B.tech biotech i bls u 1.2 theories of origin of life

Origin of Life

Course: B.Tech Biotech

Subject: Basic of Life Science

Unit: I

ORIGIN OF EARTH

The earth is presumed to have originated either planetesimal hypothesis and nebular hypothesis.

Origin of the UniverseThe universe began about 14.4 billion years ago

The Big Bang Theory states that, in the beginning, the universe was all in one place

All of its matter and energy were squished into an infinitely small point, a singularity

Then it exploded

The tremendous amount of material blown out by the explosion eventually formed the stars and galaxies

After about 10 billion years, our solar system began to form.

1.

Gradual condensation of interstellar dust from which our entire solar system is presumed to be formed.

The Nebular Hypothesis

2.

Earth is ~ 4,570,000,000 years old

The Age of the Earth

Meteorites give us access to debris left over from the formation of the solar systemWe can date meteorites using radioactive isotopes and their decay products

THEORIES OF ORIGIN OF LIFE

Several attempts have been made from time to time to explain the origin of life on earth.

As a result, there are several theories which offer their own explanation on the possible mechanism of origin of life.

Following are some of them:

1. THEORY OF SPECIAL CREATION

All the different forms of life that occur today on planet earth : created by super natural power.

This idea is found in the ancient scriptures of almost every religion.

Hindu mythology : Lord Brahma, the God of Creation,

Christian : God created this universe, plants, animals and human beings in about six natural days.

Sikh mythology : all forms of life including human beings came into being with a single word of God.

Special creation theory believes that the things have not undergone any significant change since their creation.

The theory of Special Creation was purely a religious concept, acceptable only on the basis of faith.

It has no scientific basis.

2. COSMOZOIC THEORY (THEORY OF PANSPERMIA

According to this theory, life has reached this planet Earth from other heavenly bodies(plnet or stars) such as meteorites, in the form of highly resistance spores of some organisms.

Highly resistant spores : lead to life on earth, named as “cosmozoa”.

This idea was proposed by Richter in 1865 and supported by Arrhenius (1908) and other contemporary scientists.

This theory lacks evidence, hence it was discarded.

3. THEORY OF CATASTROPHISM

modification of the theory of Special Creation.

It states that there have been several creations of life by God, each preceded by a catastrophe resulting from some kind of geological disturbance.

According to this theory, since each catastrophe completely destroyed the existing life, each new creation consisted of life form different from that of previous ones.

4. THEORY OF SPONTANEOUS GENERATION/ABIOGENESIS

Living organisms could arise suddenly and spontaneously from any kind of non-living matter.

One of the firm believers in spontaneous generation was Aristotle, the Greek philosopher.

Dead leaves falling from a tree into a pond would transform into fishes and those falling on soil would transform into worms and insects.

Some insects develop from morning dew and rotting manure.

Egyptians believed that mud of the Nile river could spontaneously give rise to many forms of life.

Thales (624-548 BC) suggested that oceanic water was the mother from which all living forms originated.

According to Empedocles life originated by itself from non living matter and imperfect forms were replaced by perfect forms.

Aristotle (384-322 BC) proposed that living forms are animated forms of non-living matter. He further stated that the vital forces operate constantly and improve the living world.

In the 17th century the idea of abiogenesis was opposed by an Italian physician Francisco Redi (1621-1697). For the first time he proposed through experiments, that life could arise only from pre-existing living things.

Experiment: sealing meat inside four closed flask, while leaving another four meat filled flasks open. Soon the meat in the open flasks was full of maggots.

Flies were entering and leaving the flask. Even after many days no worm appeared in the closed and sealed flask. This experiment confirmed his idea that new life can come only from early life.

14.2 The Origin of Life

Origins: Early Ideas

The History of Life

Spontaneous generation is the idea that life arises from nonlife.

Francesco Redi, an Italian scientist, tested the idea that flies arose spontaneously from rotting meat.

Chapter 14

3.

The theory of biogenesis states that only living organisms can produce other living organisms.

The History of Life

Louis Pasteur designed an experiment to show that biogenesis was true even for Microorganisms.

5. Theory of Biogenesis

Chapter 14

4.

Origins: Modern Ideas

Biochemical origin of life

Simple organic molecule formation

The primordial soup hypothesis was an early hypothesis about the origin of life.

Organic molecules could have been synthesized from simple reactions.

UV light from the Sun and electric discharge in lightning might have been the primary energy sources.

Modern Hypothesis of origin of Life

Chapter 14

Stanley Miller and Harold Urey were the first to show that simple organic molecules could be made from inorganic compounds.

The History of Life

Later, scientists found that hydrogen cyanide could be formed from even simpler molecules in simulated early Earth environments.

14.2 The Origin of Life

Chapter 14

5.

THE ORIGIN OF LIFE Origin of life is NOT an event Origin of life is a continuous process Stages

inorganic production of key simple organic moleculesproduction of more complex molecules that can synthesize

more of the same moleculedevelopment of a genetic code of self-replicating

molecules (RNA,DNA,proteins)production of the first cell by separation of these codes

from the outer world by a membrane Ocean environment by 4.0 by- fossils evident at

3.8by

THE ORIGIN OF LIFE Many complex organic molecules must have formed

before an organism produced

This process cannot occur on Earth today because the simple organism would be destroyed by oxidation or predation.

