Nucleosome and histones

1. Nucleosome model of chromosome:
By
Harinatha Reddy A
Department of Biotechnology
Christ University
Bangalore

3. Nucleosome:

4. Introduction:
 A nucleosome is a basic structural unit of chromatin was
described by Roger Kornberg in 1974.
 Nucleosome consisting of a segment of DNA coiled in sequence
around eight histone protein cores.

5.  The nucleosome core particle consists of approximately 146 base
pairs (bp) of DNA wrapped in 1.67 times left-handed around a
histone octamer.
 Histone octamer consisting of 2 copies each of the core histones
H2A, H2B, H3, and H4.

6.  Linker histone such as H1, is bound to the DNA as it enters
each nucleosome core particle.
 Nucleosome core particle along with H1 is known as
Nucleosome (Chromatosome).
 Nucleosome which consists of 166 base pairs of DNA.

7.  Nucleosome 10 nm in size.
 Adjacent nucleosomes are joined by a 10-80 bp length DNA
termed "linker DNA“.
 The length of Linker DNA depending on species and tissue type.

8.  Histone Hl molecules appear to play an important role in this
stage of chromatin condensation.
 Histone H1 protein determining the DNA replication and
transcription.

9. Histones – types and function:

10. (Arginine, Lysine and Histidine).

11.  In biology, histones are highly basic proteins (5 Histone proteins)
found in eukaryotic cell nucleus.
 They are the chief protein components of chromatin, around which
DNA winds, and playing a role in gene regulation.
 Without histones, the unwound DNA in chromosomes would be
very long.
Introduction:

12.  Five major families of histones exist: H1, H2A, H2B, H3, and
H4.
 Histones H2A, H2B, H3 and H4 are known as the core
histones, while histones H1 are known as the linker histones.

13.  The 4 'core' histones (H2A, H2B, H3 and H4) and H1 are
relatively similar in structure .

14.  DNA and core histones are held together by several types of
noncovalent bonds, including ionic bonds.
 The bonds formed between negatively charged phosphates of the
DNA backbone and positively charged residues of the histones.