D.1 origin-of-life-on-earth

ORIGIN OF LIFE ON EARTH

Option D.112 IB Biology 2011

Miss Werba

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THINGS TO COVER

• The conditions of pre-biotic Earth• Experiments of Miller and Urey• Hypothesis regarding first catalysts• Theory that regarding RNA and replication• Possible origin of membranes and prokaryotic

cells• Endosymbiotic theory for the origin

of eukaryotes

MISS J WERBA – IB BIOLOGY

THE SPONTANEOUS ORIGIN OF

LIFE

THE SPONTANEOUS ORIGIN OF LIFE ON EARTH

• There are 4 processes that were needed for the spontaneous generation of life on Earth:

– Non-living synthesis of simple organic molecules

– Assembly of these molecules into polymers

– Inheritance possible once self-replicating molecules originated

– Packaging of these molecules into membranes

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NON-LIVING SYNTHESIS OF SIMPLE ORGANIC

MOLECULES

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SYNTHESIS OF ORGANIC MOLECULES

• 15 billion years after the “Big Bang”, the planets began to form.

• The atmosphere on Earth at this time probably contained a variety of inorganic molecules:– Water vapour– Methane– Ammonia– Hydrogen– Carbon dioxide

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• The energy for forming the organic molecules was provided by:– frequent thunder storms and lightning strikes– volcanic activity– meteorite bombardment– high temperatures due to

greenhouse gases – UV radiation

(no ozone so was extreme)


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• These elements and inorganic molecules are presumed to have been sufficient for life to begin.

• The organic molecules may have been generated on Earth or introduced from space.


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• The hypothesis that life on Earth originated by introduction of complex organic chemicals or even bacteria via comets is called panspermia.

• A shower of comets about 4 thousand million years ago could have introduced complex organic molecules and water to the Earth and initiated chemical evolution.


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ASSEMBLY OF POLYMERS FROM ORGANIC

MOLECULES

ASSEMBLY OF POLYMERS

• There was little to no oxygen in the atmosphere at the time, as any oxygen was absorbed by rocks.

• This meant that there was no oxygen to steal electrons away from other atoms (ie. oxidise them).

• This would have resulted in a ‘reducing atmosphere’ which would have made the joining of simple molecules to form more complex ones more likely.


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• Experiments have shown that it is possible to form organic molecules in a reducing atmosphere

• However it is very difficult to do when there is oxygen in the atmosphere

• This polymerisation process would allow the larger chemicals needed by cells to form.


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• How were polymers — the basis of life itself —assembled????

• In solution, hydrolysis of a growing polymer would soon limit the size it could reach.

• This has led to a theory that early polymers were assembled on solid, mineral surfaces that protected them from degradation.

• In lab experiments they have been synthesized on clay.


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FORMATION OF SELF-REPLICATING

MOLECULES ALLOWS FOR INHERITANCE

SELF-REPLICATING MOLECULES

• In current cells, DNA can replicate but it needs the help of enzymes (proteins) to do this.

• The proteins are assembled based on information carried on the DNA and transcribed into RNA.

• So what came first.....the DNA to make proteins orthe proteins to make the DNA?!?!?!?!?


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• The synthesis of DNA and RNA requires proteins. • So:– proteins cannot be made without nucleic acids

and – nucleic acids cannot be made without proteins

• Wrong!


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• The synthesis of nucleotides and their bases could have happened easily.

• Once this had occurred, it is not hard to see how a single strand of RNA could have formed.

• Once this had occurred, complementary base pairing could have resulted in the non-enzymatic replication of RNA.


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SOURCE: Purcell, D. (2009)


• Self-replicating molecules are molecules that are able to undergo replication.

• They are able to act as a template for copies of themselves to be made.

• The only biological molecules capable of self-replication are DNA & RNA.

• Unlike DNA, RNA sequences are capable of self-replication: it can catalyse its formation from nucleotides in the absence of proteins.


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• The discovery that certain RNA molecules have enzymatic activity provides a possible solution.

• These RNA molecules — called ribozymes— incorporate both the features required of life:– storage of information – the ability to act as catalysts

• Active ribozymes can be easily assembled from shorter olignonucleotides (strands of nucleotides).


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• Ribozymes have been synthesized in the laboratory and can catalyze exact complements of themselves.

• The ribozyme serves as both:– the template on which short lengths of RNA

("oligonucleotides“) are assembled, following the rules of base pairing and

– the catalyst for covalently linking these oligonucleotides.


