Mythological approach......

Theory of Special Creation......

Spanish monk Father Suarez

19th century, life originated by supernatural powers/at successive intervals

Biblical concept, Father Suarez

Creation by God in 6 days

Man on 6th day & woman 7th day (12th rib of man)

Hindu mythology, Brahma (creator) Gods, men & devils (Head) Birds (Chest) Goats (Mouth) Plants (Hairs of body)

Ancient & medieval beliefs......

1. Cosmozoic Theory...... Life distributed through cosmos, resistant spores (cosmozoa) Reached earth accidentally from other planets Got favorable conditions Developed into living entities

Theory, Richter, 1865 supported by Arrhenius & others Living matter fail to survive extreme cold/dryness/intense irradiation Fails (how life originated & how spores reached earth)

Objections

Richter

Arrhenius

Support Fossils of micro-organisms in meteorites (1961) Space research, bacteria can withstand rigors of space travel & can survive in airless & waterless environment

2. Theory of Directed Panspermia......

Recently revived Civilization, advanced stages Decided to live on other planets Infected earth with microbes (Directed Panspermia)

Nobel Laureate Francis Crick & Leslie Orgel

3. Theory of Spontaneous Generation/Abiogenesis......

Till 17th century people believed on abiogenesis Epicurus, ancient Greece, worms & other animals developed from soil by action of moisture & warmth of sun & air Aristotle, living things arose spontaneously

Worms, bee larvae, wasps, ticks developed from dew, rotten slime, manure etc. Eels (sea mud) Frogs, salamanders (Coagulated slime) Newton,Descrates, supporter

Newton

Descrates

4. Theory of Biogenesis.........

a.Redi’s Experiment.......... Italian physician, simple experiment, no abiogenesis

Cooked few meat pieces, placed them in 3 jars (A, B, C)

Jar C left uncovered

Jar B covered with fine muslin cloth A was covered with parchment paper After few days, maggots appeared in jar C not in A & B Flies seen sitting & laying eggs in jar B

No maggots in jar B He concluded flies arose from eggs laid by parent flies Maggots cannot appear spontaneously

b. spallanzani’s Experiment.......

Also proved no abiogenesis He sealed neck of flasks with infusions so that air cannot enter inside Boiled infusion for 4 hours Left for many days

Found no living organisms appeared even after long time Concluded micro-organisms develop only when get favorable conditions

c. pasteuR’s Experiment........ Remaining doubts cleared Kept a mixture of sugar & yeast powder in a flask, filled half of it with water Softened neck of flask, drew into ‘S’ shape Boiled till steam observed Louis Pasteur

Flask was cooled Noticed that contents remained unchanged after many days When neck was cut-off, solution developed organisms Concluded air has microbes, reached solution & grew

Experiment revealed life do not arise spontaneously under present day conditions Conditions on earth billion years ago different from present First form of life might descended spontaneously from chemical substances

Modern hypothesis Or

Biochemical origin of life

Most primitive organisms generated spontaneously at some time from inorganic matter & physical forces came into action Haeckel

Haldane Oparin Miller Urey

Supported Oparin formulated biochemical origin of life sequentially

A.Origin of earth & its primitive atmosphere........

Believed to be 6 million years old

Either a broken/molten part of sun or gradual condensed interstellar dust

Solar system originated from this

Initially a spinning fiery ball of hot gases & vapors or various elements

Hundreds of millions years after, gases condensed into molten core

Elements stratified (density)

Iron & Nickel sank (core of earth)

Lighter elements (silicon, aluminium) (shell)

Helium, hydrogen, oxygen, nitrogen & carbon (gaseous atmosphere Originated temperature was 5000-6000ºC Geologists believe didn’t rose above 9000ºC Hydrogen, oxygen, carbon & nitrogen (not freely existing)

Hydrogen combined with oxygen (water) Ammonia, methane & cynamide Temperature so high (gaseous form) Water (superheated steam) Primitive atmosphere As earth cooled gradually some gases liquefied

Combined with metals to form oxides, carbides & nitrides Carbon as dicarbon, cyanogen, methane, carbon dioxide, carbon monoxide & metal carbide Nitrogen existed as nitrides Oxygen formed oxides

Liquefied turned into solids Steamed condensed into water (rain) Rain droplets reached superheated earth crust, evaporated & reached back to atmosphere Cycle continued millions for millions of years

Cooling of earth surface Became sufficient enough to hold water & large water bodies First oceans formed Oceanic water (atmospheric ammonia, methane) Mineral rocks dissolved, minerals, salts accumulated (oceanic water)

Primitive oceans (pH-8) 3 billion years ago, earth solid crust (molten rocks & hot boiling sea water) Sea water dissolved ammonia, methane, some minerals & salts

Primitive atmosphere devoid of free oxygen, rich in ammonia, methane, hydrogen Earth bombarded with high energy radiation (sun)

b. Chemical origin of Life (Chemogeny)......

Oparin suggested, from simple compounds more complex organic compounds formed Gradually under influence of electric charges, UV-rays/corpuscular radiations

1.Origin of organic compounds......

a.Formation of hydrocarbons........

