evo bio CH 17-Early Life on Earth

• Proposed ideas of the origin of life

  • Creation origins – created by a Deity

  • Panspermia – brought from somewhere else

  • Abiogenesis – natural process where life arises from non-living matter
• Abiogenesis – the only origin that science can investigate


  • Non-living organic compounds (primordial soup)

  • Gradual process of increasing complexity from energy input

  • Suggests that a hyperthermophile ( extremely hot) was the first life form
• What constitutes life?

  • Homeostasis – maintaining a stable equilibrium

  • Structural organization

  • Metabolism – control of chemical reactions

  • Growth

  • Reproduction 

  • Response to stimuli
• However life started, it was simple and then evolved
• The first life was prior to current fossils, so what was it like?

  • Combination of lipids, nucleotides, amino acids
  • Several types of protocells could assemble
  • This suggests a simple RNA start
  • Materials could be exchanged – similar to lateral gene transfer
  • First reproduction would be due to dividing
• primordial soup 


  refers to the primitive water bodies on the earth that were rich in organic matter and from which scientists believe that the first life forms evolved
• Plausibility of the prebiotic soup hypothesis


  The Miller – Urey experiment
• The Miller – Urey experiment showed that amino acids could be formed from simple organic compounds, but did not spontaneously produce life 
• In early earth conditions, did life arise more than once?
• In early earth conditions, did life arise more than once?

  Uncertain, There may have been many forms prior to the last universal common ancestor

  The LUCA has also been defined as "a hypothetical organism ancestral to all three domains"

  
• Why an RNA start instead of DNA?

  • RNA can make proteins directly from available amino acids

  • DNA requires enzymatic activity of proteins to replicate

  
• Spiegelman RNA experiments provide evidence for selection of RNA molecules for translation.
• But do we still live in an RNA world?

  • There are still RNA viruses

  • Upper limit of size is ~ 10,000 base pairs

  • DNA reduces potential for outside molecules to react and disrupt

  • DNA has proof-reading mechanism

  • DNA has much lower mutation rates

  • Still lack understanding on how the shift occurred
• Is DNA or RNA more stable?

  DNA
• viruses origin

  • Encapsulated gene hypothesis – independent existence for transposons

  • Reduction hypothesis – cellular parasites that abandoned their host

  • Relics of RNA world hypothesis
• Horizontal Gene Transfer and Early Evolution

  • May have promoted adaptation

  • Primordial life may have been many cell types exchanging genetic information

  • Evolution of more complicated cells would diminish the importance of HGT
• Properties of the Last Universal Common Ancestor

  • Probably included a set of 355 known genes (essentially found in all current life)

  • Almost certainly was anaerobic

  • Probably thermophilic
• abiogenesis


  the origin of life from nonliving matter. specifically : a theory in the evolution of early life on earth: organic molecules and subsequent simple life forms first originated from inorganic substances
• the miller - urey experiment provides evidence

  the basic building blocks of life could have emerged under early Earth's conditions, supporting the theory of abiogenesis.