Lecture 15: The Great Oxygenation Event

Question 1

Know when the Great Oxygenation event occurred, and what organisms/process contributed to this event

Answer 1

When it occurred
-Around 2.5 BYA

What organism contributed to the event?

• Cyanobacteria: Developed photosystem in which water replaced H2S in redox reactions
• Resulted in oxygen as waste product instead of sulfur

What process contributed to the event?

• Aerobic respiration
• There was an increase in oxygen
• At some point when oxygen was increasing it was absorbed by rocks and once the production was saturated then it started going to the atmosphere

Question 2

Identify microorganisms based on oxygen requirements

Answer 2

Identify microorganisms based on oxygen requirements
Obligate Aerobes: Requires oxygen

Facultative anaerobes: Uses oxygen when it is there, but they can choose if they use it or not

Aerotolerant anaerobes: They don’t care that oxygen is there, but they won’t use oxygen

Strict anaerobes: They cannot tolerate oxygen

Microaerophile: They prefer lower oxygen levels

Question 3

What were the ROS?

Answer 3

O2 -> O2 (superoxide radical)

• > H2O2 (hydrogen peroxide)
• > OH (hydroxyl radical)

Question 4

What paved the way to an oxygenated world?

Answer 4

-Oxygenic photosynthesis paved the way to an oxygenated world

Question 5

Describe why the presence of oxygen was a bad thing for life.

Answer 5

Describe why the presence of oxygen was a bad thing for life.

• A huge mass extinction
• Reactant oxygen species
• Oxygen is very electronegative so it takes away a lot of electrons
• We now have less electrons in the ETC
• This means we have less ATP
• This makes it so that there is less free energy to do growth so slower growth

Question 6

Describe why the presence of oxygen was a good thing for life.

Answer 6

• Develop enzymes that can deal with the oxygen
• They can live in different environments
• Cells develop slime layers that help it so that oxygen doesn’t get in
• Develop aerobic respiration
• Use O2 as terminal electron acceptor
• More ATP because more free energy so more growth

Question 7

How did organisms make detoxification of Reactive Oxygen Species (ROS) possible?

Answer 7

Aerobic respiration constantly generates reactive oxygen species (ROS), so even organisms developed enzymes to break down toxic byproducts.

Question 8

What enzyme did organisms use to detoxify

O2-> O2 (superoxide radical)?

Answer 8

Enzyme: superoxide dismutase

Broke down O2-> O2 to
O2 + H2O2

Question 9

What enzyme(s) did organisms use to detoxify
H2O2 (hydrogen peroxide)?

Answer 9

Enzyme: catalase

Broke down H2O2 (hydrogen peroxide) to
O2 + 2H2O

Enzyme: perioxidase

Broke down H2O2 (hydrogen peroxide) to
NAD+ + 2H2O

Question 10

Describe the effects of increasing oxygen concentration on microbial growth and life.

Answer 10

• Organisms that were efficient at hot temps needed to adjust since earths temp was decrease
• We had more CO2 and so then we had more water
• New organisms that needed different amounts of oxygen