Module 1 - Origin of life Flashcards
What were the conditions on early Earth and which ones made it inhospitable for life?
- Very high temperatures
- Atmosphere - high amounts of CO₂, CH₄, and NH₃
- Lack of Ozone layer (no O₂ in the atmosphere)
- No water
- High levels of UV rays
inhospitable -> Temps, UV rays, and water
What evidence is there for early life forms?
Stromatolites - Calcareous mounds made of layers of lime-secreting bacteria and trapped sediment
Microfossils in ancient rocks
Carbon isotope analysis - the lighter C¹² isotope is preferred in organisms so finding an abundance of C¹² in comparison to C¹³ is a sign of life
Prebiotic soup theory: who proposed it and what did it mean?
Haldane and Oparin
Energy provided by UV light/lightning/volcanoes formed organic molecules in the oceans.
The Miller-Urey experiment: what was it and what is a major critique of it?
An experiment used to show that organic material could have been formed from inorganic material in the early Earth’s atmosphere
The major critique of the experiment is that the gas used in the experiment did not accurately represent the gas in the atmosphere at the time
Why are deep sea vents likely the site of the first forms of life?
There is an abundance of consistent chemical energy sources
Protected from what was likely to have been very hostile conditions on the surface
The potential for mineral compartmentalisation in these structures
Why is RNA preferred over DNA as the hypothetical initial replicating polymer?
- RNAs have been shown to self replicate
- RNA is derived from DNA via transcription
- RNAs can have inherent enzymatic activity
- RNA is typically single-stranded so it can form complex structures via base pairing
The proposed first stages of cellular life development
1) The prebiotic synthesis of RNA/proteins from inorganic sources
2) self-replicating RNAs form
3) lipid bounded vesicles form containing RNAs
4) proteins take over catalytic function from RNAs
5) DNA, a more stable molecule, evolves as the coding polymer from RNA
Why do we use a “correction” stage when building phylogenetic trees?
- To account for multiple mutations at a single site.
- Observed distances are likely to be smaller than the actual distances.
- To account for reversions.
Why has the 16S rRNA gene become the most widely used sequence for bacterial phylogenetics?
It’s a core component of the translation machinery and is present in all bacterial species.
What was Carl Woese’s key discovery based on using rRNA sequences to infer phylogenies?
The existence of a third Domain of Life termed the Archaea
Oxidation
The loss of electron/gain of oxygen/increase in oxidation state
Fermentation
Anaerobic catabolism of organic material where they act as both the electron donator and acceptor and the ATP is generated via substrate-level phosphorylate
Autotroph
Organisms that produce their own carbon compounds, mainly by using CO₂
Phototroph
An organism that uses light energy for photosynthesis to manufacture carbon compounds
Chemoorganotroph
An organism that gets energy from the oxidation of reduced organic material
