A typical mammalian cell has 22 metres long DNA molecule whereas the n

1.	A typical mammalian cell has 22 metres long DNA molecule whereas the nucleus in which it is packed measures about 10–6 m. Explain how such a long DNA molecule is packed within a tiny nucleus in the cell.
Answer» Packaging of DNA in eukaryotes • The proteins associated with DNA are of two types—basic proteins (histone and protamine) and acidic non-histone chromosomal (NHC) proteins. • The negatively charged DNA molecule wraps around the positively charged histone proteins to form a structure called nucleosome. • The nucleosome core is made up of four types of histone proteins—H₂A, H₂B, H₃ and H₄— occurring in pairs. • 200 bp of DNA helix wrap around the nucleosome by 1¾ turns, plugged by H₁ histone protein.

A typical mammalian cell has 22 metres long DNA molecule whereas the nucleus in which it is packed measures about 10–6 m. Explain how such a long DNA molecule is packed within a tiny nucleus in the cell.

Answer»

Packaging of DNA in eukaryotes

• The proteins associated with DNA are of two types—basic proteins (histone and protamine) and acidic non-histone chromosomal (NHC) proteins.

• The negatively charged DNA molecule wraps around the positively charged histone proteins to form a structure called nucleosome.

• The nucleosome core is made up of four types of histone proteins—H₂A, H₂B, H₃ and H₄— occurring in pairs.

• 200 bp of DNA helix wrap around the nucleosome by 1¾ turns, plugged by H₁ histone protein.