THE ORIGINS OF LIFE EARLY HYPOTHESIS SPONTANEOUS GENERATION (ABIOGENESIS) For thousand of years people believed that living organisms could arise spontaneously,

THE ORIGINS OF LIFE

EARLY HYPOTHESISSPONTANEOUS GENERATION

(ABIOGENESIS) For thousand of years people believed

that living organisms could arise spontaneously, or naturally,in a few days or week from non-living matter.This idea is called spontaneous generation. (abiogenesis)

ABIOGENESISNon-living matter living

in a certain time organisms

• IT IS BASED ON OBSERVATION AND INTUITION• Aristotle’s ideaExamples:

mud of Nile frogs sweat fleas garbage

mice decay meat flies

• Those things have active principle that are responsible for life.

EARLY EXPERIMENTS

• Jan Baptista van Helmont(1600s) performed an experiment to support the abiogenesis.

Wheat mice + after 21 dayssweaty man shirt• He reasoned that human sweat was the

active principle that changed wheat grains into mice.

• It is uncontrolled experiment.

• Francesco Redi(mid 1600s) performed an experiment against the spontaneous generation

• He was the first person to see that maggots develop into flies.

( fly eggs maggots pupas flies)

EARLY EXPERIMENTS

REDI’S EXPERIMENT

I. ExperimentOpen jar

Decaying meat

Meat was gone

A

Flies were

appeared

B

Sealed jar

No flies in jar

• The first experiment proved only that the meat had to be exposed to open air in order to develop maggots.

• It did not prove that the flies were the source of the maggots.

• Many scientists of the time claimed that fresh air was necessary for abiogenesis. They argued, Redi had prevented the needed air from reaching the meat.

REDI’S EXPERIMENT

II. Experiment

REDI’S EXPERIMENT

Gauze wire(allowed the fresh air)

Flies were appeared on nettig

No flies in jar

Flies were attracted by odor of rotting meat but they could not reach the meat

Spontaneous Generation of Microorganisms

Anton van Leeuwenhoek discovered microorganisms in a drop of water. He was found that when hay or soil was placed in sterile water, millions of microorganisms appeared within a few hours.

John Needham (1745) performed some experiments that reinforced the belief in the spontaneous generation of microorganisms

Spontaneous Generation of Microorganisms

•He boiled flasks of chicken, lamb, and corn broth for a few minutes to kill the microorganisms.

•He sealed the flask.

•After several days he opened and examined the flask and it was full of microorganisms.

Nutrient broth

Lorenzo Spallanzani (1765) challenged Needham’s conclusion.

• He boiled the flasks of chicken, lamb and corn broth much longer time.

• He obserbed no microorganisms in the flask.

Spontaneous Generation of Microorganisms

Nutrient broth

Spallanzani vs Needham: He had not heated the long

enough to kill all the organisms originally present.

Needham vs Spallanzani :He had destroyed the vital principle in the air that was needed to bring about the generation of new organisms.

Spontaneous Generation of Microorganisms

Disproving Spontaneous Generation

Louis Pasteur (1860) He tought that microorganisms and their spores were present in the air and that they became active and reproduced when they entered the nutrient broth.

He designed an experiment showed that developed in a nutrient broth came from spores and microorganisms in the air.

As long as the flasks were not disturbed, the content remained sterile. Microorganisms grew in the flasks only when the flasks were tipped and some broth ran into the neck and became contaminated.

ORIGINS OF LIFE

1. AUTOTROPH HYPOTHESIS• It is claimed that the first organism

on the earth was an autotroph.• Since autotrophs are very complex

and can synthesize their own food and food stuffs for other organisms, some scientists rejected the autotroph hypothesis saying that the first organism could not be so complex as to synthesize such foodstuffs.

ORIGINS OF LIFE

2. PANSPERMIA• According to some scientist, life reached the earth from other planets.• This hypothesis claimed that

spores and seeds from space initiated life on earth.

• It was not widely accepted because it did not explain the formation of the first organism in space.

ORIGINS OF LIFE

3. CREATION (Transcendental)• In spite of all these hypothesis, people remained unsatisfied.• Some people suggested that God created all living and non-living things.• This hypothesis cannot be tested or

disproved.

ORIGINS OF LIFE

4. HETEROTROPH HYPOTHESIS • assumes that heterotrophs evolved

from non-living material very slowly under a special set of environmental conditions.

• was developed by OPARIN• supported by Stanley Miller, Harold

Urey, and Sidney Fox.• does not contradict the theory of

evolution.

Sidney Fox

HETEROTROPH HYPOTHESIS

The Conditions of First Atmosphere• The gases of the first atmosphere

(Hydrogen, Water vapor,Ammonia,Methane)• Temperature was high.• Oceans were almost at boling point of

water.(hot thin soup)• Simple compounds in the atmosphere and

dissolved in the oceans could have reacted to form more complex organic compounds.These reactions require energy.

The Conditions of First Atmosphere

The sources of the energies are1. Heat given off by the earth2. Radiation from the decay of

radioactive elements in the Earth’s crust

3. Electrical energy from the lightning

4. X rays5. UV, visible light from sun

Natural Synthesis of Organic Compounds

• Under these conditions there would have been enough energy available for the breakdown and formation of chemical bonds. The first nucleotides, amino acids, and sugars could have been formed during this period .

• Stanley Miller and Harold Urey (1953) designed an experiment stimulating the conditions of the primitive earth.

Natural Synthesis of Organic Compounds

• The specially designed experimental apparatus contained four gases;Hydrogen, water vapour, ammonia,methane.

• Boiling water in the apparatus forced these gases to circulate past sparking electrodes.

• He ran experiment for a week.• He analyzed the content of the apparatus

and found that it contained urea, various amino acids, hydrogen cyanide, lactic acid and acetic acid.

AGGREGATES OF ORGANIC COMPOUNDS

WATER PROTEINSIMPLE

COACERVATES

COMPLEXCOACERVATES

developed

(evolution of)

1. Biochemical system with the capacity to release energy from the organic compound

2. Growth

3. Reproduction

Primitive living thing

Protein complexes develop into non-living structure having some of the characteristics of life

The photograph above shows Oparin’s coacervate droplets. Each droplet is a cluster of macromolecules surrounded by a shell of water in which the individual water molecules are rigidly oriented relative to the macromolecules. Such droplets have a tendency to selectively adsorb and incorporate various substances from the surrounding medium.

Sidney Fox’s proteinoid microspheres are formed by heating dry mixtures of amino acids to moderate temperatures, then cooling the mixture. The microspheres show many of the characteristics of living cells.

PROTEINOID MICROSPHERES, another kind of microspheroidal aggregate, studied by Sidney W. Fox of the University of Miami, forms from “thermal proteinoid,” a polymer produced by heating dry mixtures of amino acids to moderate temperatures. Under suitable conditions thermal proteinoid will form microspheres several micrometers in diameter, which grow slowly and eventually bud. The microspheres seem to have a two-layer membrane suggestive of that in bacteria.

Figure: Sidney Fox’s proteinoid microspheres can absorb materials from the environment, grow and divide in two by fission.

EVOLUTION OF ENERGY CONVERSION PROCESS

Primitive first living autotrophic organisms

Atmosphere organism -photosynthetic bacteria

(lack free oxygen) - anaerobic cellular (no oxygen released)

respiration - chemosynthetic bacteria

- heterotroph - other algae -cyanobacteria (use water, release

oxygen)

Evolution of aerobic

Cellular respirationUV

blocked

Xrays

Ozone layer

Evolution of terrestrial organism