Genetic material, Nucleotide, Nucleoside, Chargafs rule, Nucleosomes, Histones

1. Deoxyribonucleic acid
By – Agrani Paudel
Microbiology,
St. Xavie’s College
Maitighar,Nepal

2. Genetic material
• inheritable
• replicate
• Stable mutations
• translate the information by transcription
• Nucleic acid
• Discovered by Friedrich Miescher in 1869 in pus cells ;called
“Nuclein”
• Term nucleic acid was given by Altman in 1889
• DNA
• In nucleus, mitochondria and plastid in eukaryotes , in
cytoplasm in prokaryotes
• RNA
• in cytoplasm

3. Nucleic acid
• Nucleic acid = polymers of
nucleotides
• Nucleotide = nucleoside
+phosphate
• Nucleoside=sugar + nitrogen bases
• Thus, Nucleotide = phosphate +
sugar + nitrogen bases

4. Nucleotide
• Is made up of three things
• i. Pentose sugar
• ii. Nitrogen bases
glycosidic bond
• iii. Phosphate group
phosphodiester bond

5. Pentose sugar
• two types
• i. Ribose sugar
• ii. deoxyribose sugar- one oxygen
atom less at second carbon
• More the number of functional
group more reactive it becomes
but genetic material must be
stable

6. Nitrogen bases
• i. pyrimidine
• monocyclic
• 2 nitrogen atom at 1,3
• Cytosine, thymine ,uracil
• 1st carbon of sugar with 1st
pyrimidine

7. • ii. Purine
• made up of two ring of carbon ,
dicyclic
• 4 nitrogen atom at 1,3,7,9,
• Adenine , guanine
• 1st carbon of pentose sugar and
9th carbon of purine

8. Phosphoric acid
• acidic nature of nucleus ,
sugar of nucleoside
combines with
phosphoric acid by
phosphodiester bond
formed at 5th or 3rd
carbon of sugar

10. Structure of DNA
• acidic substance
• Term DNA by Zach anis
• Structure Watson and Crick
• four deoxyribonucleotides
• Deoxy adenylate (A)
• Deoxy guanylate (G)
• Deoxycytidylate (C)
• Thymidylate (T)

11. Watson and Cricks
model
• DNA double helix model (1953)
• Nobel prize in 1962
• Right handed; clockwise
• DNA helix made of two strands
(ds)
• Each strand is made up of chain
of nucleotides
• Two strands are anti parallel
;spiral staircase

12. Structure of DNA
• Purines pair with pyrimidines with
hydrogen bond A with T and C with G
• Diameter is 20Å
• One complete turn = 34Å
• 10 base pairs in one turn
• Distance between two consecutive
base pairs 3.4 Å

14. Structure of DNA
• Such nucleotides are linked together
by phosphodiester bond to form a
polynucleotide chain between the
5ʹ phosphate group of one
nucleotide and the 3ʹ hydroxyl
group of another.
• A nucleic acid strand has a free
phosphate group at the 5ʹ end and
a free hydroxyl group at the 3ʹ
end.

15. Structure of DNA
• Nitrogenous base is attached
to 1’ carbon of sugar. At this
place purine base is attached
by its 9’position and
pyrimidine by its 1’position
• Polynucleotide strand is made
up of backbone of sugar and
phosphate forming its long
axis and bases at right angles
to it

16. Structure of DNA
• Two polynucleotide strand are
complementary to each other
• Two such complementary strand are
joined with another by hydrogen
bonds between their complementary
nitrogenous bases.

17. Structure of DNA
• There are three hydrogen
bond between cytosine
and guanine and two
hydrogen bonds between
adenine and thymine
• The two chains or strands
are antiparallel

18. Chargaff's rule
• Chargaff’s rule (1950) only for double stranded not for singe stranded structure
• Purine = pyrimidine i.e. A+G= T+C
• Sugar deoxyribose and phosphate occur in equimolar proportions
• A+T/G+C is constant for a species
• A and T are equal
• C and are equal to G

19. Types of DNA
• On the basis of function
• Trophic –all activities except reproduction
• Genetic =reproductive
• E.g. Paramecium macro nucleus- trophic DNA
• Micro nucleus = genetic DNA
• On the basis of no of base pair and turn and coiling

20. • Nucleosomes, histones
• Heat or chemicals can break the hydrogen
bonds between complementary bases,
denaturing DNA. Cooling or removing
chemicals can lead to renaturation or
reannealing of DNA by allowing hydrogen
bonds to reform between complementary
bases.
• DNA stores the instructions needed to
build and control the cell. This information
is transmitted from parent to offspring by
vertical gene transfer