Was there an ‘RNA world’ in primitive earth before takeover by DNA as genetic material? (RNA world Hypothesis)
Crick and others firmly believed about the idea of a primitive RNA world or RNA as genetic material or master molecule before the takeover by DNA.
Essential quality of a genetic material:
- Information storage and replication
Justification: Even now, RNA is the genetic material in some viruses suggesting the capacity of RNA in storing information just like DNA
But the major question who did the function of proteins (the catalytic function)?
The discovery of ribozymes further supports ‘RNA world’ that is RNA can do the function of protein or catalysis. The catalytic ability of RNA may be later passed on to the proteins. The reason for catalytic activity in RNA may be due to the presence of 2’ OH group where in DNA it is 2’H.
Now moving into the details of ribozymes
Definition: Ribozymes are RNA molecules with catalytic activity
Discoverer: Thomas Cech et al in 1983.
The first ribozyme to be discovered was spliceosomes or self splicing intron in the ribosomal rRNA genes of the ciliated protozoan Tetrahymena thermophila
Later Sidney Altman discovered ribozymes in in bacteria, Ribonuclease P an enzyme of bacteria consists of RNA and protein where RNA is found to have catalytic activity. Ribonuclease P is involved in sizing of large RNA precursors into smaller RNAs (RNA processing)
Ribozymes can form three dimensional structures just like proteins and can bind specifically to substrates and cofactors
Based on function there are two types of ribozymes
- Ribozymes that catalyse reactions on themselves or intra-molecular catalysis
- Ribozymes that catalyse other molecules without undergoing any change or inter-molecular catalysis
Cellular reactions catalysed by ribozymes
- The maturation of hnRNAs or RNA processing (spliceosome)
- Splicing of unwanted sections from primary RNA transcripts of ribosomal RNA synthesizing genes
- The formation of peptide bonds during synthesis of polypeptide chains (peptidyl transferase).
- Ribozymes catalyse the degradation of other RNAs therefore can be used as potential pharmaceutical agents against viral RNAs
- As an anticancer agent to degrade RNAs from oncogenes
Disadvantage: Ribozymes are easily degraded inside the body by various enzymes. So ribozymes are encapsulated in liposomes and is introduced into the body.