1.5. - the origin of cells
TRANSCRIPT
1.6. The origin of cells
Miltiadis-Spyridon Kitsos Platon IB Diploma
https://endosymbiotichypothesis.files.wordpress.com/2010/09/1471-2105-9-393-1-l.jpg
The official IB Diploma Biology guideEssential idea: There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today.
https://ibpublishing.ibo.org/server2/rest/app/tsm.xql?doc=d_4_biolo_gui_1402_1_e&part=8&chapter=1
Spontaneous generation is the formation of living organisms from non living matter
Ancient Greek Theophrastus c. 371 – c. 287 BC reported that Silphium had sprung out of soil without being planted before. An example of spontaneous generation?
Aristotle c. 384 – c. 322 BC wrote about insects being formed from the dew, or from the hair, flesh of faeces of animals.
How does passive observation affects our judgment? Why these ideas persisted for so many years?
Swiss botanist Paracelsus (1493-1541) believed in the spontaneous generation of mice, frogs and eels from decaying matter.
http://www.nndb.com/people/563/000107242/theophrastus-1-sized.jpg
http://www.missouriplants.com/Yellowopp/Silphium_integrifolium_plant.jpg
https://upload.wikimedia.org/wikipedia/commons/a/ae/Aristotle_Altemps_Inv8575.jpg
https://youtu.be/WNByRghR6sw
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Refutation of the theory of spontaneous generation
Francesco Redi (1626-1697) using a controlled experiment showed that maggots may not develop in pieces of meat not exposed to air
As our knowledge and understanding on microbiology and sexual reproduction improved more evidence accumulated showing the the theory of spontaneous generation was wrong
The era of active experimentation
Similarly Lazzaro Spallanzani demonstrated that organism may develop only in broths exposed to air.
https://upload.wikimedia.org/wikipedia/commons/a/af/Francesco_Redi,_founder_of_experimental_biology.jpg
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Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth.The swan-neck flasks experiments – experimental refutation of the theory of spontaneous generation
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Louis Pasteur (1822-1895), famous French scientist, known for his discoveries in the field of microbiology and immunology. He contacted a series of experiments that contributed to the final refutation of the theory of spontaneous generation.
1. Glass flasks were filled with nutrient broth.
2. Neck of flasks were bent using flame to form the so called swan necks. Broth was sterilized by boiling.
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Hypothesis: Life will not arise spontaneously in broths isolated from open air.
Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth.The swan-neck flasks experiments – experimental refutation of the theory of spontaneous generation
3. Swan neck flasks were left to sit undisturbed for several days. No signs of microbial growth were detected.
http://s.hswstatic.com/gif/scientific-method-9.jpg
http://amoebamike.wordpress.com/2009/10/06/spontaneous-generation-a-brief-history-of-disproving-it
4. In second treatment neck of flasks was broken. After several days broth was discolored and cloudy, indicating the development of bacteria.
http://amoebamike.wordpress.com/2009/10/06/spontaneous-generation-a-brief-history-of-disproving-it
Conclusion: Spontaneous generation is refuted since microbes may not grow spontaneously in isolated broths. A source of contamination is always needed.
Use the tutorials to learn about Pasteur’s experiment.
Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth.
http://bcs.whfreeman.com/thelifewire/content/chp03/0302003.html
Repeat Pasteur’s experiment and see the results for yourself.
http://biologyjunction.com/pasteur_experiment.htm
http://www.sumanasinc.com/webcontent/animations/content/scientificmethod.html
Slide from
According to the cell theory, every cell comes from a pre-existing cell
while eukaryotes undergo mitosis and, those that reproduce sexually, produce gametes via meiosisThus, there is a continuity of life from the ancestral cells to the existing cells
Male gamete
Female gamete
Fertilization and
Development of the zygote
Meiotic division and gamete formation
Mitotic divisions
Prokaryotic cells are divided through binary fission,
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There is not enough evidence to propose a natural mechanism on how cells may be produced by simpler subunits.
We also accept that cells come from pre-existing cells because..
There is no example of cell increase at any organizational level without cell division of pre-existing cells.
https://youtu.be/Q6ucKWIIFmg
We also accept that cells come from pre-existing cells because..
We also accept that cells come from pre-existing cells because..
Viruses are produced via the combination of simpler macromolecules but they are non-cellular structures
https://youtu.be/Rpj0emEGShQ
Origin of the first cellThe first cells must have arisen from non-living material
Lets step back into time…
Having traced the origin of the first cells back into time we still have a big question mark: How did the first cells arise?
Plausible hypotheses:(a) Cells have an extraterrestrial origin(b) First cells may have arisen from non living material
Here are some evidence supporting the idea that the complex structure of cells went througha series of evolutionary steps of increasing complexity.
