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BIOL 241 > N,S cycling > Flashcards

N,S cycling Flashcards

1
Q

assimilative reactions - give example

A

nutrients are incorporated into the biomass of an organism - assimilatory NO3 reduction –> NH4, requires assimilatory nitrate reductase

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2
Q

T/F - nitrate reductase is only single enzyme

A

false - nitrate reductaste can be assimilatory or dissimilatory

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3
Q

dissimilative reactions

A

when compounds are reduces as terminal e acceptors in energy metabolism - dissimilatory NO3 reduction —>N2
requires dissimlatory nitrate reductase

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4
Q

denitrification

A

dissimilatory reaction, oxidized N compounds is e acceptor in energy metabolism

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5
Q

what is oxygen requirements of denitrifiers

A

most are facultative aerobes - prefer to use o2

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6
Q

where do most denitrfication reactions happen

A

anoxic environments

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7
Q

is e. coli a denitrify?

A

no - it can do the first step (nitrate to nitrite), but can’t do the rest

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8
Q

what are all the steps of denitrificaitions

A

no3 –> no2 –> NO –> N2O –> N2

last 3 are gasses

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9
Q

what are the practical imlications of N cycle rxns

A 
n2 fixation
ammonifixation
nitrification
denitrification
agriculture practices
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10
Q

n2 fixation

A

converts unusable n2 to combined N (eg. ammonia)

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11
Q

ammonification pros and cons

A

releases NH4+ for subsequent use in new biomass [good]
NH4+ is most efficient form of inorganic N for incorporation
NH4 is cationic, thus held in soil (clay) [good]
some NH3 loss from soilt o atmosphere [bad]

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12
Q

NH4+ positives

A

hangs out in soil surface, and when it rains, it won’t get washed down below root zone

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13
Q

empirical formula for biomass

A

C106H263O110N16P

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14
Q

true/false - atmosphere is a major reservoir for nitrogen

A

true, 80% nitrogen but this isn’t usable by most organisms

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15
Q

n2 fixation

A

conducted by relatively few prokaryotes that use nitrogenase complex (enzyme)
vital to life
makes nitrogen more readily usable
N2 –> NH3 + H2

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16
Q

what is the oxidation state of organic N, ammonia, nitrogen gas, and nitrate?

A

-3, -3, 0, +5

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17
Q

what are the major steps in the biotic nitrogen cycle?

A 
N2 fixation
mineralization
anammox
assimilation
nitrification
denitrification
18
Q

PICTURE

A

picture answer

19
Q

nitrification

A

NH4+ + 2H2O –> NO2- + 8H+ + 6e-
NO2- + 2H2O –> NO3- + 2H+ + 2e-
nitrosomonas
nitrobacter

20
Q

denitrification

A

NO3- –> N2

bacillus, parcoccus, pseudomonas

21
Q

types of nitrogen redox reactions listen by # of prokaryotes who perform the reaction (most to least)

A

n2 fixation > denitrification > nitrification > ammonification

22
Q

nitrogenase complex function and feature

A

n2 fixation
o2 sensitive and subject to strict regulatory control by combined N
N2 + 8H+ + 8e- –> 2NH3 + H2

23
Q

what is the site of reduction for dihydrogenase

A

FeMo-co

24
Q

examples of nitrogen-fixing microorganisms

A

symbiotic (mutualisms)
free-living aerobes
free-living anaerobes

25
Q

examples of symbiotic nitrogen-fixing microorganisms

A

legume-rhizobia symbioses - soybeans, clover, alfalfa with rhizobial bacterium, and actinorhizal plants like alder trees

26
Q

examples of free-living nitrogen-fixing aerobes

A

chemoorganotrophs including Azotobacter, klebsiella, methylcoccus, and other phototrophs: many cyanobacteria, chemolithotrophs: alcaligenes, some thiobacillus and others

27
Q

examples of free-living nitrogen-fixing anaerobes

A

chemoorganotrophs inlcuding clostridium, desulfovibrio and phototrophs including chromacium, thiocapsa, chlorobium, rhodospirillium, and chemolithotrophs - methanosarcina, methanococcus and other methanogens

28
Q

heterocyst

A

modified cells found in certain filamentous cyanobacteria

lack photostem II (and thus do not produce O2) but possess nitrogenase and can conduct N2

29
Q

symbiotic n2 fixation - steps in the formation of a root nodule in a legume infected by rhizobium

A
  1. bacterium attaches to root hair
  2. root hair curls around bacterium forming shepherd’s crook
  3. infection thread forms and bacteria replicates
  4. infection thread extends into root cortex as root cells divide
  5. infection thread branches, bacteria enter cell walls, lose their cell walls, and become n2-fixing bacteria
  6. nodule consisting of plant cells is stimulated to grow by infecting bacteroids
30
Q

flavanoid

A

class of plant and fungus secondary metabolites

31
Q

how is root curling induced by rhizobium in n2 fixation

A

plant excretes flavanoids, attracting rhizobia, incuding nod factor synthesis
bacterial signalling molecules (nod factors) control nodule formation (eg root cell formation)

32
Q

what is the major carbon compound metabolized by bacteria as they fix nitrogen?

A

C4 dicarboxylic acids (succinate, fumarate, malate)

33
Q

bacteroids

A

rhizobial cells transformed into swollen, misshapen branched shapes within the plant cell, possess nitrogenase activity, incapable of cell division

34
Q

symbiosome

A

single or small groups of bacteroids surrounded by portions of plant cell membrane
n2 fixation begins after symbiosome formation

35
Q

leghemoglobin

A

o2-binding protien
supplies o2 to bacteroid and protects nigtrogenase from o2 inactivation
synthesis requires input from the plant and the bacterium
Lb delivers bound O2 directly to bacterial ETS, protects nitrogenase complex from O2 damage

36
Q

how does the exchange of C and N compounds between bacteria and plants work?

A

C4-dicarbozylic acids are taken up by bacteroids in plant cytoplasm to enter into TCA cycle to make ATP, then the ATP and electrons that are generated are used by nitrogenase to convert nitrogen gas into ammonia (nitrogen fixation), ammonia is then used by bacteroids to make amino acids
excess ammonia used by plants to make ammonium

37
Q

ammonification

A

RNH2 –> NH3 (NH4+)
production of ammonia during the decomposition of organic nitrogen compounds
conducted by wide range of aerobes, anaerobes

38
Q

what is ammonification like in oxic conditions?

A

some NH3 volatilization to atmosphere (favoured by dark, alkaline soil)
assimilation by plants, microorganisms, production of new biomass
NH4 subjected to nitrification

39
Q

what is ammonification like in anoxic conditions?

A

NH4+ tends to be stable and persist (exception anammox - anoxic ammonia oxidation; occurs in some ammonia rich habitats such as sewage)

40
Q

what environment conditions are good for nitrification?

A

well-drained, neutral-pH soils, aquatic environment

41
Q

what type of metabolism should a microbe have for nitrification?

A

aerobic, chemolithotrophic

BIOL 241 (5 decks)

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