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MicroEco > Lecture 17 - Nitrogen Cycling > Flashcards

Lecture 17 - Nitrogen Cycling Flashcards

1
Q

What is the nitrogen cycle?

A

the change in the chemical form nitrogen is present

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2
Q

What nitrogen-based compound is a greenhouse gas?

A

nitrous oxide = can diffuse through membrane

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3
Q

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

A

atmosphere ; 78%

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4
Q

What reservoir of nitrogen is not actively cycled and why?

A

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

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5
Q

Where are the actively recycled forms of nitrogen found?

A

ocean and land

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6
Q

What are the 5 processes of the nitrogen cycle?

A

nitrogen fixation | ammonium assimilation | nitrification | anammox | denitrification

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7
Q

What is the process of nitrogen fixation?

A

N2 gas from sky&raquo_space;> fix into ammonia

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8
Q

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

A

ammonia (NH3)

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9
Q

Which microbes convert nitrogen gas into ammonia?

A

nitrogen-fixing microbes (ie: cyanobacteria)

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10
Q

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

A

aerobic environments

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11
Q

What are diazotrophs?

A

organism capable of fixing nitrogen

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12
Q

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

A

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

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13
Q

What is the nitrogen fixation process inhibited by? Why?

A

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

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14
Q

What is the enzyme that catalyzes the nitrogen fixation process?

A

nitrogenase

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15
Q

What are characteristics of nitrogenase?

A

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

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16
Q

What is dehydrogenase reductase?

A

an iron-protein = need iron as cofactor

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17
Q

What is dinitrogenase?

A

shuttling of electrons between the two protein complex

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18
Q

What are the genes called that encode for nitrogenase?

A

MIF = found on an operon within nitrogen fixers

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19
Q

What occurs when nitrogenase comes into contact with oxygen?

A

nitrogenase is damaged

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20
Q

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

A

heterocyst formation | time and spatial separation | respiration | avoidance

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21
Q

What is the heterocyst formation strategy nitrogen fixers use?

A

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

22
Q

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

A

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

23
Q

What is the respiration strategy nitrogen fixers use?

A

high rates of respiration = chugging oxygen very quickly

24
Q

What is the avoidance strategy nitrogen fixers use?

A

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

25
Q

What are the limits of nitrogen fixation?

A

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

26
Q

What do the limits of nitrogen fixation depend on?

A

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

27
Q

What is ammonia assimilation?

A

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

28
Q

What are the 2 pathways of ammonia assimilation?

A

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

29
Q

Why is the ammonia assimilation process important for diazotrophs?

A

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

30
Q

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

A

NH4 ammonia | ocean

31
Q

What is the nitrification process?

A

microbially catalyzed conversion of ammonium into nitrate

32
Q

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

A

nitrate

33
Q

Where does nitrate come from?

A

all of the ammonia

34
Q

What microbes are capable of oxidizing NH4 into NO3?

A

none

35
Q

What are the 2 steps of nitrification?

A

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

36
Q

What is AOB?

A

ammonia oxidizing bacteria = proteobacteria

37
Q

What do AOB rely on as an energy source?

A

ammonia

38
Q

What enzyme does AOB use?

A

ammonia monooxygenase = amor gene

39
Q

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

A

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

40
Q

What does Anammox stand for?

A

anaerobic ammonia oxidation

41
Q

What is anammox?

A

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

42
Q

How was anammox discovered?

A

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

43
Q

What is an ammoxosome?

A

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

44
Q

What is denitrification process?

A

NO3&raquo_space;> N2 or N2O | series of reduction steps

45
Q

What are the 4 enzymes in denitrification?

A

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

46
Q

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

A

oxygen = denitrification happens primarily in anoxic environments

47
Q

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

A

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

48
Q

What is nitrous oxide?

A

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

49
Q

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

A

270x

50
Q

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

A

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

51
Q

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

A

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

52
Q

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

A

anammox | ammonia oxidation | nitrite oxidation

MicroEco (10 decks)

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