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
