Write a comparative note on the properties of $DNA$ and $RNA$.

(N/A) From the Hershey-Chase experiment,it became an established fact that $DNA$ acts as the genetic material.
However,it subsequently became clear that in some viruses,$RNA$ is the genetic material (e.g.,Tobacco Mosaic Virus,$QB$ bacteriophage,etc.).
$A$ molecule that acts as genetic material must fulfill the following criteria:
$(i)$ It should be able to generate its replica (Replication).
$(ii)$ It should be chemically and structurally stable.
$(iii)$ It should provide the scope for slow changes (mutation) required for evolution.
$(iv)$ It should be able to express itself in the form of 'Mendelian Characters'.
Comparing these requirements:
- Due to the rule of base pairing and complementarity,both nucleic acids ($DNA$ and $RNA$) have the ability to direct their duplication.
- Proteins fail to fulfill the first criterion.
- Stability: Genetic material must be stable enough not to change with different stages of the life cycle,age,or physiology. Griffith's experiment showed that heat did not destroy the properties of the genetic material $(DNA)$.
- Chemical Stability: In $RNA$,the $2'-OH$ group present at every nucleotide is a reactive group,making $RNA$ labile and easily degradable. $RNA$ is also catalytic,hence more reactive.
- $DNA$ is chemically less reactive and structurally more stable than $RNA$. The presence of thymine instead of uracil also confers additional stability to $DNA$.
- Mutation: Both $DNA$ and $RNA$ can mutate. $RNA$ being unstable,mutates at a faster rate. Consequently,viruses with $RNA$ genomes evolve faster.
- Expression: $RNA$ can directly code for protein synthesis,whereas $DNA$ depends on $RNA$ for protein synthesis. The protein-synthesizing machinery has evolved around $RNA$.
Conclusion: Both can function as genetic material,but $DNA$ is preferred for the storage of genetic information due to its stability,while $RNA$ is better for the transmission of genetic information.