INTRODUCTION Double stranded breaks (DSB) occur frequently in eukaryotic cells. It can be caused by

1800 WordsApr 23, 20198 Pages
INTRODUCTION Double stranded breaks (DSB) occur frequently in eukaryotic cells. It can be caused by many factors such as ultra violet radiation, reactive oxygen species, ionizing radiation et cetera (Lieber,2010). DNA damage leads to rapid growth of tumor leading to cancer. Hence it is very important to repair it before the cell undergoes further division. Two mechanisms of repair system can occur in the cell – homologous recombination (HR) and non homologous DNA end joining (NHEJ). These repair systems along with their mechanism and the repair factors associated with it has been analyzed in this paper. In order for repair factors to access the DNA that are packaged, chromatin remodelers are essential to open the DNA. One way of DNA being…show more content…
Thus many cells stall the division process at the first checkpoint. This is known as G1 arrest. Various DNA repair factors are recruited to the site of double stranded break in order to repair it. However, DNA is tightly packaged into complex chromatin structure and the chromatin is further packaged into 30 nm fibers preventing access to various enzymes and repair factors (Annunziato,2008). As cited in Avvakumov’s paper, wrapping of DNA around the nucleosome is one way in which DNA packs itself into a closed structure . Nucleosomes are present in eukaryotes but not in prokaryotes (Annunziato, 2008). It consists of four core histone pairs – H2A, H2B, H3 and H4. Each histone has a three helix domain called histone fold along with two unstructured tails. H2A-H2B and H3-H4 heterodimers are formed by histone-histone interaction which further associate to form octamers (Rhodes,1997). Positively charged histones interact with negatively charged sugar phosphate backbone of DNA. Roughly 147 base pairs of DNA is wrapped around a nucleosome. Each histone also consist of 20-35 amino acid residue that extends as a tail on the nucleosome surface, which help in folding the nucleosome into a further complex structure (Peterson,2004). The nucleosomes are separated from each other by 10-60 base pairs of DNA which is referred to as linker DNA (Peterson,2004). As mentioned in the lecture, DNA enters the nucleosome via H3 and exits from H4.In order to access the DNA, histone

More about INTRODUCTION Double stranded breaks (DSB) occur frequently in eukaryotic cells. It can be caused by

Open Document