Monday, July 27, 2020

Molecular Basis of Inheritance - cancel

6. MOLECULAR BASIS OF INHERITANCE


PROPERTIES OF GENETIC MATERIAL (DNA v/s RNA)

A genetic material must have the following properties:

  • Ability to generate its replica (Replication).
  • Chemical and structural stability.
  • Provide the mutations that are required for evolution.
  • Ability to express as Mendelian Characters.

Reasons for stability (less reactivity) of DNA

Reasons for mutability (high reactivity) of RNA

Double stranded

Single stranded

Presence of thymine

Presence of Uracil

Absence of 2’-OH in sugar

Presence of 2’-OH in sugar

-   RNA is unstable. So, RNA viruses (E.g. Q.B bacteriophage, Tobacco Mosaic Virus etc.) mutate and evolve faster.

-   DNA strands are complementary. On heating, they separate. In appropriate conditions, they come together. In Griffith’s experiment, some properties of DNA of the heat killed bacteria did not destroy. It indicates the stability of DNA.

-   For the storage of genetic information, DNA is better due to its stability. But for the transmission of genetic information, RNA is better.

- RNA can directly code for the protein synthesis, hence can easily express the characters. DNA is dependent on RNA for protein synthesis.


RNA WORLD

  • RNA was the first genetic material.
  • It acts as genetic material and catalyst.
  • Essential life processes (metabolism, translation, splicing etc.) evolved around RNA.
  • DNA evolved from RNA for stability.

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