Lecture 17 - Nitrogen Cycling

Question 1

What is the nitrogen cycle?

Answer 1

the change in the chemical form nitrogen is present

Question 2

What nitrogen-based compound is a greenhouse gas?

Answer 2

nitrous oxide = can diffuse through membrane

Question 3

What is the largest reservoir of nitrogen? What percent of nitrogen makes up this reservoir?

Answer 3

atmosphere ; 78%

Question 4

What reservoir of nitrogen is not actively cycled and why?

Answer 4

atmosphere, most organisms cannot utilize this form of nitrogen (N2)

Question 5

Where are the actively recycled forms of nitrogen found?

Answer 5

ocean and land

Question 6

What are the 5 processes of the nitrogen cycle?

Answer 6

nitrogen fixation | ammonium assimilation | nitrification | anammox | denitrification

Question 7

What is the process of nitrogen fixation?

Answer 7

N2 gas from sky&raquo_space;> fix into ammonia

Question 8

What is the form of nitrogen that most/all microbes can use?

Answer 8

ammonia (NH3)

Question 9

Which microbes convert nitrogen gas into ammonia?

Answer 9

nitrogen-fixing microbes (ie: cyanobacteria)

Question 10

Which type of environment (aerobic or anaerobic) does nitrogen fixation commonly occur in?

Answer 10

aerobic environments

Question 11

What are diazotrophs?

Answer 11

organism capable of fixing nitrogen

Question 12

Why is the nitrogen-fixing process an energy-intensive reaction?

Answer 12

need 16 ATPs to make 2 ammonia because it is hard to break the triple bonds between N in N2

Question 13

What is the nitrogen fixation process inhibited by? Why?

Answer 13

high concentrations of ammonia = cells don’t want to spend more energy making more ammonia when there is already a lot

Question 14

What is the enzyme that catalyzes the nitrogen fixation process?

Answer 14

nitrogenase

Question 15

What are characteristics of nitrogenase?

Answer 15

oxygen-sensitive | complex of 2 proteins: dehydrogenase reductase and dinitrogenase

Question 16

What is dehydrogenase reductase?

Answer 16

an iron-protein = need iron as cofactor

Question 17

What is dinitrogenase?

Answer 17

shuttling of electrons between the two protein complex

Question 18

What are the genes called that encode for nitrogenase?

Answer 18

MIF = found on an operon within nitrogen fixers

Question 19

What occurs when nitrogenase comes into contact with oxygen?

Answer 19

nitrogenase is damaged

Question 20

What are the 4 strategies that make nitrogen fixers capable of fixing nitrogen when oxygen is toxic to nitrogenase?

Answer 20

heterocyst formation | time and spatial separation | respiration | avoidance

Question 21

What is the heterocyst formation strategy nitrogen fixers use?

Answer 21

specialized cells with a thicker cell wall where they sequester the nitrogen-fixing components they need such as nitrogenase | not much photosynthesis occurring in these cells | photosynthesis and nitrogen-fixation are separated within bacteria

Question 22

What is the time-and-spatial separation strategy nitrogen fixers use?

Answer 22

separate by time = doing things at different times ; spatial = separate by area

Question 23

What is the respiration strategy nitrogen fixers use?

Answer 23

high rates of respiration = chugging oxygen very quickly

Question 24

What is the avoidance strategy nitrogen fixers use?

Answer 24

such as proteins that bind to oxygen to prevent it from binding to nitrogenase

Question 25

What are the limits of nitrogen fixation?

Answer 25

needs hella ATP | light and carbon compounds | amount of NH3 | iron and Mo | oxygen

Question 26

What do the limits of nitrogen fixation depend on?

Answer 26

environment ie: ocean = low iron = low levels of nitrogen fixation

Question 27

What is ammonia assimilation?

Answer 27

moving NH3 into a form that cells can use such as amino acids

Question 28

What are the 2 pathways of ammonia assimilation?

Answer 28

Low NH4 = glutamine synthetase (GS) | High NH4 = glutamine dehydrogenase (GDH)

Question 29

Why is the ammonia assimilation process important for diazotrophs?

Answer 29

to ensure the nascent NH3 doesn't inhibit further N2 fixation = wanna keep N2-fixing going

Question 30

What is nitrogen primarily cycled as? And mostly in what environment?

Answer 30

NH4 ammonia | ocean

Question 31

What is the nitrification process?

Answer 31

microbially catalyzed conversion of ammonium into nitrate

Question 32

What is the largest reservoirs for nitrogen? (what is it in the form of)

Answer 32

nitrate

Question 33

Where does nitrate come from?

Answer 33

all of the ammonia

Question 34

What microbes are capable of oxidizing NH4 into NO3?

Answer 34

none

Question 35

What are the 2 steps of nitrification?

Answer 35

ammonia oxidation (NH4 >>> NO2) | nitrite oxidation (NO2 >> NO3) | BOTH are aerobic processes

Question 36

What is AOB?

Answer 36

ammonia oxidizing bacteria = proteobacteria

Question 37

What do AOB rely on as an energy source?

Answer 37

ammonia

Question 38

What enzyme does AOB use?

Answer 38

ammonia monooxygenase = amor gene

Question 39

What is the rate-limiting step within the nitrification process? How were scientists able to prove this was the rate limiting step?

Answer 39

ammonia oxidation | NO2 was rarely seen in the environment = means it was used ASAP

Question 40

What does Anammox stand for?

Answer 40

anaerobic ammonia oxidation

Question 41

What is anammox?

Answer 41

organisms capable of nitrification anaerobically | takes ammonium NH4 and nitrite NO2 and bypassing the rest of the cycle to get N2 gas

Question 42

How was anammox discovered?

Answer 42

if ammonia oxidation can't happen in anaerobic environments = expect to see a high concentration of it but you don't == theorize that anaerobic bacteria use up the NH4 via anammox

Question 43

What is an ammoxosome?

Answer 43

an "organelle" = vesicle-like structure in bacteria where ammonia oxidation occurs | similar to mitochondria

Question 44

What is denitrification process?

Answer 44

NO3 >>> N2 or N2O | series of reduction steps

Question 45

What are the 4 enzymes in denitrification?

Answer 45

nitrate (NO3) reductase | nitrite (NO2) reductase | nitric oxide (NO) reductase | nitrous oxide (N2O) reductase

Question 46

What are the 4 enzymes in denitrification sensitive to? What does this mean?

Answer 46

oxygen = denitrification happens primarily in anoxic environments

Question 47

What 2 processes in the nitrogen cycle are coupled? Why or How?

Answer 47

nitrification and denitrification | product of nitrification = nitrate = source/starting point of denitrification

Question 48

What is nitrous oxide?

Answer 48

destroys ozone very readily | can be released via burning fossil fuels

Question 49

How many times more efficient is nitrous oxide at trapping heat compared to CO2?

Answer 49

270x

Question 50

What is the biggest contributor to atmospheric nitrous oxide? Why?

Answer 50

fertilizer (agriculture) = when it is added = you're adding ammonia = catalyzes whole nitrogen cycle and stimulates production of N2O

Question 51

Which process(es) in the nitrogen cycle produces nitrous oxide?

Answer 51

denitrification | can be produced as a by-product of nitrification

Question 52

In the nitrification reaction, which steps/parts produces N2O as a byproduct?

Answer 52

anammox | ammonia oxidation | nitrite oxidation