Lecture 35- part 1

Question 1

How is ammonium assimilated?

Answer 1

by GS-GOGAT system

- Common in all types of cells

Question 2

What is the yield of nitrogen assimilation by GS-GOGAT?

Answer 2

• Yields GLUTAMATE from 2-oxoglutarate + NH4+

REquires ATP and NADH

Question 3

What is the reverse of ammonium assimilation?

Answer 3

Ammonification

• May enzymes (plants, animals, microbes)

Question 4

What is the purpose of assimilatory nitrate reduction? How is it done?

Answer 4

=> For cellular growth

Via assimilatory NITRATE REDUCTASE (NO3- => NO2-)

AND

Assimilatory NITRITE REDUCTASE ( NO2- => NH4+ )

Question 5

How are ANRs repressed?

Answer 5

ANR => Assimilatory NITRATE REDUCTASe is inhibited by cellular [NH4+] => limited by end-product inhibition

Question 6

Describe Dissimilatory nitrate reduction

Answer 6

Anaerobic respiration

• Via dissimilatory nitrate reductase ( NO#-=> NO2-)

Characteristic of facultative anaerobes that can use NO3- as terminal e- acceptor (TEA) when O2 is not available

Question 7

What does dissimilatory nitrate reduction lead to? (products)

Answer 7

Can lead to:

• N2 or N2O via denitrification
• NH4+ via dissimilatory nitrate reduction to ammonia (DNRA) a form of ammonification
• both processes

Question 8

True or False. Dissimilatory nitrate reductase is inhibited by NH4+

Answer 8

False

Cells need to continue anaerobic respiration even in the presence of rising NH4+.

• End product inhibition is absent

Question 9

What is DNRA?

Answer 9

Dissimilatory nitrate reduction to ammonia

Type of ammonification (dissimilatory nitrate reduction, followed by nitrite ammonification)

Commonly occurs in (polluted/eutrophic) water with a high [NO3-] and high concentrations of organic compounds

Occurs under AEROBIC and ANAEROBIC conditions (SOIL AND WATER)

Also occurs in marine oxygen minimal zones

Question 10

How is the reaction of conversion of NO3- => N2O called?

Answer 10

Denitrification

Conversion of NO3- => => N2O or N2 gas

• Happens in SOIL and WATER (fresh and marine )

Question 11

What are organisms that are denitrification specialists?

Answer 11

• Paracoccus denitrificans

- Thoibacillus denitrificans

Question 12

What organisms can do facultuative denitrification under anaerobic conditions ? (like flooding..)

Answer 12

• Rhizobium
• Pseudomonas
• Alcaligenes

Question 13

Go to slide 127, draw the graph of aerobic vs anaerobic and the ammonification, nitrification and denitrification reactions

Answer 13

go!

Question 14

What is the N2-fixation reaction catalyzed by the enzyme nitrogenase?

Answer 14

N2 + 8H+ + 8e- => 2NH3 + H2

requires A LOT of energy (approx 24 ATP) and reducing power

Question 15

The majority of biologically available N comes from what process?

Answer 15

Biological N2 fixation (BNF)

Question 16

What are abiotic N2-fixation methods?

Answer 16

• Electrical storms
• Combustion
• Fertilizer manufacture

Question 17

What is the technique to make fertilzier?

Answer 17

Haber-Bosch process

Question 18

What is the Haber-Bosch process?

Answer 18

• High temperature and pressure
• 1.5 kg fuel oil per kg fertilzier manufactured and delivered
• Results in air and water pollution
• Up to 50% applied N fertilizer lost to leaching

Question 19

What are the highest source of N2 fixation?

Answer 19

Legumes and forests

Question 20

What are properties of nitrogenase?

Answer 20

• Very sensitive to irreversible inactivation by O2
• Requires a great deal of energy and reducing equivalents
  - Requires a continuous supply of ATP
  - Requires a continuous supply of electrons (via NADH for ex)

Question 21

Nitrogenase is encoded by what genes?

Answer 21

• nifH, nifD, nifK genes
• Expression of nif genes is HIGHLY REGULATED due to its ENERGY REQUIREMENT (the great expense of N2-fixation ) and SENSITIVITY
• Nif genes expression is reglated by a number of 2-component regulatory systems (sensor-regulator)