Origin of life Flashcards
Most biologists now think that chemical and physical processes on Earth produced _____________
Most biologists now think that chemical and physical processes on Earth produced simple cells
origin of life Requires a sequence of four main stages:
- The abiotic (nonliving) synthesis of small organic molecules
- The joining of these small molecules into macromolecules
- The packaging of these molecules into protocells
- The origin of self-replicating molecules that eventually made inheritance possible
why couldn’t life originate or survie on earth For the first few hundred million years?
(2)
- The planet was still being bombarded by huge chunks of rock + ice left over from the formation of the solar system
- Collisions generated enough heat to vaporize the available water + prevent seas from forming
Abiotic Synthesis of organic compounds on early earth
- Life originated under very different conditions than those experienced today
- First atmosphere → thick with water vapor
- Reducing athmosphere: poor in oxygen, molecules donate electrons, which allowed formation of organic compounds from simple molecules
Oparin-Haldane hypothesis-Primitive soup
Hypothesis that the Earth’s early atmosphere was a reducing (electron-adding) environment
Oparin-Haldane hypothesis-Primitive soup - 4 conditions
- No free oxygen
- Source of energy (volcanism, thunderstorms, lightning, and UV radiation
- Chemical building block (water, ions, and dissolved gasses)
- Lots of time!
Testing the primitive soup hypothesis - results
Apparatus yielded a variety of amino acids found in organisms today + other organic compounds
Second source of organic molecules
+ why
meteorites - contained more than 80 amino acids (Not made on earth → exist as isomers not present on earth)
Abiotic synthesis of Macromolecules
- RNA monomers can occur spontaneously from simple precursor molecules
- Dripping solutions of amino acids or RNA nucleotides into hot sand → researchers have produced polymers of these molecules
The packaging of these molecules into Protobionts (protocells)
- All organisms must be able to carry out reproduction and energy processing (metabolism)
- Vesicles can form spontaneously when lipids or other organic molecules are added to water
Experiments have shown that some vesicles have a ____________
Experiments have shown that some vesicles have a selectively permeable bilayer
The origin of self-replicating molecules that eventually made inheritance possible
- First genetic material most likely RNA, not DNA
- A vesicle with self-replicating, catalytic RNA would differ from its neighbors
- If the vesicle could grow, split + pass on RNA to daughters - Would be protocells that had some of the properties of their parent
- First protocells must have carried limited amounts of genetic material
- Most successful of the early protocells would have increased in number
why was the first genetic material most likely RNA, not DNA
(3)
- Ribosomes (RNA enzymes) can make copies of RNA
- RNA could catalyze protein foundation
- RNA is more flexible than DNA
what happened as DNA appeared
RNA molecules began to take on present day roles as regulators & intermediates in translation of genes
RNA → template on which DNA nucleotides were assembled
Double-stranded DNA is more stable for genetic information than RNA + can be replicated more easily
who were the first single-celled organisms
Prokaryotes
Stromatolites
layered rocks that form when certain prokaryotes bind thin films of sediment together
The earliest direct evidence of life comes from fossilized _______
The earliest direct evidence of life comes from fossilized stromatolites
what replaced probionts
Organisms that could produce all their needed compounds from molecules in their environment
Autotrophs
Organisms that can produce their own food using light, water, CO2…
Photosynthesis and the oxygen revolution
- Most atmospheric oxygen gas is of biological origin, produced during photosynthesis
- The amount of atmospheric O2 increased gradually, but then shot up relatively rapid
- Diverse adaptations to the changing atmosphere evolved
adaptation of the oxygen revolution
Cellular respiration!
* Uses O2 in the process of harvesting the energy stored in organic molecules
Diversification of ____________ allowed the emergence of ________
Diversification of autotrophs allowed the emergence of heterotrophs
Heterotrophs could live on _____________
Heterotrophs could live on molecules produced by autotrophs
