This document provides an introduction to molecular biology, specifically discussing nucleic acids, DNA, RNA, and their roles in transcription and translation. It defines nucleotides, nucleic acids, and their components. It describes the classic Watson and Crick model of DNA structure, including its double helix shape, base pairing through hydrogen bonds, and antiparallel strands. It also summarizes DNA replication as semi-conservative and using each strand as a template. Finally, it contrasts key features of DNA and RNA such as their location in the cell, sugar composition, and roles in protein synthesis.

1. Shadi Abdul Kader EL Farran
BSc. Medical Laboratory Technology
Government Medical College, Thiruvananthapuram
2009- 2011 Batch MSc. Molecular Biology
University of Madras
Introduction to
Molecular Biology

2. Nucleic acid
 Biomolecule.
 Nucleotide is the monomer of nucleic acid.

3. Nucleoside
 Consist of:-
- Pentose sugar.
- Nitrogenous base.

4. Nucleotides
 Nucleoside mono phosphate.
 It consist of:-
-Pentose sugar.
-Nitrogenous base.
-Phosphate group.

5. Pentose sugar
 Ribose in RNA.
 2-deoxy ribose in DNA

6. Nitrogen bases:-

7. Nomenclature of Nucleosides
Adenine Guanine Cytosine Thymine Uracil
Ribose Adenosine Guanosine Cytidine Thymidine Uridine
Deoxy
ribose
Deoxy
adenosine
Deoxy
guanosine
Deoxy
cytidine
Deoxy
thymidine
Deoxy
Uridine
When it is a nucleotide add monophosphate after the name

9. Deoxyribonucleic
Acid (DNA)

10. DNA
 The universal carrier of genetic materials.
 Contains the information necessary to form all the
proteins needed in order to survive.
 Mainly seen in nucleus.
 Nitrogen bases are: Adenine, Thymine, Guanine,
Cytosine.
 Sugar is 2-deoxy ribose.

11. Structure of DNA

12. Watson & Crick model of DNA
 Introduced in 1953.
 DNA is in the form of a
regular helix containing
two polynucleotide
chains connected to each
other by hydrogen
bonds.

13. Watson & Crick Model
(DNA is polar)
 Right handed double
helix.
 Chargaff’s base pairing
rule.
 Hydrogen bonding.
 Antiparallel.
 Each strand acts as
template during
replication.

14. DNA REPLICATION

15. Introduction
 During cell division, Each daughter cell will get
the exact copy of DNA that the mother cell had.
 Process of copying DNA (replication).
 Semi-conservative.

16. Features
 Each strand serve as template for the synthesis of other
strand.
 Base pairing rule is always maintained.
 Synthesis of each strand is from 5’ to 3’ (template is
read from 3’ to 5’).
 Semi-conservative.
 The enzyme DNA polymerase synthesise the
complimentary strand by adding corresponding nucleotide.

18. RIBONUCLEIC
ACID (RNA)

19. Introduction
 They are usually single stranded polymers of
nucleotides.
 Distribution:-
50% in ribosomes and endoplasmic reticulum
25% in cytoplasm
15% in mitochondria
Rest in nucleus.

20. RNA DNA
Seen mainly in Cytoplasm Nucleus
Number of bases 100-5000 Millions
Strand type Generally single
stranded
Double stranded
Sugar Ribose 2-deoxy ribose
Bases Adenine, Guanine,
Cytosine, Uracil
Adenine, Guanine,
Cytosine,
Thymine
Chargaff’s rule Not Implemented Implemented
Sensitivity to Alkali Easily destroyed Resistant

21. What is Transcription & Translation?
 The process by which the cell can form the
proteins necessary for its functions.

22. General Overview
 DNA unwinds at the site of gene.
 Gene is copied (mRNA is formed).
 mRNA goes to ribosome.
 Each 3 nitrogen bases (codon) of mRNA represents an
amino acid.
 Translation takes place as tRNA carries amino acids
corresponding to mRNA sequence.