Origin of the first cellThe first cells must have arisen from non-living material
The first atmosphere was formed by outgassing of gases trapped in the interior of the early Earth, a process which still goes on today through volcanic eruptions.
3.8 billion years ago the earth's atmosphere was a reducing mixture of nitrogen (N2), methane (CH4), water vapor (H2O), and possibly ammonia (NH3)
It is believed that solar radiation and lightning discharges into the reducing gas mixture produced natural organic compounds
Stage 1: Formation of important organic molecules
Origin of the first cellThe first cells must have arisen from non-living material
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The Miller-Urey experimentsThe first cells must have arisen from non-living material
Stanley Miller and Harold Urey contacted an experiment, that replicated the conditions in the primitive atmosphere. Water vapor passed through a mixture of methane (CH4), hydrogen and ammonia (NH3). Electrical discharges were used to simulate lightning.
The atmosphere was cooled and the vapor was condensed. Resulting water was checked for organic compounds. Different organic compounds (e.g., amino acids) were produced.
https://en.wikipedia.org/wiki/File:Miller-Urey_experiment_-_Work_by_the_C3BC_consortium,_licensed_under_CC-BY-3.0.webm
https://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Miller-Urey_experiment-en.svg/2000px-Miller-Urey_experiment-en.svg.png
The Miller-Urey experimentsThe first cells must have arisen from non-living material
Stanley Miller and Harold Urey developed a device which would replicate the conditions in the primitive atmosphere. Water vapor passed through a mixture of methane (CH4), hydrogen and ammonia (NH3). Electrical discharges were used to simulate lightning.
The atmosphere was cooled and the vapor was condensed. Resulting water was checked for organic compounds. Different organic compounds (e.g., amino acids) were produced.
https://en.wikipedia.org/wiki/File:Miller-Urey_experiment_-_Work_by_the_C3BC_consortium,_licensed_under_CC-BY-3.0.webm
https://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Miller-Urey_experiment-en.svg/2000px-Miller-Urey_experiment-en.svg.png
Conclusion: Vital organic molecules may had been produced
in the primitive atmosphere fro
m simpler m
olecules and
energy offered from lightning.
The first atmosphere was formed by outgassing of gases trapped in the interior of the early Earth, which still goes on today in volcanoes.
1.9 billion years ago the earth's atmosphere was a reducing mixture of nitrogen (N2), methane (CH4), water vapor (H2O), and possibly ammonia (NH3)
Solar radiation and lightning discharges into the reducing gas mixture are believed by the consensus of evolutionists to have produced natural organic compounds
Polymerization of carbon compoundsThe first cells must have arisen from non-living material
Deep sea vents: Areas in the deep sea floor where gushing hot water comes out along with reducing chemicals such as iron sulfate.
These chemical may have provided the energy for the assembly of simpler carbon compounds Into polymers.
https://youtu.be/rTR6gGDWcJk
Read more
Meet Luca, the Ancestor of All Living Thingshttp://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html?_r=0
We’ve been wrong about the origins of life for 90 yearshttp://qz.com/761430/weve-been-wrong-about-the-origins-of-life-for-90-years/
The first atmosphere was formed by outgassing of gases trapped in the interior of the early Earth, which still goes on today in volcanoes.
1.9 billion years ago the earth's atmosphere was a reducing mixture of nitrogen (N2), methane (CH4), water vapor (H2O), and possibly ammonia (NH3)
Solar radiation and lightning discharges into the reducing gas mixture are believed by the consensus of evolutionists to have produced natural organic compounds
Deep sea vents: Areas in the deep sea floor where gushing hot water comes out along with reducing chemicals such as iron sulfate.
These chemical may have provided the energy for the assembly of simpler carbon compounds Into polymers
https://youtu.be/rTR6gGDWcJk
Read more
Meet Luca, the Ancestor of All Living Thingshttp://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html?_r=0
We’ve been wrong about the origins of life for 90 yearshttp://qz.com/761430/weve-been-wrong-about-the-origins-of-life-for-90-years/
Conclusion: Reducing chemical released in hydrothermal vents
may have provided the energy for the polymeriza
tion of
carbon compounds .
Polymerization of carbon compoundsThe first cells must have arisen from non-living material
Remember what we discussed about phospholipid chemistry? Phospholipids are amphipathic molecules with a natural tendency to build bilayers. Experiments have demonstrated the ability of these phospholipid bilayers to form vesicles which then, may engulf and isolate other molecules.
The formation of membranes was a giant step in the evolution of the cells since it allowed the isolation of environments and internal chemistry.
Stage 3: Formation of membranesThe first cells must have arisen from non-living material
Read more
The early evolution of lipid membranes and the three domains of lifehttp://www.nature.com/nrmicro/journal/v10/n7/index.html
Jonathan Lombard, Purificación López-García and David Moreira, The early evolution of lipid membranes and the three domains of life, NATURE REVIEWS | MICROBIOLOGYVOLUME 10 | JULY 2012 | 507
Remember what we discussed about phospholipid chemistry? Phospholipids are amphipathic molecules with a natural tendency to build bilayers. Experiments have demonstrated the ability of these phospholipid bilayers to form vesicles which then, may engulf and isolate other molecules.
