RNAs, including one involved in RNA splicing (U6) and the RNA component of the signal-recognition particle (SRP)