Nitrate reduction

Question 1

Does anaerobic respiration use electron transport chains?

Answer 1

Yes

Question 2

Does anaerobic respiration generate a PMF?

Answer 2

Yes

Question 3

What is the terminal electron acceptor of anaerobic respiration?

Answer 3

An inorganic molecule that isn’t O2

Question 4

What are 4 possible terminal electron acceptors of anaerobic respiration? What are they reduced to?

Answer 4

Nitrate: reduced to nitrite or nitrogen gas
Ferric iron (III): reduced to iron (II)
Sulfate: reduced to hydrogen sulfide
Carbonate: reduced to methane and acetate

Question 5

Why isn’t anaerobic respiration as good as aerobic respiration?

Answer 5

The TEA aren’t as electropositive, so the electrons from NADH and FADH2 don’t release as much energy when they go through the ETC

Question 6

Is anaerobic respiration better than fermentation for energy production?

Answer 6

Yes, produces way more ATP

Question 7

What is the terminal electron acceptor of nitrate reduction?

Answer 7

Nitrate

Question 8

What is the first step of nitrate reduction?

Answer 8

Nitrate reduction by nitrate reductase to produce nitrite

Question 9

Do all nitrate-reducing bacteria go to the end of the pathway?

Answer 9

No, some only do the nitrate reduction and stop, then excrete the nitrite as waste

Question 10

What conditions need to be present for nitrate reductase to be expressed?

Answer 10

Absence of oxygen and the presence of nitrate

Question 11

Why is the absence of oxygen required for nitrate reduction to occur?

Answer 11

If there’s oxygen around, the bacteria will use aerobic respiration instead because it generates more energy

Question 12

Why does nitrate reduction produce less PMF and ATP than aerobic respiration?

Answer 12

Nitrate isn’t as electropositive as oxygen, so there isn’t as many steps in the ETC before the electrons reach NO3-. There are fewer proton pumping events, so less PMF is generated, and less ATP is produced

Question 13

What is the full nitrate reduction pathway?

Answer 13

Nitrate (NO3-) -> nitrite (NO2-) -> nitric oxide (NO) -> nitrous oxide (N2O) -> nitrogen (N2)

Question 14

What is denitrification?

Answer 14

The rest of the nitrate reduction pathway. Involves the conversion from fixed nitrogen to gaseous nitrogen

Question 15

Why would a bacteria want to do denitrification?

Answer 15

Involves an extra proton pumping event, so generates a little more PMF and a little more ATP

Question 16

Do all nitrate reducing bacteria do denitrification?

Answer 16

No, only some

Question 17

Why is denitrification good for sewage treatment?

Answer 17

Removed fixed nitrogen from sewage, which would otherwise cause eutrophication

Question 18

Why is denitrification bad for agriculture?

Answer 18

Fixed nitrogen that can be used by plants is lost to the atmosphere, which means the plants can’t grow as well and the farmers have to spend a lot of money on fertilizers