05 Origin and Evolution of life - part 03 - Urey and Miller's Experiment - RNA World Hypothesis

05 Origin and Evolution of life - part 03 - Urey and Miller's Experiment - RNA World Hypothesis

Urey and Miller's Experiment : 

• Stanley L.Miller and his teacher Harold C.Urey provided the first experimental evidence in support of chemical evolution theory of Oparin. 
• They designed a glass-apparatus called spark-discharge apparatus. 
• The apparatus  was first sterilized and evacuated.
•  Methane, ammonia and hydrogen gases were pumped in the proportion of 1:2:2 into the glass chamber. 
• A tube carrying water vapour was also connected to the chamber. 
• Lightning effect was mimicked by electric discharge carbon arc spark in the chamber. 
• Process of evaporation and precipitation was also simulated by the use of heating mantle and condenser respectively. 
  
• The mixture ofCH4, NH3, H2was exposed continuously to electric discharge for several days causing the gases to interact, after which these were condensed. 
• The liquid collected in the U-tube turned brown. 
• Chemical analysis of this liquid reported the presence of simple organic compounds. (urea, amino acids, lactic acid, etc). 
• This experiment strongly supports that the simple molecules present in the earth's early atmosphere combined to form the organic building blocks of life.

RNA World Hypothesis : 

• Oparin Haldane theory and Miller Urey experimentgives us an understanding that pathway of origin of life on earth goes from non-living to living. 
• `Like begets like' necessitates presence of stable genetic material and cellular machinery to carry out routine activities essential for survival. 
• We are also aware that certain proteins which we call enzymes, catalyse the chemical reactions in the cell. 
• It was in 1980 that Sidney Altman and Thomas Cech independently found out that RNAs can also act as biocatalysts. These catalytic RNAs are called as Ribozymes. 
• For this discovery, Altman and Cech earned Nobel Prize in chemistry in 1989. This discovery provided important support for RNA World hypothesis. 
• The hypothesis suggests that early life must have been based exclusively on nucleic acids, most probably RNA. 
• It was first proposed by Carl Woese, Francis Crick and Leslie Orgel in 1960, long before discovery of ribozymes. 
• Fact is that RNA is found abundantly in all living cells, it is structurally related to DNA and chains of RNA can evolve or undergo mutations, replicate and catalyse reactions, all support this hypothesis.
• Besides, biomolecules like Acetyl-Co-A have a nucleotide in their molecular structure. 
• Major evidence is existence of ribosome (the protein assembly unit) in the cell. In ribosomes, translation process is catalysed by RNA.
• These molecules might have undergone repeated replication and mutation forming varieties of RNA molecules with varying sizes and catalytic properties. 
• Eventually they might have developed their own protein coats and machinery to survive the assembly of primitive cell. 
• In due course, a double stranded stable structure, the DNA, might have been formed and thus continued the ongoing journey which resulted in rich biodiversity on earth.