3 -Oxygen

Question 1

What is the difference between Type I and Type II reaction centre

Answer 1

Type I: Protein take e- away
(Fe: acceptor (bound to sulphur))
-Found in: Green-sulphur bac. + Heliobac.

Type II: protein takes e- in
(Fe: donor (bound to cytochrome (e-
attracted to Fe but don’t react with it (attraction ->
to guide e- down reaction centre))))
-Found in: Purple-sulphur bac. + Green non-sulphur bac.

Question 2

Explain how Type I and II reaction centres came together in cyanobacteria and why this allowed them to use water as an electron donor

Answer 2

• Lateral Gene Transfer -bacteria can transfer DNA genes with each other (they kiss (Binham is mega gay))
• Enabled them to do oxidation of water H2O which makes sense since other organisms were able to oxidise H2S which is very chemically similar to H2O

Known as the Oxygen Evolving Complex

Question 3

What are the impacts of oxygen production on the planet

Answer 3

Triggered the Huronian Ice Age - world’s first ice age

• Methane CH4 present on earth reacts with O2 to make CO2 and water.CO2 is a greenhouse gas therefore forms a greenhouse layer where heat from the sun can’t enter the earth and leads to a global cooling

Question 4

What are the positive impacts of oxygen production/how it allowed evolution of large cells

Answer 4

After the MASS Extinction —> build up of oxygen in the atmosphere reacted with UV to make O3= ozone

+Earth was protected from the UV light hitting the earth. This means that life can move out of water and on land
+Allowed for aerobic respiraation which is more efficient- more energy from sugar = allows cells to get bigger
- BETTER RESPIRATION MEANT BIGGER CELLS
- Started the first ever food chain as cells began eating other cells=phagocytosing

Question 5

What were the negatives of oxygen and what did it cause

Answer 5

O2 can react with fe2+ (ferrous iron) can react to produce a hydroxyl radical (OH*) - most reactive radical known to man -These series of reaction is known as the FENTON REACTION

-OH* detrimental to life (Fucking obliterates cells)
-Due to early cells/life being anaerobes ->
high O2 concs -> no defences against OH*
-Lead to Mass Extinction (Oxygenation Event)