This document discusses the structure and history of discovery of DNA. It provides details on: 1) Nucleic acids being polymers of nucleotides composed of nitrogenous bases, sugars, and phosphates. Friedrich Miescher first identified nuclei. 2) Watson and Crick proposing the double helix structure of DNA in 1953 based on prior work by Chargaff, Wilkins, Franklin showing DNA resembles a coiled helix. 3) DNA being composed of nucleotides containing a sugar (deoxyribose), phosphate group, and nitrogenous base that form the double helix structure through base pairing between adenine-thymine and guanine-cytosine.

1. Submitted by: Payal ratdiya
M.Sc. Microbiology sem I
Submitted to:- Dr. Sonia kaura

2. NUCLEIC ACID
• Nucleic acid are polymer of nucleotide.
• Friedrich miescher first time identified Nuclei.
TYPES
DNA RNA
Deoxyribonucleotide acid Ribonucleic acid

3. Discovery of DNA
Avery,Macloed,Maccarty
• These scientist repeated Griffith ‘s experiment of
transformation.
• DNA digesting enzymes destroy all transforming
ability.
• Supposed DNA is the genetic material.

4. History of discovery of DNA structure
Maurice Wilkins and Rosalind Franklin
(1952)
• a. Used a method called x-ray
diffraction to take pictures of DNA
molecules.
• b. showed that DNA
resembled a tightly
coiled helix composed of
chains of nucleotides.

5. Erwin chargaff
• Suggested two rules
• that help the discovery of double
structure of DNA.
• First rule is the amount of purine is equal to amount
of guanine.
• Second rule is that the relative amount of guanine
,cytosine,adenine ,thymine is vary to organism to
organism. {A+T/G+C}

6. Watson and Crick(1953)
• a.Used Chargaff ,Wilkins,and Franklin observation
to develop their DNA model.
• b.They proposed that DNA is made to two chains
that wrap around each other in the shape of double
helix,proposed Bform of DNA

7. DNA Structure:-
• DNA stands for Deoxyribonucleic acid.
• Made up of building blocks (monomer) called
nucleotides.

8. NITROGENOUS BASE:
PURINE PYRIMIDINE
6 membrane ring
Adenine
Guanine
5 membrane ring
Thymine
Cytosine

9. Sugars
• 2 types of pentose sugar: ribose and
deoxyribose
ribose nucleic acid
absence of OH group at 2 C
Ribose
Absence of 2’OH group at 2C

10. Phosphoric acid
• Biologically called as phosphate
• Contain 3 reactive hydroxyl group
• Involved in formation of phosphodiester bond
• a. Sugar +base = Nucleoside
• b.Sugar +Base +phosphophate =Nucleotide

11. DNA Structure
To form polynucleotide structure of DNA and
RNA nucleotides are linked together by
phosphodiester bonds which formes between the
phosphate group which is attached to 5C of sugar of
one nucleotide and 3C of another nucleotide.5’-3’
phosphodiester bond form.
Nitrogen bases are attached to the first carbon
of the pentose sugar by covalent bond.

12. Watson and Crick model
Used X ray diffraction technique to proposed model .DNA is a
double stranded molecule that is twisted into a helix
• Chains are antiparallel
Bases are joined by hydrogen bond Adenine= Thymine
• Guanine = Cytosine

13. Diameter of helix 20⁰A
• One strand oriented in 5’ to3’D and another
strand is oriented in 3’ to 5’D.
• 10 base pair present in per turn.
• The interaction between base and sugar form
grooves . Major groove [large angle between
base and sugar] and Minor groove [naarow
angle between base and sugar]

14. Different types of DNA
Parameter A-DNA B-DNA Z-DNA
Helix sense
right-
handed
right-
handed
left-
handed
Residues per turn 11 10.5 12
Helix pitch(°) 28 34 45
Base pair tilt(°) 20 6 7
Rotation per residue (°) 33 36 30
Diameter of helix [Å] 23 20 18
Glycosidic Bond configration
anti anti
syn