Double-strand breaks cause genomic instability and are thus potentially lethal to cells. They also greatly increase the risk of cancer and the chance of chromosome structural mutations. Compare and contrast the two mechanisms of double-strand break repair. Why would one mechanism be used over another

Explanation:

All organisms suffer by double-strand breaks (DSBs) in their DNA.

DSBs  caused by  exposure to exogenous agents such as radiations, also by certain chemicals, and through endogenous processes, including DNA replication and repair.

Double-strand break repair:

The processing and repair of DSBs can lead to mutations, they can also lead to loss of heterozygosity, and chromosome rearrangements that can result into cell death or cancer.

DNA double-strand breaks are repaired by two main pathways( routes):  

i) Non-homologous end joining and  

ii) homologous recombination .

Homologous recombination- it takes place by means of replication, using the homologous strand as template. Homologous recombination therefore requires extensive regions of DNA homology in another DNA duplex, and  there is no loss of genetic information normally.

Non-homologous end joining- It requires no homology with a second DNA duplex and no, or only a few base pairs of, homology between the two broken DNA ends.

Homologous recombination is the mainly preferred mechanism in yeast.

Non-homologous DNA end joining is more commonly mutagenic than  homologous recombination  repair.

Explanation:

Double strand break leads to genomic rearrangements and instability,two mechanisms of double-strand break repair are:

Homologous recombination:occurs between two DNA molecules and completed in following sequential steps:

Non homologous end joining(NHEJ):

Homologous recombination is considered a more accurate mechanism for double strand repair because broken ends use homologous sequences elsewhere in the genome (sister chromatids, homologous chromosomes, or repeated regions on the same or different chromosomes) to prime repair synthesis

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!