Biology · Molecular Basis of Inheritance · NEET
RNA can do BOTH jobs needed for early life: it can carry genetic information (like a gene) and it can act as a catalyst to speed up biochemical reactions (like an enzyme). DNA cannot catalyse reactions on its own. NCERT also says essential life processes such as metabolism, translation and splicing evolved around RNA. So RNA came first because one molecule was enough to run early life.
A ribozyme is an RNA molecule that works as a catalyst, meaning it speeds up a chemical reaction the way an enzyme does. NCERT points out that some important biochemical reactions in living systems are catalysed by RNA catalysts, not by protein enzymes. A NEET-favourite example: the 23S rRNA in the bacterial ribosome is a ribozyme that forms the peptide bond during translation.
Because RNA is reactive and therefore unstable. A genetic material must be stable to store information safely over long time. So DNA evolved from RNA with chemical modifications that make it more stable. DNA is double-stranded and its two complementary strands let it resist changes and even repair damage, which single-stranded RNA cannot do easily.
Two reasons from NCERT: (1) DNA has chemical modifications (like the 2' deoxyribose sugar and thymine instead of uracil) that make it less reactive. (2) DNA is double stranded with complementary strands, so if one strand is damaged the other acts as a template for repair. RNA is single stranded and reactive, so it cannot resist changes as well.
No. It says the opposite. Life's information first used RNA, and DNA came afterwards, evolving FROM RNA. Do not write that DNA is the original or first genetic material in an RNA World question. The order for NEET is: RNA first, then DNA evolved from it as a stable form.
Statement I: In the RNA world, RNA is considered the first genetic material evolved to carry out essential life processes; RNA acts as a genetic material and also as a catalyst for some important biochemical reactions in living systems. Being reactive, RNA is unstable. Statement II: DNA evolved from RNA and is a more stable genetic material. Its double helical strands being complementary, resist changes by evolving repairing mechanism. Choose the most appropriate answer.
Which of the following rRNAs acts as structural RNA as well as ribozyme in bacteria?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the idea that RNA was the first genetic material on early Earth because RNA could both store genetic information and catalyse reactions, before stable DNA evolved from it.
The 23S rRNA in the bacterial ribosome is a ribozyme; it catalyses peptide bond formation during protein synthesis. This shows an RNA, not a protein, doing an enzyme's job.
RNA is reactive because of its chemistry (it has a 2' OH on the ribose sugar and is single stranded). Being reactive makes it break down easily, so it is not ideal for long-term storage of genetic information.
DNA is double stranded with complementary strands. If one strand is damaged, the cell uses the other strand as a template to repair it, so DNA can correct errors that RNA cannot.
NCERT Class 12 Biology, Chapter 'Molecular Basis of Inheritance', section 5.3 'RNA World' (around page 88). It is short but has been directly asked, for example in NEET 2025.
