Question

The first formed organism (ribo-organism) used only .............. for catalyzing reactions.

• A. DNA
• B. Amino aicds
• C. Fatty acids
• D. RNA

Answer 1

The correct option is D RNA

Amino acids and fatty acids do not have catalytic properties and hence cannot serve as genetic material which makes options B and C incorrect. Nucleic acids were formed in primitive hot soup of sea by formation of pyrimidine-sugar –phosphate and purine-sugar-phosphate. RNA has ability of self replication and to catalyze other chemical reactions. As we know that rRNA in present day organisms serves as catalyst in peptide bond formation during protein synthesis. Presence of ribozymes (the RNA molecules that serve as enzymes) and sequence homology in prokaryotic and eukaryotic rRNA confirm evolution of their catalytic function earlier during evolution. Thus, RNA served as enzymes in first life forms. Though, both RNA and protein had catalytic activities, RNA extended their functions to self replication while proteins continued to serve as enzymes. This makes option D correct. Switching from RNA to DNA, as a genetic material, was favoured later due to less susceptibility of double stranded DNA molecules to breakage and mutations as compared to that of single stranded RNA. Error prone replication of single stranded RNA provided raw material for evolution of different organisms from primitive organisms. Thus, DNA did not serve as catalyst. Option A is incorrect.

Therefore, the correct answer is option D.