THE ORIGINS OF LIFE EARLY HYPOTHESIS

SPONTANEOUS 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)

ABIOGENESIS

Non-living matter living

in a certain time organisms • IT IS BASED ON OBSERVATION AND INTUITION • Aristotle’s idea Examples: mud of Nile sweat garbage decay meat frogs fleas mice 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 days sweaty man shirt • He reasoned that human sweat was the active principle that changed wheat grains into mice.

• It is

uncontrolled experiment.

EARLY EXPERIMENTS

• 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)

B A

REDI’S EXPERIMENT I. Experiment

Open jar Flies were appeared Meat was gone Decaying meat Sealed jar No flies in jar

REDI’S EXPERIMENT

• 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

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

appeared within a few hours.

discovered microorganisms in a drop of water. He was found that when hay or soil was placed in sterile water, millions of microorganisms

Spontaneous Generation of Microorganisms John Needham

microorganisms

(1745)

performed some experiments that reinforced the belief in the spontaneous generation of

•He boiled flasks of chicken, lamb,

and corn broth for a few minutes to kill the microorganisms.

•He sealed the flask.

Nutrient broth

•After several days he opened and

examined the flask and it was full of microorganisms.

Spontaneous Generation of Microorganisms

Lorenzo Spallanzani

(1765) challenged Needham’s conclusion.

• He boiled the flasks of chicken, lamb and

corn broth flask.

much longer time .

• He obserbed no microorganisms in the

Nutrient broth

Spontaneous Generation of Microorganisms 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.

Disproving Spontaneous Generation

Louis Pasteur

(1860)

microorganisms and their spores were present in the air and that they became active and reproduced when they entered the nutrient broth.

He tought that 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 cl

aimed that spores and seeds from sp ace initiated life on earth.

• It was not widely

accepted because it did not explain the formation of the first organism in s pace .

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 are 1. Heat given off by the earth 2. Radiation from the decay of radioactive elements in the Earth’s crust 3. Electrical energy from the lightning 4. X rays 5. 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 PROTEIN SIMPLE COACERVATES Protein complexes develop into non-living structure having some of the characteristics of life Primitive living thing COMPLEX COACERVATES developed (evolution of)

1. Biochemical system with the capacity to release energy from the organic compound 2. Growth 3. Reproduction

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 Atmosphere

(lack free oxygen)

first living organism autotrophic organisms

-photosynthetic bacteria - anaerobic cellular (no oxygen released) respiration - chemosynthetic bacteria - heterotroph - other algae -cyanobacteria (use water, release oxygen)

Evolution of terrestrial organism Ozone layer UV Evolution of aerobic Cellular respiration