The formation of membranes was a giant step in the evolution of the cells since it allowed the isolation of environments and internal chemistry.
Stage 3: Formation of membranesThe first cells must have arisen from non-living material
Read more
The early evolution of lipid membranes and the three domains of lifehttp://www.nature.com/nrmicro/journal/v10/n7/index.html
Jonathan Lombard, Purificación López-García and David Moreira, The early evolution of lipid membranes and the three domains of life, NATURE REVIEWS | MICROBIOLOGYVOLUME 10 | JULY 2012 | 507
Conclusion: Amphipathic molecules may have formed the first
bilayers which soon formed ready-made vesicles enclosing
inheritance molecules and allowing internal chemistr
y.
RNA (ribonucleic acid) may have been the first genetic material since it has diverse properties.• May store information • Self-replication (non-enzymatic in certain cases) • Acts as a catalyst
Stage 4: Developing inheritanceThe first cells must have arisen from non-living material
http://biology-forums.com/gallery/195549_23_08_14_12_26_47.jpeg
https://youtu.be/VYQQD0KNOis
This hypothesis that RNA could be the first geneticmaterial is called the RNA world hypothesis.
Read more
The RNA world hypothesishttp://www.nature.com/scitable/content/the-rna-world-10239
https://youtu.be/jfq5-i8xoIU
RNA (ribonucleic acid) may have been the first genetic material since it has diverse properties.• May store information • Self-replication (non-enzymatic in certain cases) • Acts as a catalyst
Stage 4: Developing inheritanceThe first cells must have arisen from non-living material
http://biology-forums.com/gallery/195549_23_08_14_12_26_47.jpeg
https://youtu.be/VYQQD0KNOis
This hypothesis that RNA could be the first geneticmaterial is called the RNA world hypothesis.
Read more
The RNA world hypothesishttp://www.nature.com/scitable/content/the-rna-world-10239
https://youtu.be/jfq5-i8xoIU
Conclusion: Ribonucleic acid may have acted as the first
genetic material since (a) m
ay store information, (b
) may self-
replicate and (c) act as a catalyst.
Endosymbiosis in eukaryotesThe origin of eukaryotic cells can be explained by the endosymbiotic theory.
Eukaryotes appeared approximately 2 billion years ago, that is, 2.3 million years after bacteria.
The appearance of eukaryota coincides with an increase of oxygen in the atmosphere (2%) which yielded enough energy for membrane development, increase in size and compartmentalization. https://home.cc.umanitoba.ca/~frist/PLNT3140/l01/evolutionary_timeline.png
The endosymbiotic theoryThe endosymbiotic theory claims that mitochondria evolved from small aerobic prokaryotes who were respiring aerobically (using oxygen) and were “shallowed" by larger anaerobic bacteria.
The small aerobic bacteria were not destroyed. On the contrary, a mutualistic relationship (win-win) has developed between the two cells and this provided an evolutionary advantage.
The small aerobic bacterium evolved to be a mitochondrion. Aerobic prokaryoye
Endosymbiosis in eukaryotesThe origin of eukaryotic cells can be explained by the endosymbiotic theory.
Photosynthetic prokaryote
Similarly chloroplasts evolved from small aerobic prokaryotes who were photosynthesizing (producing oxygen) and were “shallowed" by larger anaerobic bacteria. Again a mutualistic relationship developed and the small photosynthetic bacterium evolved to be the chloroplast.
https://highered.mheducation.com/sites/9834092339/student_view0/chapter4/animation_-_endosymbiosis.html
Evidence for the symbiotic theoryResemblance of mitochondria and chloroplasts, with bacteria: • Mitochondria and chloroplasts are produced by
division of pre-existing mitochondria and chloroplasts.
• Have their own 70s ribosomes, resembling the bacterial 70s ribosomes.
• Have their own genes, which may transcribe, produce mRNA and translate to produce own proteins.
• Their DNA is circular resembling that of the prokaryotes.
The first synthetic cellDaniel Gibson and his colleagues at the J. Craig Venter Institute in Rockville, Maryland, synthesized the genome of the bacterium Mycoplasma mycoides, consisting of about 1.1 million base pairs.
Having assembled the genome inside a yeast cell, they transplanted it into a cell from a closely related species, Mycoplasma capricolum.
After the newly made cell divided, the cells of the bacterial colony that formed contained only proteins characteristic of M. mycoides
http://www.nature.com/news/2010/100520/full/news.2010.253.html http://www.nature.com/news/2007/070628/full/news070625-9.html
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