DNA is the hereditary material found in humans and most organisms. It is composed of nucleotides containing a nitrogenous base, sugar, and phosphate. The two main types of nitrogenous bases are purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil). DNA structure involves nucleotides linking to form a double helix with antiparallel strands bonded by hydrogen bonds between complementary base pairs. The three main DNA types are B-DNA, A-DNA, and Z-DNA, which differ in their helical structure, number of base pairs per turn, and handedness.

1. ASI THOMAS, M.Sc
(MEDICAL BIOCHEMISTRY),
LECTURER,
Ganga College of Nursing,
Coimbatore.

2. DNA-Types and
Structure

3. DNA or deoxyribonuclic acid is the
heriditary material in humans and almost
all organisms.
INTRODUCTION

4. NUCLEOTIDES:-
Nitogeneous base + Pentose sugar +
Phosphate

5. Nitrogeneous base + sugar
NUCLEOSIDE

6. PURINES & PYRIMIDINES
The nitrogeneous base found in
nucleotides
• Purine
•Adenosine and Guanine.
•Numbered in anticlockwise
direction

7. STRUCTURE OF PURINE

8. Pyrimidine
•Cytosine, Thyamine and Uracil.
•Numbered clockwise direction.

9. STRUCTURE OF PYRAMIDINE

10. SUGARS OF NUCLIC ACID
• RNA - D-ribose sugar
• DNA- D- deoxyribose sugar
• These two differ at their structure at
C2 position.

12. STRUCTURE OF DNA
• DNA is a polymer of
deoxyribonucleotides
• Composed of monomeric units of
–dGMP
–dAMP
–dCMP
–dTMP

14. Chargaff’s Rule
• DNA had equal number of adenine
and thymine (A=T)
• equal number of guanine and
cytosine (G≡C)

16. DNA- TYPES
• Proposed by James Watson and Francis
Crick.
• Different forms of DNA
B-DNA
A-DNA
Z-DNA

17. B-DNA
• Right handed helix
• Strands are antiparallel
• Strands interact by hydrogen bonding
• A=T
• G≡C
• Angle of interaction between base pairs
result in major groove and minor groove.

18. • Helix diameter is 20Ao
• Helix rise per base pair is 3.32Ao
• 10.4 basepair per helical turn

21. Z-DNA
• It is left handed in which helix winds
to the left in a zig zag pattern.
• Play a major role in regulation of
gene expression
• In humans Z-DNA was found to form
in actively transcribed regions of the
genome

23. A-DNA
• Dehydration of DNA drives it into the A
form, which has been shown to protect
DNA under conditions such as the
extreme desiccation of bacteria
• It is right handed
• Base pair per turn is 11

24. • Vertical rise per turn is 2.56Ao
• Rotation per base pair is +33o
• Helical diameter is 19Ao