Origin of life Flashcards
what is the early history of planet earth
-4,600 Earth formed by the gravitational accumulation of dust and larger objects. The mass melts and begins to differentiate into the core, mantle and crust. Water vapour and various gasses are outgassed but do not accumulate due to the great heat and continual bombardment as new material is accumulated. The Moon forms during a major collision.
-3,750 Age of the oldest rocks on Earth (Isua Supercrustal Group from Greenland). Earth has cooled to the extent that a crust begins to solidify. As temperatures continue to fall the oceans and atmosphere can potentially begin to condense out.
-> 3,800 Progress retarded by continued bombardment of large objects. Released energy is sufficient to boil off the oceans and atmosphere (along with any prebiotic organic compounds).
-< 3,800 Meteorite bombardment decreases in intensity and the planet cools below a threshold that allows oceans and atmosphere to condense out. Organic compounds begin to be synthesized and accumulate.
-By 3,800 Ma we have conditions on planet earth we believe suitable for life to have originated (?RNA world?).
-3,500 The earliest fossil evidence for life on earth.
plant earth at age 4600 Ma
-Earth formed by the gravitational accumulation of dust and larger objects. The mass melts and begins to differentiate into the core, mantle and crust. Water vapour and various gasses are outgassed but do not accumulate due to the great heat and continual bombardment as new material is accumulated (lots of chunks of rocks). The Moon forms during a major collision.
-debris clumped together due to gravity
-core= iron and nickel
-mantle= manganese and silica
-crust= silicone and aluminium
-mass melts because gets to big+ gravity
-moon= orbit from a part of the bombardment which has been thrown out
planet earth at 3750 Ma
-Age of the oldest rocks on Earth (Isua Supercrustal Group from Greenland). Earth has cooled to the extent that a crust begins to solidify. As temperatures continue to fall the oceans and atmosphere can potentially begin to condense out.
-crust began to solidify
-took so long to cool because of the moon- it covered in craters formed in period 3.1-8 billion year
-crater= leads to bombardment
-the moon was a dead planet for a long time
planet earth at age > 3800
-Progress retarded by continued bombardment of large objects. Released energy is sufficient to boil off the oceans and atmosphere (along with any prebiotic organic compounds).
planet earth at age < 3800
-Meteorite bombardment decreases in intensity and the planet
cools below a threshold that allows oceans and atmosphere to
condense out. Organic compounds begin to be synthesized and
accumulate.
what was the early earths atmosphere like
-formed by volcanic outgassing of water vapour + N2 (and its oxides), CO2, CH4, NH3, H2 & H2S. The water vapour gradually condenses to form the oceans and the H2 is lost into space
what was planet earth like at 3500
-The earliest fossil evidence for life on earth
whats panspemia
-suggests life appeared on the planet- life formed elsewhere and transported- some think this is impossible
-doesnt solve the issue of origin of life
what are the Approaches to solving the origin of life
1) Analyze living prokaryotes and attempt to reconstruct their common ancestor (essentially the simplest conceivable prokaryote)
2) Compare duplicated genes potentially enabling us to reach back beyond that ancestor and estimate some of the earliest components of genetic machinery.
3) Reconstruct conditions that existed on Earth in these remote times and simulate these experimentally and see what is produced.
why are prokaryotes believed to have originated before eukaryotes
1) They appear earlier in the fossil record
2) They are simpler in virtually every aspect
3) There is evidence that eukaryotes evolved from prokaryotes
what are the Fundamental similarities between prokaryotes and eukaryotes
1) The method of transmitting information in triplet code in DNA and translating it into proteins through RNA.
2) In living organisms all amino acids are laevo-rotatory and in nucleic acids all the sugars are dextro-rotatory.
what are the Chemicals produced by simulating conditions on the primitive Earth
-Amino acids
=Including all of the biologically important ones.
-Purines/Pyrimidines
=Including the four bases of RNA (adenine, cytosine, guanine and uracil) but not thymine which replaces uracil in DNA)
-Sugars
-Porphyrins
=(molecules which are the forerunners of important biological compounds like vitamin B12, chlorophylls etc.)
-Complex tar-like substances which defy analysis
-similar chemicals also appear in space
why is life commonly seen as evolved through basic chemistry
-We have seen that the necessary materials were available. There are a variety of possible environments in which life could have formed and a number of possible energy sources:-
*sun (UV radiation)
*radioactivity
*electric discharges (e.g. lightening)
*volcanic (hot springs, black smokers etc.)
whats the RNA world
-All living organisms use the same basic machinery—information is stored in DNA and transcribed and translated into protein using RNA.
-What came first, DNA or proteins, given that proteins are the end product but are essential as enzymes in translating and copying the information in DNA.
-A dramatic breakthrough occurred in the 1980s when when self splicing RNA was discovered.
-Speculation on the origin of life began to centre on a “RNA world”.
-For RNA world we have the basic chemicals, replication mechanisms and the energy sources.
what are the novel metabolic pathways
-Chemoautotrophs (energy from oxidising inorganic substance—e.g. H2S, NH3, Fe2+ etc.; C source CO2)
-Chemoheterotrophs (energy and C source from consuming organic compounds)
-Photoautotrophs (energy from light; C source CO2)
-Photoheterotrophs (energy from light; C source from consuming organic material)
-needs cytochromes and porphyrins
what are cytochromes
-the basis of oxygen metabolism
cytochromes and porphoryins
-Obligate anaerobes (poisoned by O2 and live exclusively by fermentation or anaerobic respiration)
-Aerotolerant organisms (cannot use O2 for growth, but tolerate its presence, and live by fermentation)
-Facultative anaerobes (use O2 if it is present but can live by fermentation in an anaerobic environment)
-Obligate aerobes (use O2 for cellular respiration and cannot live without it)
