MOLECULAR BIOLOGY

1. HISTONES
Ankita Behera
M.Sc Microbiology
St. George College of Management & Science
Bengaluru North University

5.  Histones contain a large proportion of the
positively charged amino acids, lysine and
arginine in their structure.
DNA wraps around histones and they also
play a role in GENE REGULATION.

9. H2A{CONTAIN MORE LYSINE:-
◦ H2A packages DNA molecules into chromatin ,the packaging process
will effect GENE Expression.
◦ They vary often by only a few amino acids.
◦ 10.9% of lysine.
◦ It plays a major role in determining the overall structure of chromatin
and has been found to regulate gene expression.
◦ Molecular weight is 13,960.

10. H2B {contain more lysine}:-
◦ It is also involved with the structure of the nucleosome of the
“BEADS ON A STRING” structure.
◦ Its molecular weight is 13,774.
◦ 16% of lysine.
◦ It is also found to regulate GENE EXPRESSION.

11. H3{CONTAIN MORE ARGINE}:-
◦ It features a main Globular domain and a long N-terminal tail.
◦ It is an important protein in the merging field of epigenetics , where
its sequence variants and variable modification states are thought to
play a role in the Dynamic and long term regulation of genes.
◦ It is in the structure of chromatin in eukaryotic cells .
◦ Molecular weight is 15,273.

12. H4{CONTAIN MORE ARGINE}:-
◦ Molecular weight is 11,236.
◦ It is the structural component of the nucleosome and is subject to
covalent modification , including acetylation and methylation which
may alter expression of genes located on DNA associated with its
parent histone octamer.
◦ Also involved in the structure of chromatin in Eukaryotic cells.

14. H1 {highest lysine/arginine ratio}:-
◦ It is not part of the nucleosome core particle instead binds to the
linker DNA is reffered as “LINKER HISTONE”.
◦ It is half as abundant a sother histones which is consistent with the
finding that only one molecule of H1 can associate with a
nucleosome.

15. Function of the histone protein in a
chromosome:-
◦ The DNA is housed in chromosomes in the form of nucleosomes.
◦ Positively charged histones are linked with negatively charged
phosphate group of DNA.
◦ It is the basic unit of chromosome or chromatin fibre.

18. It has been proposed that these
modifications results in a “code” which
can be read by proteins involved in
GENE EXPRESSION and other DNA
translation.

20. ACETYLATION
◦ Acetylation provides binding sites for a number of proteins with an approx.100
amino acids sequence most called “BROMODOMAIN”.
ACETYLATION DEACETYLATION
• HISTONE ACETYLATION • HISTONE DEACETYLATION
• Enzyme responsible for it are
“HISTONE ACETYL
TRANSFERASE”(HATs).
• Enzyme responsible for it are
“HISTONE
DEACETYLASES”(HDACs).
• Allow transcription • Repress transcription.
• Reduces positive charge and weak the
interaction of histones with DNA.
• Increases interaction of DNA and
histones.
• Adda acetyl groups to histone tails. • Removes acetyl groups from histone tails.

25. phosphorylation
◦ It is the addition of phosphate group to a molecule.
◦ It is catalyzed by various proteins “KINASES”where as phosphatase mediate
removal of phosphate group.
◦ It make the histone more negative which weakens the packing ability of histones.
◦ Phosphorylation of histones is particular H2AX has a role in DNA damage
response and DNA repair .
◦ Phosphorylation of H3S10 was linked to chromosome relaxation and
segregation.
◦ Although information is limited and is clear they can influence chromatin
structure and have a significant impact on cellular activity

26. THANK YOU