DNA Structure and Replication

Q1: The nucleosome consists of histone

A tetramer and 146 bp of DNA

B octamer and 146 bp of DNA

C none of the above

D hexamer and 146 bp of DNA

ANS:A - octamer and 146 bp of DNA

The nucleosome core particle consists of 8 histones (octamer) consisting of 2 copies each of H2A, H2B, H3 and H4.

-A DNA strand of 146 base pairs is tightly wrapped around this core in two turns (73 nucleotide bp/turn).

In total, 5 types of histone proteins are present.

H2A, H2B, H3 and H4 in core particle (8 copies).

H1 in linker DNA (1 copy).

Explanation:

Nucleosome is the lowest level of chromosome organization.

Comprising of 2 parts; a core particle and a small spacer or linker DNA.

1) Core particle has histone octamer with DNA wrapped around it.

2) Spacer DNA varies between species.

One unit of H1 is associated with linker DNA.

H1 is primarily involved in packaging of nucleosomes into 30 nm fibres.



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