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25 Cards in this Set
- Front
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What are the 2 theories of evolution of prokaryotic cells? |
Panspermia Theory The molecule os life or life itself arrived from extraterrestrial sources Chemical evolution Theory Life is a result of chemical evolution on earth so all initial components for life were already present on earth so, when exposed to correct conditions, simple cells could potentially form |
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What is the theory of evolution of eukaryotic cells? |
Serial Endosymbiosis theory • Suggest mitochondria and plastids originated as small prokaryotic cells that lived within larger ancestral eukaryotic cells - protoeukaryotes
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What is an endosymbiant? |
An organism living inside a cell of another organism which has evolved with host cells into a single organism |
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What are 2 pieces of evidence supporting the panspermia theory? |
• 1984 meteorite found in antarctica contained water, simple C molecules an magnetite which are molecules formed by living organism • 1969 Murchison meteorite found in australia that contained unique molecules to life including; nucleotides, amino acids, lipids and simple sugars |
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What is the counter argument for evidence for the panspermia theory? |
• Unlikely organisms will survive thousands of years of space travel • Most living or organic matter wouldn't survive entry through earths atmosphere • Could be contaminated by earths atmosphere when opened for sampling |
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What are the 4 main steps of the chemical evolution theory? |
1. Abiotic synthesis of small organic molecules(amino acids and nitrogenous bases) 2. Joining together of these forming nucleic acids and proteins 3. Enclosing these molecules by membranes forming protocells/protobionts 4. Origin of self replication molecules that allow self-inheritance |
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What was the theory behind the Abiotic synthesis of organic molecules? Provide experimental evidence behind this. |
Primordial soup theory - 1924 Ocean was a solution of organic molecules Reducing atmosphere on early earth Was tested in 1953 by Milier and Urey with a system with a reducing atmosphere. Their system contained amino acids and nucleotides within days |
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In what way could the abiotic synthesis of organic molecules still occur if a reducing atmosphere was not present? Provide evidence. |
Formation could've occurred at hydrothermal vents on sea floor near volcanoes and tectonic plates. These have very high temperatures and reducing atmospheres. EVIDENCE: archaea are found to populate those areas in present day |
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How does the abiotic joining of nucleotides and amino acids occur? |
Condensation polymerisation to form proteins and nucleic acids. Atmosphere needs to allow for this polymerisation of monomers to polymers - ideal environments are hot clay, rock or sand where molecules aggregate on the surface before polymerisation occurs Polymerisation can also occur spontaneously |
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What is the ideal environment for polymerisation of the abiotically formed nucleotides and amino acids? |
Hot sand, rock or clay which allows molecules to aggregate on the surface before polymerising. Could also be spontaneous |
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Protocells |
An abiotic precursor of living cells composed of a series of abiotically produced molecules surrounded by a potentially semi-permeable membrane. Maintained a different internal chemistry than surroundings. |
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What was the membrane of a protocell potentially made from? |
Possibly formed from vesicles that were created when lipids were added to water. Random polymers could be incorporated
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Ribozymes |
Catalytic RNAs that could catalyse reactions on their own nucleotides as well as in other cellular substances. Can self-replicate and carry information which are essential requirements for inheritance |
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What was the origin of self replication in cells? - CHEMICAL EVOLUTION THEORY 4. |
Ribozyme RNA couldve provided a DNA template for nucleotide assembly |
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What changed earths atmosphere? And what was the result of this? |
Evolution of photosynthetic prokaryotes that released oxygen Mass extinction of many anaerobic prokaryotic groups |
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Theory of evolution leading to eukaryotic cells: |
Serial Endosymbiosis thoery |
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Endosymbiant |
An organism living inside the cell of another organism which has evolved with the host cell into a single organism |
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1st step of serial endosymbiosis |
Large ancestral prokaryote cell with plasma membrane and DNA |
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2nd step of serial endosymbiosis - evidence |
Infolding's of plasma membrane forms internal compartments leading to organelles Evidence: ER and nuclear envelope have similar composition to plasma membrane
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3rd step of serial endosymbiosis evidence |
Aerobic heterotrophic prokaryote engulfed by phagocytosis but not broken down by lysosomal pathways. May have initially been mutualistic symbiosis
Mitochondria are present in all eukaryotes |
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Mutualistic symbiosis Evidence in serial endosymbiosis |
The beneficial residence of one prokaryotic organism living inside another to both organisms. May have been beneficial as may've allowed prokaryotes to harness other E sources e.g. methane or oxygen |
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4th step of serial endosymbiosis |
Development of engulfed prokaryote into a semi-autonomous organelle i.e mitochondria - organisms can no longer be separated |
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Photosynthetic eukaryote evolution - evidence hint: 2 extra steps after main endosymbiosis |
5. a photosynthetic prokaryote i.e cyanobacterium is engulfed by phagocytosis, not broken down by lysosomes(initial mutualistic symbiosis) 6. Eventually may've developed into a semi-autonomous organelle i.e. chloroplasts(could form other plastids)
Only plants/protists have chloroplasts |
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Evidence for phagocytosis in serial endosymbiosis |
We can see nowdays that organisms like bacteria can be engulfed - surely small prokaryotes could be too using same mechanism |
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Evidence for prokaryotic origination of mitochondria and chloroplasts |
Similar size, physiology, organisation Division by binary fission Double membrane - inner composition similar Sensitive to some of antibiotics effecting prokaryotic ribosomes Circular DNA that can be transcribed and translated to synthesize proteins Semi-autonomous organelle |
