B.Sc BIOTECHNOLOGY
SRI HARSHINI DEGREE & PG COLLEGE.
ONGOLE-523001.
Dr Vemu Anil kumar M.Sc, Ph.D.nanobiotechanil@gmail.com

RNA – Ribo Nucleic acid
DNA – Deoxy Ribo Nucleic acid
• JOSPEH FREDERICK MEISCHER – First isolated NAs from
pus cells – Nuclein.
• ALTMAN – Nucleic Acid.
NUCLEIC ACIDS
Constituents:
1.Phosphoric Acid.
2.Pentose sugar.
3.Organic Base – Nitrogen Base.

• It has THREE reactive hydroxyl groups (-OH).
• TWO are involved in Sugar – Phosphate back bone for DNA
• ONE binds with 5’ C and the other 3’ C of PENTOSE SUGAR
- Phospho Diester Linkage.
• 5’ C – O – P – O – 3’ C
1. PHOSPHORIC ACID (H3PO4).

Phospho Diester Linkage

2. PENTOSE SUGAR.
• DNA : 2’ Deoxy – D – Ribose.
• RNA : D – Ribose.
• Why prime ?
• ………!!

• Two types : (i)PURINES (ii) PYRIMIDINES.
(i) PURINES : Two ring structure.
• One – Six membered Pyrimidine ring (similar to Benzene)
1 and 3 positions are Nitrogen.
• Other – Five membered Imidazole ring.
7 and 9 positions are Nitrogen.
• Nitrogen of 9th position - COVALENT LINKAGE – 1’C of
RIBOSE sugar.
3. Organic Base – Nitrogen Base.

(ii) Pyrimidines :
Single ring structure.
• 1 and 3 positions are Nitrogen.
• 2 position KETO (=O).
• Nitrogen of 1st position - COVALENT LINKAGE - 1’C of
RIBOSE sugar.

Nucleosides:
• Nitrogen bases linked to Pentose sugar by ß- glycosidic
bond.
• In case of Purines : N-9 bond with C-1’: N-9 glycosides.
• Pyrimidines : N-1 bond with C-1’: N-1 glycosides.
• N Base + Ribose = Ribonucleoside – Purines : Adenosine,
Guanosine, Uridine, Cytidine, thymidine.
• N Base + DeoxyRibose = Deoxyribonucleoside – Deoxy
adenosine………

Adenosine :
Practice the other structures….

Nucleotides:
• Nucleoside + Phosphate.
• Phosphate attached to 5’C of Ribose.
• 5’ adenylic acid, 5’ guanylic acid, 5’ cytidylic acid, 5’ uridylic
acid : Ribonucleotides or Ribotides.
• Similarly with Deoxyribonucleotides or deoxyribotides.
• Phosphate also attached to 3’C of Ribose to form linear
polymer of Nucleotides by : Phopshodiester linkage : Back
bone having 5’ at one end and 3’ at other end (5’ 3’
direction).

Chargaff’s Rule:
• Erwin Chargaff in 1940- Chargaff’s rule of molar equivalence.
1. Py Bases (C+T) = Pu Bases (A+G).
2. Equivalence : Bases having AMINO Group at 4th or 6th
position (A+C) and Bases having KETO Group (T+G).
3. Quantity of A=T, G=C.

Watson and Crick model (B - DNA)
X- Ray Crystallography technique – Wilkins and Franklin –
Purified DNA.
1. Multistranded fibre with 22 Ao Diameter.
2. Gaps at 34 Ao.
3. Repeating units at 3.4Ao.
FOUNDATION FOR DOUBLE HELICAL STRUCTURE OF DNA

Watson and Crick model (B - DNA)
X- Ray Crystallography technique – Wilkins and Franklin –
Purified DNA.
1. Multistranded fibre with 22 Ao Diameter.
2. Gaps at 34 Ao.
3. Repeating units at 3.4Ao.
FOUNDATION FOR DOUBLE HELICAL STRUCTURE OF DNA
Lets watch…!

DOUBLE HELICAL STRUCTURE
OF DNA….

• DNA is made up of Two polynucleotide strands.
• Two strands are Anti-parallel to each other, (5’ 3’) (3’ 5’)
• Why antiparallel ? Hydrogen Bonds – Two strands.
• A=T, GΞC – Complementary Base pairing.
• Two strands are coiled in Right-Hand helix.
• Diameter – 20 A0.
• Pitch – 34 A0 – 10 Base pairs – 3.4A0 – Angle is 360.
• Minor groove and Major groove – Protein Interaction.
• Template strand – Genetic information.

Character B-Form A-Form Z-Form C-Form
Helix Direction Right Handed Right Handed Left Handed Right Handed
Base pairs per turn 10 11 12 9.33
Vertical rise per bp 3.4 Å 2.56 Å 19 Å 3.32 Å
Rotation per bp +36° +33° -30° +36°
Helical diameter 20 Å 23 Å 18 Å 19 Å
Types of DNA

Forces stabilising Nucleic acid strucutures
1. Hydrogen Bonds.
2. Base stacking.
• Hydrophobic associations.
• London dispersion forces.

1. Hydrogen Bonds:
• In general a hydrogen bond is formed if a hydrogen atom connects two
atoms of higher electronegativity.
• Under the influence of a hydrogen bond, the H becomes more
electropositive and adjacent two atoms becoming more negative. This
affect increases the affinity of atoms for H and strengthens the interaction.

2. Base stacking :
Hydrophobic associations:
• If a hydrophobic base is dissolved in water, the water molecules surround
it to form a Cluster.
• H2O cannot form H-bonds with the non-polar base.
• Hydrophobic effect in helix formation is by solvent interactions upon
folding the non-polar bases into the helical structure.
London Dispersion forces:
• Van der-walls interactions.
• Due to the formation of Dipoles, atoms interact with each other.

Thank you