STEPS IN THE ORIGIN OF LIFE Aerobic vs. Anaerobic

oxygen poisons living cells so early life was anaerobic

Lack of free Oxygen >> No Ozone layer UV radiation kills cells so life had to originate at depth Water depths of 10m or more

Models non-oxidizing secondary atmosphere rich in the constituent

chemicals for life--H2O, CO2, N Energy in the form of UV radiation & Hot springs

STEPS IN ORIGIN OF LIFE Before the first cell>>Chemical Evolution

production of significant molecules necessary for life Phosphoric acid -can bond molecules and promote

long chain molecule formation Amino acids formed first since they do not form if

oxygen presentprobably formed on clay surfaces since they are attractive

and absorptive, also protection from UV Larger Molecules

amino acids are linked together by dehydration synthesis (water loss), clays have potential to absorb water, thus amino acids could be linked on clay surfaces

EXPERIMENTAL STUDIES A. I. Oparin- 1930s

Produced sugars and fatty acids from the constituents of an early atmosphere

Urey and Miller- 1953Production of cyanide, formaldehyde and 4 different

amino acids from water vapor, methane, hydrogen and ammonia and electrical sparks

Subsequent ExperimentsProduction of 18 of the 20 known amino acids and

extremely simple forms of DNA from gases rich in water vapor, CO2, and nitrogen and UV radiation

S.W. Fox (1959) produced protein-like (protenoids) chains from a mixture of 18 amino acids at 70oC in the presence of phosphoric acid

THE ENVIRONMENT FOR LIFE Volcanic Hot Springs Oceanic hydrothermal

vent system Deep (below the level of

UV penetration) Clays and/or Zeolites as

templates Similarity with present

day chemosynthetic heterotrophic organisms

THE FIRST CELLS All cells use the same genetic code Archaeobacteria- most primitive

Heterotrophs: obtain energy from surroundings by some chemical reaction

Obtain energy by converting CO2 and H2 to CH4 or by the reduction of sulfur compounds

Eubacteria10 Phyla, including cyanobacteria (Autotrophs:

manufacture their own food source) First Cells poorly developed metabolic systems

absorbed nutrients directly fermentation

LIFE Prokaryota

Appear 3.8-3.6 by no nucleus single loop chromosome with all genes reproduction-binary fission

Eukaryota Single cell appear 2 by Multicellular appear as trace fossils 1by and as body fossils

700my Nucleus with 2 pairs of chromosomes (2 copies of all genes) Asexual and SEXUAL reproduction>> more combinations

HOW DID LIFE ORIGINATE?

Living things (even ancient organisms like bacteria) are enormously complex.

Instead life almost certainly originated in a series of small steps, each building upon the complexity that evolved previously:

1. Simple organic molecules were formed.

Simple organic molecules (nucleotide)- the building blocks of life.

Experiments suggest that organic molecules could have been synthesized in the atmosphere of early Earth and rained down into the oceans. 

RNA and DNA molecules — the genetic material for all life — are just long chains of simple nucleotides.

2. Replicating molecules evolved and began to undergo natural selection.All living things reproduce, copying their genetic material and passing it on to their offspring.

Thus, the ability to copy the molecules that encode genetic information is a key step in the origin of life — without it, life could not exist.

This ability probably first evolved in the form of an RNA self-replicator — an RNA molecule that could copy itself.

Many biologists hypothesize that this step led to an "RNA world" in which RNA did many jobs, storing genetic information, copying itself, and performing basic metabolic functions.

Today, these jobs are performed by many different sorts of molecules (DNA, RNA, and proteins, mostly), but in the RNA world, RNA did it all.

3. Replicating molecules became enclosed within a cell membrane.The evolution of a membrane surrounding the genetic material provided two huge advantages: the products of the genetic material could be kept close by and the internal environment of this proto-cell could be different than the external environment.

4. Some cells began to evolve modern metabolic processes and out-competed those with older forms of metabolism.

everything changed when some cell or group of cells evolved to use different types of molecules for different functions: DNA (which is more stable than RNA) became the genetic material, proteins (which are often more efficient promoters of chemical reactions than RNA) became responsible for basic metabolic reactions in the cell, and RNA was demoted to the role of messenger, carrying information from the DNA to protein-building centers in the cell.

Cells incorporating these innovations would have easily out-competed "old-fashioned" cells with RNA-based metabolisms, hailing the end of the RNA world.

5. Multicellularity evolved.

As early as two billion years ago, some cells stopped going their separate ways after replicating and evolved specialized functions.

They gave rise to Earth's first lineage of multicellular organisms, such as the 1.2 billion year old fossilized red algae.

BOOK AND WEB REFERENCES

Book Name : 12th Std NCERT

http://en.wikipedia.org/wiki/Abiogenesis http://www.livescience.com/13363-7-theories-

origin-life.html http://education-portal.com/academy/lesson/the-

origin-of-life-on-earth-theories-and-explanations.html

IMAGES REFERENCES

1.http://d2hh5u5wjpwmol.cloudfront.net/wp-content/uploads/2011/03/universe.jpg

2.http://upload.wikimedia.org/wikipedia/commons/4/48/Planet_formation.jpg

3.http://bekarice.com/wpcontent/uploads/2014/07/spontaneous-generation.jpg

4.https://encryptedtbn1.gstatic.com/images?q=tbn:ANd9GcR1b_XWavXhz_GyL64OOa3ylkawCKXVta2rctLCcA_zxHa_UhRF

5.http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Miller.gif