Question

What is nucleosome? Explain the packaging of DNA helix. Draw the labelled diagram of nucleosome.

Answer 1

A nucleosome is the system used for DNA packaging in eukaryotes. The system is made by winding the DNA around eight histone protein cores. There are five types of histone proteins, H1, H2A, H2B, H3 and H4. Four of them (H2A, H2B, H3 and H4) occur in pairs to produce histone octamer, called nu body or core of nucleosome. H1 protein is responsible for linking two octamers. This nucleosome combines to form a solenoid. The solenoid defines the packing of DNA as a 30 nm fibre of chromatin and results from the helical winding of at least 5 nucleosome strands. This solenoid is coiled and supercoiled to form a compact structure which can be packaged inside the nucleus.