Lecture 3C Flashcards
What is the terminal electron acceptor in aerobic respiration?
Oxygen
What is chemolithotrophy?
A process where inorganic compounds (like H₂, reduced sulfur, or ammonia) serve as electron donors.
What is carbon dioxide fixation?
The process of incorporating CO₂ into organic molecules.
What is the reductive acetyl-CoA pathway?
An alternative carbon fixation pathway used by some anaerobes.
Why are strict anaerobes unable to survive in oxygen?
They lack enzymes to detoxify toxic aerobic metabolism products.
Give an example of anaerobic respiration.
Nitrate reduction or denitrification.
What is denitrification?
The conversion of nitrate (NO₃⁻) to nitrogen gas (N₂), often through intermediates like NO and N₂O.
Why is denitrification ecologically significant?
It removes fixed nitrogen from ecosystems, affecting agriculture and contributing to greenhouse gas emissions.
What are common electron acceptors in anaerobic respiration?
Nitrate, sulfate, and ferric iron.
What is a true denitrifier?
A microorganism that can convert NO₃⁻ fully to N₂, like Pseudomonas stutzeri.
Why is NO₂⁻ (nitrite) important in nitrate reduction?
It is an intermediate in the reduction of NO₃⁻ to N₂.
What type of bacteria typically perform denitrification?
Facultative anaerobes, such as Pseudomonas species.
What gases are released during denitrification?
NO, N₂O, and N₂.
Why is N₂O a concern for the environment?
It is a strong greenhouse gas.
What is the role of nitrate reductase in nitrate reduction?
It catalyzes the first step of NO₃⁻ reduction.
What represses nitrate reductase activity?
Oxygen (O₂).
What happens when NO₂⁻ is further reduced?
It can form NO, N₂O, or N₂.
Why is denitrification undesirable in agriculture?
It removes nitrate fertilizer from the soil.
How does denitrification impact water bodies?
It can prevent algal blooms by removing excess nitrogen.
Which microorganism is capable of nitrate-based anaerobic respiration?
E. coli.
What is the electron donor in nitrate reduction?
NADH.
What is the final electron acceptor in denitrification?
Nitrogen gas (N₂).
Where does nitrate reduction occur in bacteria?
In the cytoplasmic membrane.
What is ubiquinol’s role in nitrate reduction?
It helps transfer electrons from NADH to the electron transport chain.
What happens in the periplasmic space during denitrification?
Electron ions accumulate, creating a proton motive force.
What enzyme reduces NO₂⁻ to NO?
Nitrite reductase.
What enzyme reduces NO to N₂O?
Nitric oxide reductase.
What enzyme reduces N₂O to N₂?
Nitrous oxide reductase.
What is the key difference between nitrate reduction and denitrification?
Nitrate reduction only produces NO₂⁻, while denitrification converts NO₃⁻ to N₂.
What enzyme catalyzes sulfate reduction?
Sulfate reductase.
What is the end product of sulfate reduction?
Hydrogen sulfide (H₂S).
What is an example of a sulfate-reducing bacterium?
Desulfovibrio desulfuricans.
What is the role of hydrogen in sulfate reduction?
It serves as an electron donor.
What are the two activated sulfate intermediates in sulfate reduction?
APS (adenosine 5’-phosphosulfate) and PAPS (phosphoadenosine 5’-phosphosulfate).
Why is APS important in sulfate reduction?
It activates sulfate to make reduction more thermodynamically favorable.
What enzyme reduces APS to SO₃²⁻?
APS reductase.
What enzyme reduces SO₃²⁻ to H₂S?
Sulfite reductase.
What is the role of cytochromes in sulfate reduction?
They help transfer electrons through the electron transport chain.
What is hydrogenase’s function in sulfate reduction?
It oxidizes H₂ to release electrons.
How does sulfate reduction contribute to ATP production?
It generates a proton motive force for ATP synthesis.
What is the difference between assimilative and dissimilative sulfate metabolism?
Assimilative is for biosynthesis, while dissimilative is for energy conservation.
What is the major environmental impact of sulfate reduction?
Production of H₂S, which can contribute to acid rain and corrosion.
What is anammox?
Anaerobic ammonia oxidation, an alternative nitrogen removal process.
Why are denitrifiers considered metabolically diverse?
They can use multiple electron acceptors and even ferment.
What is the role of Fe/S complexes in anaerobic respiration?
They transfer electrons from NADH to the electron transport chain.
What happens to nitrate in the presence of oxygen?
Nitrate reductase activity is repressed.
What alternative electron acceptor can denitrifying bacteria use besides nitrate?
Ferric iron (Fe³⁺).
What is the key function of cytochrome b in denitrification?
It helps transfer electrons to the final electron acceptor.
What is the consequence of excess nitrogen in water systems?
Algal blooms and eutrophication.
What is the overall importance of anaerobic respiration in ecosystems?
It recycles nutrients, removes excess nitrogen, and contributes to greenhouse gas emissions.
