DNA and Replication — Part 1: The genetic material and its structure: visual lesson, ISC Class 12 Biology

Lesson

Molecular Basis of Inheritance

Part 1 — what the genetic material is, how it was found, and how it is built and packed.

In this lesson you will

State the properties of a genetic material
Describe the experiments of Griffith, Avery–MacLeod–McCarty and Hershey–Chase
Describe the double helix and the contributions of Miescher, Chargaff, Wilkins, Franklin, Watson and Crick
Compare DNA and RNA, name the types of RNA, and describe DNA packaging

Concept

What makes a good genetic material?

A molecule that acts as genetic material must meet four criteria.

Table of the four criteria of a genetic material
Criterion	How DNA meets it
Generate its own replica	Complementary base pairing allows exact copying
Be chemically and structurally stable	DNA lacks the reactive 2′-OH of RNA and has thymine, so it is more stable
Allow slow changes (mutation) for evolution	Base changes are rare but possible
Express itself as Mendelian characters	Through RNA and proteins

Diagram

Griffith: transformation

In 1928, Frederick Griffith worked with Streptococcus pneumoniae. S (smooth) strains have a capsule and are virulent; R (rough) strains lack it. Heat-killed S mixed with live R killed mice, and live S bacteria were recovered: R cells had been transformed.

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