Nuclic acids and DNA

1. Structure of DNA
(Dr.) Mirza Salman Baig
Assistant Professor (Pharmaceutics)
AIKTC, School of Pharmacy,New Panvel
Affiliated to University of Mumbai (INDIA)

4. Nucleotide

8. Watson and
Crick(1953)-
Double helix
model of DNA
vid

9. Melting and annealing
(denaturation) of DNA

10. Denaturation (Anneling)
• Two strands of DNA helix are held
togther by hydrogen bonds.
• Disruption of bonds (by change in pH
or increase in temperature) results in
sepration of strand
• Phenomenon of loss of helical
structure of DNA is known as
denaturation (anneling)

13. Melting Temperature (Tm)
• Temperature at which half of helical
structure of DNA is lost.
• Melting point of DNA is higher if it
contain more no. of G-C base
(because it have tripple bond)
• Formamide reduce destabilize H-
bond and reduce melting point.

14. Packaging of DNA

15. Ø The complexes between Eukaryotic
DNA and Proteins
Ø In Prokaryotes Proteins bound in DNA
is not found, so no Chromatin
Ø Occur in nucleus, DNA does not
exists in free space, but occur as
complex with a Protein.
CHROMATIN

16. v Chromatin contains DNA, RNA,
Histones and non/ histones proteins
v In addition calcium is also present
v Histones are the major proteins of
Chromatin
v RNA and Histones proteins are
variable between different
preparation
v Histones and DNA are always
present in a fixed ratio
CHEMICAL COMPOSITION

17. Ø They are acidic proteins which are
highly variable and heterogeneous
Ø Chromatin contains in approximately
equal mass of a wide variety of non/
histone Chromosomal proteins
Ø There are more than a thousand
different types of this proteins which
involved in DNA replication and gene
expression
NON HISTONE PROTEINS

18. v They are the major proteins of
Chromatin (containing high
percentage of basic amino acid)
v Five major types of Histone/ H1,
H2A, H2B,H3 and H4
v Extremely abundant proteins in
Eukaryotic cells and play
structural roll in formation of
Chromatin
HISTONE PROTEINS

20. o Chromatin Nucleosome Solenoid
Chromosome
o Roger Kornberg proposed the
nucleosome model in 1974
o Chromatin consists of repeating sub
unit composed of DNA and Histone
proteins
o Sub unit was termed as Nucleosome
ORGANISATION OF CHROMATIN

21. § Each nucleosome code contains
approx 140bp of DNA together with
8{Eight} molecule of Histone
§ 2{Two} each of H2A, H2B, H3B and
H4
§ 1{One} molecule of Histone H1 is
located just outside the Nucleosome
core
§ DNA is wrapped around the Histone
octomer and are connected to each
other by linker DNA

24. q The packaging of DNA with Histone
yields a Chromatin fibre approx
10nm diameter seperated by linker
DNA
q In electron microscope, this 10nm
fibre has the beaded appearance that
suggested the Nucleosome model
q This Chromatin fibre can than be
further condensed by coiling into
30nm fibre to form a super Helical
complex called Solenoid
q This result in a total condensation of
about fiftyfold.

29. Ø Metaphase Chromosome is 5000 to 10000
times shorter than equivalent amount of
DNA
Ø The metaphase Chromosome contains
Nucleosome chains coil into 300 A solenoid
structure
Ø The packaging ratio is about 40:1
Ø DNA in metaphase Chromosomes is
organised into large loops attached to a
protein scaffold
Ø This scaffold is made up of Non Histone
proteins
CONDENSATION OF CHROMATIN
INTO METAPHASE CHROMASOME

30. v Each metaphase Chromosome has
two scaffold one for each Chromatin
joined together at the centromere
region
v When the Histone are removed, the
Chromatin fibre become extended
and produce loop of about 25mm.
Chromosome

32. • These two part structure of
chromosomes are called chromatids
with each chromatid of the pair
containing one of the two identical DNA
molecules
• The structure of a chromosome just
before nuclear division made up of two
chromatids.
• The chromatids are held together at a
point called the centromere
• In humans there are 23 pairs of
chromosomes