Lesson 5 of 13 · 6 min
Properties of genetic material and the RNA world
NCERT § "The Search for Genetic Material" and § "RNA World"
If DNA is so much more stable than RNA, why do biologists suspect life's very first genetic material was RNA, not DNA?
The lesson in notes
In short
A genetic material must replicate itself, be chemically and structurally stable, allow slow changes (mutation) needed for evolution, and be able to express itself as Mendelian characters.
In most organisms DNA is the genetic material; in some viruses such as tobacco mosaic virus and QB bacteriophage, RNA is.
The 2′-OH in every RNA nucleotide makes RNA reactive, labile and easily degraded. RNA is also a catalyst, which adds to its reactivity.
DNA is chemically less reactive and structurally more stable. Having thymine in place of uracil also gives DNA extra stability.
Both nucleic acids can mutate, but unstable RNA does so faster; viruses with an RNA genome and a short life span therefore mutate and evolve faster.
RNA can directly code for protein synthesis and express characters easily; DNA needs RNA for this. So DNA suits long-term storage of information, while RNA suits its transmission.
RNA was likely the first genetic material. Early life processes evolved around RNA, which served both as genetic material and as catalyst; some reactions in living cells are still catalysed by RNA. DNA later took over storage because it is more stable, being double-stranded and able to resist change through repair.