When temperature cooled down to 1000ºC

Simple, saturated & unsaturated hydrocarbons formed

Combination of highly reactive free radicals (CH and CH2) Metal carbides reacted with steam

b. Formation of oxy & hydroxy derivatives of hydrocarbons......

Saturated & unsaturated hydrocarbons reacted with superheated steam Oxy & hydroxy derivatives (aldehydes, ketones & acids) formed

Carbon monoxide reacted with water (formic acid)

Due to its reactivity CO, resulted in formation of prebiotic compounds

c. Formation of carbohydrates......

Small chain compounds of C, H & O formed from hydroxy derivatives 1st formed compounds (glucose & fructose) Condensation resulted in formation of di & polysaccharides (Starch)

d. Formation of fatty acids & glycerol........

Condensation, polymerization (aldehydes & ketones) oxidation Less percent of oxygen, long chained carbon Glycerol & fatty acids formed fats

e. Formation of amino acids........

Combinations of hydrocarbons, ammonia & water under influence of freely available energy Amino acids formed

Hot dilute soup.......

Synthesis of carbohydrates, fats, amino acids & complex organic substances (sea) Hot dilute soup (Haldane) Organic molecules can not accumulate today Microbes use & degrade them as food

On primitive earth, microbes absent, molecules persisted Thermodynamics, such molecules cannot accumulate in solution in large numbers, break fast Accumulated in layers on mud, surface for reactions

2. Formation of complex organic molecules......

Hot dilute soup, simple organic substances collided, reacted & aggregated New complex molecules Polysaccharides, fats, proteins, purines, pyrimidines, nucleosides & nucleotides (Polymerization)

Sugar molecules (starch, cellulose & glycogen) Fats (glycerol) Amino acids (polypeptide chains) Acted as primitive enzymes Protein formation (Landmark in origin of life)

Proteinoids......

High temperature, UV-light, electric discharge & atomic radiations (decomposition of proteins) Proteins hydrolysed to monomers in aquatic medium

Heating a mixture of several amino acids at low temperature, polymerization of amino acids (polypeptide chain) Thermal proteinoids Resemble natural proteins Bacteria use them in culture medium (enzymatically)

Microspheres.........

Molecular aggregates of protenoids Resemble spherical bacteria Easily formed when water added to thermal proteinoids Uniform shape & size

Resemble coccoid bacteria, tend to form long chains (streptococci) Considerable stable Electron micrograph (double layered) Gram positive & negative forms

Non-random motility Information could communicate Hypotonic solution (swell) Hypertonic solution (shrink) Osmosis

Retain enzyme-like activities Binary fission/budding Excellent model for protocells Originated (proteinoids) Structural & functional attributes of contemporary cells

3. Coacervates.........

Oparin & Sydney Fox, large sized molecules synthesized abiotically on primitive earth (colloidal aggregates due to intermolecular attraction) Coacervates

Solutions of oppositely charged colloids mixed (coacervate droplets) Higher concentration of organic polymers than in aqueous phase Open systems If enzyme & monomer added (polymers)

Large enough to be seen (microscope) Remind of bacteria/unicellular organisms Lipid molecules joined (outer layer) Represents lipid membrane

Represented protocell model Absorb proteins & other materials from surroundings Grow in size & complexity Budding like bacteria

Poor models of protocells Formed from a mixture of contemporary bioproteins Unstable & disintegrate with time

3. Formation of nucleic acids (Naked Genes).......

Self replicating polynucleotides formed in primordial earth (3.5 billion years ago) Errors during replication, different types of nucleic acids formed

Certain polynucleotides developed quality of directing synthesis of polypeptides RNA guided protein synthesis in present animals suggest RNA, 1st carrier of genetic information

Genetic code & translation of nucleotide sequences into amino acid sequences, established very early stage of organic evolution Nucleic acid (naked genes)

(i)Protoribosomes........

Nucleoproteinoid particles, fibrous/globular

Model for early ribosomes

4. Formation of nucleoproteins or protobionts............

Due to aggregation, giant molecules of nucleoproteins formed by union of nucleic acid & proteinoid molecules

(ii) Protoviruses.......

Giant nucleoproteinoid molecules, free living gene Compared with present day viruses (nucleic acid core & protein covering) Protobionts by Oparin

Biological Evolution (Biogeny)

5. Formation of primary organisms (Ecobionts).......

Macromolecules aggregate (Coacervates) Contained proteins, nucleoproteins & other organic molecules (various combinations)

Polarized films of phospholipids (surface membrane of coacervates) Appeared as soap-like Surface membrane= plasma membrane Aggregation of self-replicating RNA or DNA & protein molecules

Oparin said, coacervates (hot dilute soup), isolated by formation of polarized membrane of phospholoipids Nucleoproteins developed into first living cells

Evolution of modes of nutritions

1.Chemoheterotrophs......

First living organisms

Obtained energy by fermentation of complex organic substances available from sea broth

Multiplied rapidly in dissolved nutrients Nutrients began to disappear, gradually exhausted Evolution of other modes of nutritions

a.Parasitism......