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• Evidence for this ideas is provided by the fact that many of the cofactors that play so many roles in life are based on ribose:

ATP NADFAD

coenzyme A cyclic AMP

GTP25MISS J WERBA – IB BIOLOGY

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PACKAGING OF SELF-REPLICATING MOLECULES

INTO MEMBRANES

FORMATION OF THE MEMBRANE

• The development of the lipid bilayer was imitated in the laboratory by Fox and his co-workers

• They heated amino acids without water and produced long protein chains

• When water was added and the mixture cooled, small stable microspheres or coacervates were formed


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• The coacervates seemed to be able to accumulate certain compounds inside them so that they became more concentrated than outside

• They also attracted lipids and formed a lipid-protein layer around them


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• If we assume that the coacervates also combined with self-replicating molecules such as RNA, we are looking at a very primitive organism...

• This is thought to have happened about 3.8 billion years ago


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• The aggregates or coacervates are also known as protobionts or proto cells.

• The most successful liposomes (protobiont in presence of lipids) at surviving would have passed on their characteristics and developed into early prokaryotes!


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SOURCE: McFadden, G. (2009)



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MILLER& UREY

EXPERIMENTS OF MILLER & UREY (1953)

• Stanley Miller and Harold Urey worked on trying to confirm some of these ideas regarding pre-biotic Earth.

• In 1953, Miller set up an apparatus to simulate conditions on the early Earth.

• The apparatus contained a warmed flask of water simulating the primeval sea and an atmosphere of water, hydrogen gas, CH4 (methane), and NH3 (ammonia).

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GO HERE !!!

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http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_miller-urey_experiment.html


• Sparks were discharged in the synthetic atmosphere to mimic lightning.

• Water was boiled, while a condenser cooled the atmosphere, raining water and any dissolved compounds back to the miniature sea.

• The simulated environment produced many types of amino acids and other organic molecules leading them to conclude the pre-biotic synthesis of organic molecules was possible.

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http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_miller-urey_experiment.html


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• This spontaneous generation of organic molecules was supported by investigation of meteorites.

• In 1970, a meteorite was found to contain 7 different amino acids, 2 of which are not found in living things on Earth.

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CONTRIBUTION OF PROKARYOTES


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MISS J WERBA – IB BIOLOGY SOURCE: McFadden, G. (2009)


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• Prokaryotes had the planet to themselves for about 2 billion years!

• Oxygen began to gradually accumulate in the atmosphere on Earth.

• Bacteria evolved naturally to contain a form of chlorophyll, which then allowed a simple form of photosynthesis to occur.

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• This caused an explosive rise in the levels of atmospheric oxygen known as the oxygen catastrophe.

• This had an irreversible effect on the subsequent evolution of life.

• The remaining chemicals in the “chemical soup” in the oceans were broken down into carbon dioxide and oxidised sediments.

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• In addition, a layer of ozone (O3) began to form in the upper atmosphere.

• This protected the planet from UV radiation from the Sun and blocked the production of new organic chemicals in the “chemical soup”.

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ENDOSYMBIOSIS

ENDOSYMBIOSIS

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ENDOSYMBIOSIS

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ENDOSYMBIOSIS

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ENDOSYMBIOSIS

• Grypania is ~2mm in diameter, so it is too big to be a prokaryotic cell.

• Tappania is definitely too big and complicated to be prokaryotic.

• Bangiomorpha had 3D structure! Definitely too complicated to be prokaryotic!

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ENDOSYMBIOSIS

• The oldest fossils of eukaryotic cells have been found to be approximately 1.5 billion years old.

• The endosymbiotic theory from Lyn Margulis (1967) tries to explain how eukaryotic cells may have evolved.

• Endosymbiosis: the condition in which one organism lives inside the cell of another organism

• Both cells benefit from this - the cells no longer can live separately from each other

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GO HERE !!!

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http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter26/animation_-_endosymbiosis.html

ENDOSYMBIOSIS

• Mitochondria and chloroplasts were once free living bacteria cells:

– Mitochondria aerobic bacteria

– Chloroplasts photosynthetic bacteria

• These cells were “swallowed up” by other cells by endocytosis cells engulfed but not eaten

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ENDOSYMBIOSIS

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ENDOSYMBIOSIS

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ENDOSYMBIOSIS

• Mitochondria:– additional energy (aerobic respiration) and

receives protection

• Chloroplast:– provide food by photosynthesis and receives

protection

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ENDOSYMBIOSIS

• Prokaryotes are similar to mitochondria and chloroplasts:– Similar size– Similar ribosomes (70S)– Contain DNA that is different from the nucleus– Surrounded by double membrane– Formation of new organelles resembles binary

fission

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ENDOSYMBIOSIS

• The four eukaryotic kingdoms are:– Protoctista– Fungi– Plantae– Animalia

• Eukaryotic cells have some advantages over prokaryotic cells so the early eukaryotes survived and proliferated

• Hence the wide diversity of species we know today!59

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D.1 origin-of-life-on-earth

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