Q. 16: Write an account of modern self-assembly theory?

Ans.:1) The theory was given by Fox (1968), Lininger (1970) and Fox and dose (1972).

2) The theory is based on the concept that origin of life on earth i.e. protobiogenesis is because of inherent capacity of chemical meticulous to organize themselves.

3) Fox, gave model for the support of theory. The model included primary events of conversion of macromolecules.

Fox also stated that these events are fast, simple and occur frequently on the earth surface.

4) Schmitt (19560) provided first clear cut demonstration through synthesis of collagen from macromolecules.

5) Reed in 1967 gave intermolecular assembly by combining two protein molecules which resulted into enzymatically active complexes.

6) Later on it was suggested by frankel conrai and Ram Chandran (1959) and Casper (1963) that proteins and nucleic acid from TMV also for such assembly.

7) The accepted model of protobiogenesis suggests that information or proto information flowed from amino acids in the geochemical matrix to protein in the first organism.

Q. 17: Explain in brief the concept of chemical evolution of life.

Ans.: (1) Origin of life is an outcome of progressive change in chemicals.

(2) First life came into existence as a result of continuous chemical reactions, Combination in chemical compounds.

(3) This concept of origin of life is self-assembly theory of origin of life or chemical evolution of life.

(4) The theory is also known as molecular evolution.

(5) The theory was proposed; by Haeckel but it was developed by oparin and Haldane.

Q. 18 :  Explain Oparin – Haldane theory of chemical evolution

Ans. : The theory suggests that life gradually arose from abiotic components about 3.5 billion year ago through chemical evolution.

The different step which probably took place during chemical evolution  can be explained as follows:-

A) Origin of earth and its primitive atmosphere:

1) Origin of earth is in the form of broken piece from sun nearly 4.6 billion years ago and is directly related with the origin of life.

2) Primitive earth showed nebulous and pieces of rocks. Nebulous is hot gases, vapours of various elements, pieces of metals etc.

3) Due to condensation earth changed into solid state from liquid state in due course of time.

4) The heavy elements like nickel, iron got deposited to earth center forming a solid core of earth. The lighter elements like He, H, C, O2, N etc. escaped into atmosphere.

5) Thus, atmosphere of primitive earth was reducing type and no free oxygen was available.

B) Formation of Ammonia, water and methane:

1) Primitive earth showed abundant of amount of N, C, O, and H of which Hydrogen being active combined with other to form ammonia, methane and water in the form of steam.

Due to cooling of earth steam condensed into water which was accumulated in river and oceans.

Thus, NH3, H2O and CH4 are the first compound or chemicals formed on the earth surface.

C) Synthesis of simple organic compounds:

1) Due to continued cooling of earth free radicals like CH and CH2 condensed forming different macromolecules.

2) These macromolecules were hydrocarbons of both saturated and unsaturated type.

3) These macromolecules showed different chemical reactions like condensation, oxidation, reduction,   polymerization etc. with ammonia and water.

The energy for such reactions was used from like rays, radiations, lightening etc.

4) All such reactions finally resulted in the formation of monosaccharides, amino acids, nitrogen bases, and fatty acids etc. which are of immense biological importance.

5) Haldane described the sea containing molecules as the hot dilute soup or primitive broth.

6) Due to absence of free oxygen enzymes molecules never showed degradation.

D) Formation of complex organic molecules:

1) The hot dilute soup was sterile and oxygen free.

2) The different molecules or simple organic (compounds) substances collided, reacted or showed aggregation to form complex molecules like polysaccharides, fats, proteins, nucleosides and nucleotides.

3) Amino acid showed polymerization to form proteins.

4) The proteins carried out enzymatic reactions and were termed as protoproteins. These substances accelerated the rate of reactions.

E) Formation of nucleic acid:

1) The synthesis of nucleic acid took place by aggregation of compounds like sugars, nitrogen bases and phosphoric acid.

2) This resulted in different combinations called as nucleotides.

3) Polymerization of nucleotides produced nucleic acids which further developed self-replicating property.

4) Replication is fundamental property of living forms.

F) Formation of first cell:

1) The nucleic acid present in protobionts cells was having capacity of self-duplication.

2) After wards it, started regulation different reactions specially protein synthesis.

3) The led, foundation of transformation of procells into a cell.

The entire process further resulted in biological evolution.

G) Biological evolution:

1) The first cell were marine with heterotrophic mode of nutrition, deriving food from surroundings.

2) Growth and multiplication of these cells depleted food arid resulted in the release of CO2 due to fermentation.

3) This further resulted in mutation and developed chromophores; which were having ability to trap sunlight. The light energy trapped was converted into chemical energy.

4) The entire process helped to transform heterotrophs into autotrophs, indicating on set of photosynthesis.

5) Finally due to release of oxygen as a byproduct of photosynthesis the reducing atmosphere of the earth changed into oxidizing atmosphere.

Q. 19: What are the first chemicals formed on earth surface?

Ans. First chemicals formed on the earth surface were water, ammonia. Methane etc.

Q. 20: Which is the land mark step in the process of origin of life?

Ans.: Formation of protein molecules is the land mark step in the process of origin of life.

Q. 21: What are protoproteins?

Ans.: Polymerization of amino acids developed proteins which showed enzymatic reactions. These proteins are known as protoproteins.

 

Q. 22: Write a note on coacervates?

Ans. 1) it is formation of aggregates of molecules or polymerization.

2) Oparin stated that large amount of proteins if shaken with polysaccharides it results in the formation of   coacervates.

3) These aggregates are mainly composed of some amount of water and proteins with polysaccharides in abundance.

4) Oparin’s coacervates also followed simple metabolism theory of operin.

5) Due to absence of lipid membranes these coacervates cannot replicate.

6) The other type of protobionts is microsphere.

7) Thus, oparin suggested that they might are originated from the primitive earth.

Q. 23: Describe microsphere theory of Sydney fox?

Ans.: 1) Sydney Fox (1959) after studying coacervates prebiotic atmosphere in laboratory.

2) He heated amino acids which polymerized into portends which are similar to proteins.

3) These aggregated into spherical colloidal droplets called microspheres.

4) Thus, it can be concluded that microspheres are fore runners of life form on earth.