Some started living inside bodies of living cells & obtained food Parasites Monerans, viruses & few protists

b. Saprophytism.......

Some started withdrawing nourishment from bodies of dead & decaying cells Bacterial groups

c.Predator or animalism........

Animal-like way of eating 1 animals eats other (whole/part)

d. Chemosynthesizers or chemoautotrphs.......

Protocells with enzymes of metabolic pathways use less complex nutrients & synthesized more complex molecules Obtained energy by fermentation

Similar to anaerobic bacteria/yeast Released large amount of carbon dioxide in atmosphere Fore-runners of photosynthetic cells

e. Anaerobic photoautotrophs........

Evolution of chlorophyll (photocells to utilize solar energy & form carbohydrates) Photosynthetic cells 1st were anaerobic Didn’t used water & release oxygen

Similar to present day sulfur bacteria Cleaved hydrogen sulfide to hydrogen & sulfur Hydrogen used in organic synthesis Sulfur released as waste product (similar to aerobic autotrophs)

Beginning of autotrophism Energy released by anaerobic respiration/fermentation Chemosynthesis (chemosynthesizers)

f. Aerobic photoautotrophs.......

It is presumed, accumulation of CO2, formation of cholorophyll (evolution of autotrophs) Cyanobacteria-like Use water as hydrogen source Carbon dioxide as carbon source

Released free oxygen in atmosphere (oxygen-producing photosynthesizers) 3300-3500 million years ago

7. Oxygen revolution & present day atmosphere......

Increase of photoautotrophs, oxygen liberated Free oxygen reacted with methane & ammonia (CO2 & N2) Modern atmosphere

Oxygen accumulated 2 billion years ago First eukaryotes Aerobic mode of respiration

Cognogeny

8. Evolution of eukaryotes......

Protocells (prokaryotic & archaebacteria-like) Eukaryotic cells evolved from archaic prokaryotic cells 2 views

1.Symbiotic origin..........

Lynn Margulis, Boston University

Some anaerobic predator host cells engulfed primitive aerobic bacteria, failed to digest them

Oxygen respiring bacteria established inside host cells

Developed mutual association (1st eukaryotic cells) Predator cells became first plant cells Aerobic bacteria established as mitochondria Blue green algae as chloroplasts

2. Origin by invagination......

Organelles of eukaryotic cells might have evolved by evagination of surface membrane of prokaryotic cell

3. Cognogeny........

Involves diversification in Protozoa, Metazoa & Metaphyta Evolution of 1st plants included photosynthesis both in Protista & Monera due to exhaustion of food supply

Experimental evidences in support of biochemical origin of life.........

Modern theory based on certain evidences collected from spectroscopic analysis of light coming from sun & other planets Also from experiments conducted in artificial environments

Experimental synthesis of organic compounds.......

Stanley Miller & Stanford Urey (University of Chicago) Successfully created conditions (past)* Formed amino acids (glycine & alanine & complex compounds) in vitro

Used water vapor, methane, ammonia & hydrogen gases in a closed chamber Exposed to electric discharge for few days Miller suggested that electric discharges produced violent storms during lightening

Formed amino acids & other complex organic compounds (components of living system) Accumulation of organic substances in soupy sea when living entities were absent

Modern concept further supported by viruses......

Intermediate between living & non-living Simplest organization Ultramicroscopic (100-300 mµ Crystallized like organic substances

Pass through filters & can multiply only within living cells Often called ‘Escaped Genes’ Have a central core of RNA/DNA Encased in a protein coat

When enters a living cell, protein coat lost, nucleic acid liberated in cytoplasm Protoplasm of infected cell produces numerous nucleic acid particles similar to that of virus Newly formed particles covered by protein coat

Present form of viruses cannot be considered as ultimate link because they can flourish only inside living cells They are not primitive If free-living virus existed must resemble first cell

Discovery of bacteriophages, mycoplasma, Rickettsiae & viroids also support.....

Bacteriophages (parasites of bacteria) Tadpole-like Head with DNA, protein coat, tail of protein

When bacteriophage attacks a bacterium, only DNA enters cell & protein coat cast off Whole structure now resembles hypodermic needle DNA synthesizes numerous copies, develops protein coat When bacterium dies particles liberated

Mycoplasma.....

Have both DNA & RNA granules encased by a membrane of proteins, fatty acids & cholesterol

Rickettsiae......

Resemble mycoplasma Represent another group of pathogens

Recently synthesis of a DNA molecule with 77 nucleotides in a test tube by Dr. Khorana further supports synthesis of genes by union of nucleotides in nature Awarded Noble Prize for cracking genetic code with Nirenberg & Holly (1970)

Where life originated?

Many simpler & lower animals are aquatic & marine Cells & body fluids of all animals contain salts suggesting life began in ocean

Many believe life originated in tidal zone rich in oxygen, CO2, light, minerals, most suitable for plant & animal growth Earliest remains (marine) Many invaded fresh water & land later

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