Molecular Basis of Inheritance

Notes

Introduction

Every living organism inherits genetic information from its parents. This genetic information is stored in DNA (Deoxyribonucleic Acid).

The Molecular Basis of Inheritance explains:

Structure of DNA

RNA and its types

DNA replication

Transcription

Genetic code

Translation (Protein synthesis)

Gene regulation

Human Genome Project

DNA Fingerprinting

Important Scientists

Scientist Discovery

Friedrich Miescher Discovered DNA (1869)

Griffith Transformation experiment

Avery, MacLeod & McCarty DNA is genetic material

Hershey & Chase Confirmed DNA as genetic material

Watson & Crick Double Helix Model

Chargaff Base pairing rules

Meselson & Stahl Semi-conservative replication

Jacob & Monod Operon Model

Har Gobind Khorana Genetic code

Marshall Nirenberg Deciphered genetic code

DNA (Deoxyribonucleic Acid)

DNA is the hereditary material in almost all organisms.

Components of DNA

Each nucleotide contains:

Deoxyribose sugar

Phosphate group

Nitrogen base

Nitrogen Bases

Purines

Adenine (A)

Guanine (G)

Pyrimidines

Cytosine (C)

Thymine (T)

Structure of DNA

Watson and Crick proposed the Double Helix Model (1953).

Features

Two polynucleotide chains

Right-handed helix

Antiparallel strands

Sugar-phosphate backbone outside

Nitrogen bases inside

Base Pairing

A = T (2 Hydrogen Bonds)

G ≡ C (3 Hydrogen Bonds)

Dimensions of DNA

Diameter = 2 nm

Distance between base pairs = 0.34 nm

One turn = 3.4 nm

Base pairs per turn = 10

Very Important for Board Exams

Chargaff's Rule

A = T

G = C

Purines = Pyrimidines

Packaging of DNA

Prokaryotes

DNA is circular.

Located in nucleoid.

Eukaryotes

DNA wraps around histone proteins.

Forms nucleosomes.

Chromatin → Chromosome

Search for Genetic Material

Griffith Experiment

Used:

Streptococcus pneumoniae

Found

Transformation Principle

Avery, MacLeod & McCarty

Showed that DNA is transforming principle.

Hershey & Chase Experiment

Virus

Bacteriophage

Radioactive markers

³²P → DNA

³⁵S → Protein

Conclusion

DNA is genetic material.

RNA

RNA contains

Ribose sugar

Phosphate

Bases

A

U

G

C

(Uracil replaces Thymine)

Types of RNA

mRNA

Carries genetic message.

tRNA

Transfers amino acids.

Adaptor molecule.

rRNA

Forms ribosomes.

Most abundant RNA.

DNA Replication

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