Biochemical or Oparin haldane's ( Most accepted theory regarding the origin and evolution of life. )
(From Origin and evolution of life)
This theory is the most accepted theory regarding the origin of life. It was purposed by Russian scientist called Alexander Ivanovich Oparin in 1923 A.D and supported by British biochemist John burden Sanderson Haldane after 5 years in 1928 A.D. So, this theory is also known as Oparin Haldane's theory of Biochemical origin of life.
According to Oparin "Life on Earth originated from some non living organic substance found in ocean of primitive earth about 3.3 billion years also."
This is the most complex phenomenon so it has been divided into 3 steps and they are:
1. Chemogeny
2. Biogeny
3. Cognogeny
Chemogeny
It involves the formation of chemical molecule. It has following sub steps :
a. Formation of Methane, water, ammonia
In the primitive atmosphere of the earth, the element like H,C,N,O were found abundantly. Due to extreme temperature of the earth they were found in gaseous state. But gradually the earth cooled down and these element combined to form methane, water and ammonia.
2H 2+O2-----------> 2H 2O
C+H 2------------> CH 4
N 2+3H2 ------------> 2NH3
b. Formation of Hydrocarbons
When the temperature of the earth cooled to 100 C or even below that, the free organic radical like -CH and -CH2 in the atmosphere combined to form saturated and unsaturated hydrocarbons.
CH + CH-----------> CH 2 (Acetylene)
CH2 + CH 2---------> C2 H4 (Ethylene)
CH2 + CH2 ----------> CH 4 + C (Methane)
c. Formation of oxy and hydrooxy derivative of Hydrocarbon
The above formed hydrocarbons reacted with the super heated steam (H2 O) to form oxy and
hydrooxy derivative of hydrocarbons.
C 2H2 + H 2O ------------> CH 3CHO (Acetaldehyde)
d. Formation of sugar, fatty acid , nucleic acid
Due to reduction, condensation, oxidization, polymerization all the above molecule reacted with each other to from sugar, fatty acid and Amino acid.
CH 4 + H2O -------------> Sugar
CH + H2 O + NH3 ----------> Amino acid
e. Formation of purine , pyrimidines and nucleotides
All the above molecules formed in oceanic water reacted to form purine, pyrimidines and nucleotide. The energy sources for the reaction were provided by heat from extreme temperature of the earth, electric discharge from lighting and uv-rays from
sun.
Oparin called oceanic water as "Prebiotic" or "Premordial" or "Hot dilute soup"
Biogeny (Formation of Self reproducing biological molecules)
It has following substeps :
a. Formation of DNA, RNA
Sugar, phosphate, purine pyrimidine combined to form nucleotide and nucleotide combined to form nucleic acid which gave rise to DNA and RNA. Formation of DNA and RNA was the important step for the formation of life.
b. Formation of coacervates
DNA and RNA formed in oceanic water reacted with the molecules of oceanic water to form self reproducing mass bounded by water layer known as coacervates. Oparin called it living molecule. According to him it was intermdeiate between the molecule and organism. It was precell or eobiont.
c. Formation of primary organism
Coacervates absorbed the inorganic substance found in oceanic water, grew in size and
muliplied to form first cell protocell. Oparin called it Protocell. It was anaerobic heterotrops. It was similar to virus which gave rise to two different kind of cell
i.e :
Prokaryotic cell :
Cell without definite nucleus(Don't contain nucleoplasm, nucleolus , nuclear membrame) and DNA is naked. Eg : Monera
Eukarotic cell :
Cell with definite nucleus. Eg : Protista
Monera evolved into bacteria or cynobacteria etc whereas protista developed into metazoa, metaphyta, potozoans.
Cognogeny (Mechanism of evolution of perception, expression, communication and feeding)
It is last step of Biochemical theory. It involves the diversification of Metazoa, Metaphyta and protozoa. Due to shortage of food they adopted different method of feeding to obtain food. Some became parasitic, saprozoic, some chemo synthesizer and some photosynthetic etc.
Those organism which could prepare their own food led to auto tropic nutrition where as organism which were unable to prepare their own food led to hetero tropic nutrition.
origin of life
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