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BMB final > Nitrogen Metabolism > Flashcards

Nitrogen Metabolism Flashcards

1
Q

what step begins nitrogen incorporation?

A

fixation to form ammonium (NH3)

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2
Q

How is nitrogen assimilated?

A

It is converted into the amide group of glutamine which can then be used for other carbon-containing compounds

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3
Q

Define symbiotic bacteria

A

has a relationship with another organism in which both organisms benefit

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4
Q

__ N2 + __ ATP –> __ NH3

A

1, 16, 2

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5
Q

what do all species that can fix nitrogen contain?

A

nitrogenase complex

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6
Q

What does the nitrogenase complex consist of?

A

dinitrogenase & dinitrogenase reductase

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7
Q

Dinitrogenase ( ___ protein)

A

MoFe

catalyzes the reaction: N2 + 8H+ + 8e- –> 2NH3 + H2

uses P cluster and MoFe cluster prosthetic groups

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8
Q

Dinitrogenase Reductase ( __ protein)

A

Fe

passes electrons from NAD(P)H one at a time to dinitrogenase

uses 4Fe-4S clusters and MgATP-binding site

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9
Q

First step of nitrogen fixation?

A

transfer of e- from NAD(P)H to ferrodoxin

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10
Q

movement of electrons in nitrogen fixation

A

NAD(PH) -> ferrodoxin -> Fe protein -> Fe protein FeS cluster -> MoFe protein (last step required MgATP hydrolysis)

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11
Q

How many total e- are needed to reduce N2 to NH3?

A

8

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12
Q

Nitrogen Assimilation

A

incorporation of inorganic nitrogen compounds into organic molecules

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13
Q

Glutamine Synthetase

A

catalyzes the ATP-dependent reaction of glutamate with NH4+ to form glutamine

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14
Q

glutamate + NH4 –>

A

glutamine

requires glutamine synthetase catalyst

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15
Q

amino acid pool

A

refers to the organism’s readily available amino acids

constantly changing due to the metabolic state of the cell

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16
Q

Positive nitrogen balance

A

intake exceeds loss

common in children

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17
Q

negative nitrogen balance

A

cannot replace nitrogen loss from dietary sources

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18
Q

Kwashiorkor Malnutrition

A

results of negative nitrogen balance

swollen abdomen

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19
Q

Transamination

A

aminotransferases that are responsible for the reaction are found in the cytoplasm and mitochondria

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20
Q

Two types of specificity for transamination

A
  1. type of a-amino acid that donates the a-amino group

2. a-keto acid that accepts the a-amino group

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21
Q

Transamination pairs

A

pyruvate accepts amino group from glutamate and becomes alanine

glutamate donates its amino group and becomes glutamine

pyruvate = alanine
glutamate = glutamine
22
Q

Two principle means by which ammonium ions are incorporated into amino acids

A
  1. reductive amination of a-keto acids

2. formation of glutamine

23
Q

reductive amination pairs

A

a-ketoglutarate and glutamate

24
Q

Glutamate + NH4+ –> ____

A

glutamine (amide of glutamate)

25
Q

Ubiquitin Proteosomal System (UPS)

A

degrades proteins; mediated by covalent modification

ships out proteins that you don’t need at the time

26
Q

features of proteins marked for destruction by UPS:

A
  1. N-terminal residues often basic or bulky
  2. Peptide Motifs (PEST) indicate small half life
  3. Oxidized residues (oxidized amino acids)
27
Q

PEST

A

peptide motifs; indicate a short half life

28
Q

Proteosomes

A

massive proteolytic machines that ubiquitinated proteins are transferred to

29
Q

ubiquitination

A

attachment of small highly conserved 76-residue protein ubiquitin

occurs in several stages mediated by three enzymes

30
Q

E1 of ubiquitination

A

Ubiquitin-activating enzyme

activates the ubiquitin via adenylation

31
Q

E2 of ubiquitination

A

Ubiquitin-Conjugating enzyme

ubiquitin is transferred to an active thiol site of E2

32
Q

E3 of Ubiquitination

A

Ubiquitin ligase enzyme

binds to E2 and target protein
transfers UQ to a specific internal lysin of the target protein. must transfer at least 4 to ship the protein to a proteosome for degradation.

33
Q

Three steps of amino acid catabolism

A
  1. deamination
  2. urea synthesis
  3. conversion of C skeleton to one of the six metabolic intermediates
34
Q

Deamination

A

removal of the a-amino group from amino acids involves two types of reactions:

  • transamination
  • oxidative deamination
35
Q

transamination reaction

A

a-ketoglutarate + amino acid -> glutamate + a-keto acid

36
Q

alanine

A

carries excess NH4+ to the liver

37
Q

two reactions of alanine carrying NH4 to liver

A

Glu + H2O -> a-KG + NH4+ (glutamine is reduced)
-NAD+ converted to NADH + H+

NH4+ + Glu -> Gln -> blood -> liver
- ATP to ADP+Pi

38
Q

Why does glutamate NOT carry nitrogen to the liver?

A
  • it is a neurotransmitter in the brain

- if levels are elevated it could cause brain to short circuit

39
Q

transamination reaction of alanine

A

Alanine + aKG pyruvate + Glutamate

40
Q

Oxidative deamination reaction

A

Glu + H2O aKG + NH4+

41
Q

Urea Synthesis

A

urea cycle disposes of approximately 90% surplus nitrogen

42
Q

overall equation for urea synthesis

A

CO2 + NH4 + aspartate + 3ATP + 2H2O -> urea + fumarate + 2ADP +2Pi + AMP + PPi + 5H+

43
Q

what begins the process of urea synthesis

A

the formation of a carbomyl phosphate

44
Q

carmobyl phosphate reactions with ____ to form ___

A

ornithine

citrulline

45
Q

Citrullin is transported to ____ where it reacts with ____ to form

A

cytoplasm
aspartate
argininosuccinate

46
Q

argininosuccinate is cleaved by ____ to form ____+____

A

lyase enzyme

arginine & fumarate

47
Q

Arginase enzyme hydrolyzes ___ to form ___ & ____

A

arginine

ornithine & urea

48
Q

urea is transported to _____ for excretion

A

the kidneys

49
Q

Complete process of urea synthesis and extortion (7 steps)

A
  1. formation of a carbomyl phosphate
  2. carbomyl phosphate + ornithine –> citrulline
  3. citrulline is transported to the cytoplase
  4. citrulline + aspartate –> argininosuccinate
  5. argininosuccinate is cleaved by lyase to form argining and fumarate
  6. arginase enzyme hydrolyzes arginine to form ornithine and urea
  7. urea is transported to the kidneys for excretion
50
Q

relationship between urea cycle and citric acid cycle

A

Krebs Bicycle

  • fumarate is produced by urea cycle and feeds into the citric acid cycle to form energy
  • oxaloacetate is an intermediate in citric acid cycle -> can be converted to aspartate, which is needed in urea cycle
51
Q

a-amino acids can be categorized based on ____

A

the products that they form

BMB final (5 decks)

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