Lecture 3C: Anaerobic Respiration and Fermentation: Nitrate Reduction and Denitrification, Sulfate and Sulfur Reduction Flashcards
Energy Production and Primary Metabolism
Nitrate Reduction and Denitrification
What is the common electron acceptor in nitrate reduction?
Nitrate (NO₃⁻)
Nitrate Reduction and Denitrification
What is the first product in nitrate reduction?
Nitrite (NO₂⁻)
Nitrate Reduction and Denitrification
What gaseous products are formed in denitrification?
Give three (3)
- nitric oxide (NO)
- nitrous oxide (N₂O)
- dinitrogen (N₂)
Nitrate Reduction and Denitrification
What microorganism reduces nitrate (NO₃⁻) to nitrtite (NO₂⁻) but does not denitrify fully?
Escherichia coli
Explanation:
*Escherichia coli *reduces NO₃⁻ (nitrate) to NO₂⁻ (nitrite) through nitrate reduction, but it does not perform complete denitrification (which would convert nitrite to N₂ gas). This is because *E. coli *lacks the necessary enzymes (e.g., nitrite reductase, nitric oxide reductase, and nitrous oxide reductase) required for the full denitrification pathway. Instead, it primarily uses nitrate reduction as an anaerobic respiration process.
Nitrate Reduction and Denitrification
What enzyme catalyzes nitrate (NO₃⁻) to nitrtite (NO₂⁻)?
Nitrate reductase
Explanation:
- It catalyzes the reduction of nitrate (NO₃⁻) to nitrite (NO₂⁻) by facilitating the gain of electrons (reduction) in the chemical reaction.
- nitrate reductase enables the conversion of nitrate to nitrite by adding electrons, often using electron donors like NADH or NADPH in the process.
Nitrate Reduction and Denitrification
What enzyme catalyzes nitrite (NO₂⁻) to nitric oxide (NO)?
Nitrite reductase
Nitrate Reduction and Denitrification
What enzyme catalyzes nitric oxide (NO) to nitrous oxide (N₂O)?
Nitric oxide reductase
Nitrate Reduction and Denitrification
What enzyme catalyzes nitrous oxide (N₂O) to dinitrogen (N₂)?
Nitrous oxide reductase
Nitrate Reduction and Denitrification
What type of bacteria are strong denitrifiers?
Give one (1); what species?
Pseudomonas species
Nitrate Reduction and Denitrification
What phylum do many denitrifying bacteria belong to?
Proteobacteria
Nitrate Reduction and Denitrification
What ecological impact does denitrification have on agriculture?
Removes nitrate fertilizers
Explanation: While denitrification helps prevent nitrate accumulation in water bodies (thus reducing water pollution and eutrophication), it can also lead to decreased soil fertility and reduced crop yields due to the loss of available nitrogen, which is essential for plant growth.
Nitrate Reduction and Denitrification
What greenhouse gas is released during denitrification?
Additional question: How does it contribute to climate change?
Nitrous oxide (N₂O)
- N₂O is a potent greenhouse gas, with a global warming potential approximately 298 times greater than CO₂ over a 100-year period. This means it traps significantly more heat in the atmosphere than carbon dioxide.
- Nitrous oxide has a long atmospheric lifetime, lasting over 100 years. This allows it to persist in the atmosphere and contribute to warming over an extended period.
- N₂O also contributes to the depletion of the ozone layer when it breaks down in the stratosphere, releasing nitrogen oxides that can destroy ozone molecules. A healthy ozone layer is crucial for protecting the Earth from harmful ultraviolet radiation.
Nitrate Reduction and Denitrification
What environmental issue is caused by NO reacting with ozone?
Acid rain
Nitrate Reduction and Denitrification
How is denitrification beneficial in sewage treatment?
Removes excess nitrogen
Explanation:
Denitrification in sewage treatment is beneficial because it removes excess nitrogen by converting nitrate and nitrite into nitrogen gas (N₂). This process helps prevent eutrophication, improves water quality, and supports sustainable treatment practices by reducing nitrogen levels in wastewater before it is released into the environment.
Nitrate Reduction and Denitrification
What element is present in nitrate reductase?
Molybdenum
Explanation:
Molybdenum acts as a cofactor in the enzyme’s active site, facilitating the reduction of nitrate (NO₃⁻) to nitrite (NO₂⁻) by participating in the electron transfer process during the reaction. This element is crucial for the enzymatic activity of nitrate reductase and plays a key role in nitrogen metabolism in various organisms.
Nitrate Reduction and Denitrification
What represses the synthesis of nitrate reductase?
Oxygen (O₂)
- In the presence of oxygen, bacteria prefer to use aerobic respiration, which is more efficient for energy production.
- Nitrate reduction is often used under anaerobic or low-oxygen conditions.
Nitrate Reduction and Denitrification
What bacterium performs full denitrification?
Give two (2)
- Paracoccus denitrificans
- Pseudomonas stutzeri
Nitrate Reduction and Denitrification
- What nitrogen compound has an oxidation state of +5?
- What nitrogen compound has an oxidation state of -3?
- What nitrogen compound has an oxidation state of 0?
- Nitrate (NO₃⁻)
- Ammonia (NH₃)
- Nitrogen gas (N₂)
Explanation:
1. Nitrate (NO₃⁻, +5): Its high oxidation state means it can act as an electron acceptor in anaerobic respiration (denitrification).
2. Ammonia (NH₃, -3):The -3 oxidation state represents the most reduced form of nitrogen, making it readily usable by organisms.
3. Nitrogen Gas (N₂, 0): The oxidation state of 0 signifies that nitrogen atoms in N₂ are neither electron-rich nor electron-deficient. This, combined with the strong triple bond between the nitrogen atoms, makes N₂ relatively unreactive (inert). This inertness is why N₂ makes up about 78% of the Earth’s atmosphere.
Nitrate Reduction and Denitrification
What is the significance of gaseous products in denitrification?
They escape into the environment
Sulfur and Sulfate Reduction
What is the primary electron acceptor in sulfate reduction?
Sulfate (SO₄²⁻)
Sulfur and Sulfate Reduction
What is the main product of sulfate reduction?
Hydrogen sulfide (H₂S)
Sulfur and Sulfate Reduction
Which group of bacteria is known for sulfate reduction?
Sulfate-reducing bacteria (SRB)
Sulfur and Sulfate Reduction
- What sulfur compound has an oxidation state of +6?
- What sulfur compound has an oxidation state of -2?
- Sulfate (SO₄²⁻)
- Hydrogen sulfide (H₂S)
Explanation:
Sulfate (SO₄²⁻, +6):
* The +6 oxidation state represents the most oxidized form of sulfur.
* Sulfur in sulfate has a +6 oxidation state, meaning it has lost electrons compared to its neutral state.
* This makes sulfate an oxidizing agent, meaning it tends to accept electrons from other substances.
Hydrogen Sulfide (H₂S, -2):
* The -2 oxidation state represents the most reduced form of sulfur.
* Sulfur in hydrogen sulfide has a -2 oxidation state, meaning it has gained electrons compared to its neutral state.
* This makes hydrogen sulfide a reducing agent, meaning it tends to donate electrons to other substances.
Sulfur and Sulfate Reduction
