Origin and Evolution of Life — BIOLOGY STD 12 Science — Question

(1) RNA world hypothesis is based on discovery of catalytic RNA or ribozymes. It was proposed by Carl Woese, Francis Crick and Leslie Orgel in 1960 whereas Ribozymes were discovered by Sidney Altman and Thomas Cech in 1980.

(2) According to this hypothesis, early life must have been based most probably on RNA.

(3) Factors supporting this hypothesis are:

• RNA is found abundantly in all living cells.
• It is structurally related to DNA.
• Chains of RNA can evolve or undergo mutations, replicate and catalyse reactions.
• Biomolecules like Acetyl-Co-A have a nucleotide in their molecular structure.
• Ribosome acts as a protein assembly unit in the cell and is seen in many types of cells.
• In ribosomes, translation process is catalysed by RNA.

(4) The primitive molecules underwent repeated replication and mutation forming varieties of RNA molecules with varying sizes and catalytic properties.

(5) They later developed their own protein coats and machinery to survive the assembly of primitive cell.

(6) From them DNA was developed which was double stranded stable structure.

(7) It further kept on evolving giving rise to rich biodiversity on earth.