Abstract:
The information required for the sustenance of life is encoded in the form of DNA in
most organisms except certain viruses where RNA is the genetic material. This information
stored in the DNA is decoded in the form of RNA by the cellular transcriptional machinery.
The language of transcriptional readout is subsequently translated into peptide sequence by
cellular ribosomes and associated protein synthesis machineries. The eukaryotic genome
ranges from around 12.49 x 106 bp (5,770 genes) in budding yeast to 3.3 x 109 bp (several
thousand megabases coding for ~20,500 genes) in humans. This huge genetic material
spanning upto 2 meters in humans is accommodated inside the nucleus with the help of
several tiers of packaging, which requires the wounding up of DNA (~146 bp) around a
core of histone proteins forming the nucleosome. This nucleo-protein complex or
nucleosome forms the structural unit of chromatin. The chromatin folds further in a definite
pattern and results in a highly compact and dense organization of the genome (Fig. 1.1).
Though this chromatin organization makes it seemingly rigid, its fluidity is maintained by
several cellular players which aid in the accessibility of the chromatinized DNA to several
cellular processes such as transcription, replication and repair.
