BIOL 2002 Chapter Notes - Chapter 22: Cyanobacteria, Radiometric Dating, Reducing Atmosphere

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5 Feb 2017
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Evolution
- Populations of organisms evolve from one generation to the next
- Living organisms interact with their environment
- Structure determines function
- All species are related by an evolutionary history
- Biology is an experimental science
22.1 origin of life on earth
- Stage 1: organic molecules formed prior to the existence of cells
- Nucleotides and amino acids arose spontaneously under conditions of early
earth
- Termed prebiotic synthesis - primordial soup (accumulation of molecules)
- Hypothesis 1 - reducing atmosphere of water vapor, hydrogen gas, methane and
ammonia allowed formation of organic molecules
- Miller Urey experiment
- Extraterrestrial hypothesis - meteorites carried organic molecules to earth
(carbonaceous chondrites); controversy about heat of meteorites would kill
molecules
- Deep sea vent hypothesis - superheated water rich in metal ions + hydrogen
sulfide mix with cold sea water, organic molecules form in the temperature
gradient
- Stage 2: organic polymers may have formed on the surface of clay
- More complex polymers = DNA, RNA, proteins
- Many clay materials are known to bind organic molecules
- 30-60 monomers needed to make a genetic system
- Stage 3: cell like structures may have originated when polymers were enclosed by a
boundary
- Protobiont = aggregate of prebiotically produced molecules and macromolecules
that have a boundary which allows different internal and external environments
- Polymers inside protobiont contained information; others had catalytic functions
- Eventually developed ability to self replicate
- Coacervates = droplets that form spontaneously from the association of charged
polymers such as proteins surrounded by water
- Enzymes in coacervates can have metabolic functions
- Liposomes = vesicles surrounded by a lipid bilayer; selectively permeable and
can store energy
- Stage 4: cellular characteristics may have evolved via chemical selection beginning with
an RNA world
- RNA favored to be the first macromolecule because:
- It can store information in nucleotide base sequence
- Has the capacity for self replication
- Can perform some catalytic functions like ribozymes
- DNA and proteins are not as versatile
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