Nitrogen, Oxygen, Phosphorus and Sulphur and the Origins of Life Flashcards
What were some of the major components of the early atmosphere of the Earth?
Hydrogen and helium (lost to space as geological time proceeded)
Carbon dioxide (from volcanoes – plus trace amounts of carbon monoxide)
Water (vapour – condensed to form oceans)
Sulphur dioxide (formed sulphates)
Sulphur (formed sulphides)
Nitrogen
Ammonia
Methane
NO OXYGEN!= Combined in the form of gaseous oxides such as H2O and SO2 or minerals
How did primitive cyanobacteria generate molecular oxygen?
Used water as an electron donor in a redox process= Reducing agent
Higher forms of life can then use the oxygen as an electron acceptor
How would have early life have had access to nitrogen?
In the form of ammonia (NH3 or NH4+)= Much preferred form for nitrogen assimilation today
Nitrate reduction to ammonia= Energetically expensive process and is avoided where possible by modern organisms
Nitrogen fixation= Energetically expensive and is very sensitive to atmospheric oxygen
What happens to reduced forms of phosphorus in the presence of water?
Highly unstable in presence= some compounds such as PCL3 and PF5 spontaneously decompose to phosphates in the presence of water
How would have early life have had access to phosphorus?
Phosphates leaching from minerals into water pools= mainly found in the form of phosphates
How would have early life have had access to sulphur?
Available in the reduced form
Sulphur dioxide (SO2)= produced by volcanoes
Minerals containing reduced sulphur were abundant but sulphates are rare
What is the iron-sulphur theory of the Origin of Life?
Naturally occurring iron sulphide crystals= Can catalyse both oxidation-reduction reactions (produces energy) and the polymerisation of amino acids
Active self-sustaining metabolic system= Works especially well in deep ocean vents (black smokers)
What are some primitive organisms in extreme environments which live now which may be similar to early organisms?
Purple and green photosynthetic bacteria can use sulphides as electron donors in redox reactions
Deep sea hydrothermal vents support a diverse animal population such as large tube worms
-Large tube worms: Contain sulphur bacteria as symbionts (trophosome)
-Pigments able to collect H2S and O2 from sea water (through specially modified haemoglobin) –> Supply the trophosome with the H2S and O2 and CO2 from respiration
-Oxidise the sulphide to produce energy and fix carbon dioxide to produce organic compounds
-Animal can then feed on the organic compounds= Produce CO2
Animal does not need external sources nutrition!
How do methanogens generate energy by anaerobically?
CO2 + 4H2 ––––> CH4 + 2H2O
where H2 is oxidised and CO2 is reduced
Overall process is coupled to ATP production and H@ is used to reduce a mixed disulphide as the ‘end point’ in an electron transport chain
