Nitrogen Metabolism Flashcards
what step begins nitrogen incorporation?
fixation to form ammonium (NH3)
How is nitrogen assimilated?
It is converted into the amide group of glutamine which can then be used for other carbon-containing compounds
Define symbiotic bacteria
has a relationship with another organism in which both organisms benefit
__ N2 + __ ATP –> __ NH3
1, 16, 2
what do all species that can fix nitrogen contain?
nitrogenase complex
What does the nitrogenase complex consist of?
dinitrogenase & dinitrogenase reductase
Dinitrogenase ( ___ protein)
MoFe
catalyzes the reaction: N2 + 8H+ + 8e- –> 2NH3 + H2
uses P cluster and MoFe cluster prosthetic groups
Dinitrogenase Reductase ( __ protein)
Fe
passes electrons from NAD(P)H one at a time to dinitrogenase
uses 4Fe-4S clusters and MgATP-binding site
First step of nitrogen fixation?
transfer of e- from NAD(P)H to ferrodoxin
movement of electrons in nitrogen fixation
NAD(PH) -> ferrodoxin -> Fe protein -> Fe protein FeS cluster -> MoFe protein (last step required MgATP hydrolysis)
How many total e- are needed to reduce N2 to NH3?
8
Nitrogen Assimilation
incorporation of inorganic nitrogen compounds into organic molecules
Glutamine Synthetase
catalyzes the ATP-dependent reaction of glutamate with NH4+ to form glutamine
glutamate + NH4 –>
glutamine
requires glutamine synthetase catalyst
amino acid pool
refers to the organism’s readily available amino acids
constantly changing due to the metabolic state of the cell
Positive nitrogen balance
intake exceeds loss
common in children
negative nitrogen balance
cannot replace nitrogen loss from dietary sources
Kwashiorkor Malnutrition
results of negative nitrogen balance
swollen abdomen
Transamination
aminotransferases that are responsible for the reaction are found in the cytoplasm and mitochondria
Two types of specificity for transamination
- type of a-amino acid that donates the a-amino group
2. a-keto acid that accepts the a-amino group
Transamination pairs
pyruvate accepts amino group from glutamate and becomes alanine
glutamate donates its amino group and becomes glutamine
pyruvate = alanine glutamate = glutamine
Two principle means by which ammonium ions are incorporated into amino acids
- reductive amination of a-keto acids
2. formation of glutamine
reductive amination pairs
a-ketoglutarate and glutamate
Glutamate + NH4+ –> ____
glutamine (amide of glutamate)
Ubiquitin Proteosomal System (UPS)
degrades proteins; mediated by covalent modification
ships out proteins that you don’t need at the time
features of proteins marked for destruction by UPS:
- N-terminal residues often basic or bulky
- Peptide Motifs (PEST) indicate small half life
- Oxidized residues (oxidized amino acids)
PEST
peptide motifs; indicate a short half life
Proteosomes
massive proteolytic machines that ubiquitinated proteins are transferred to
ubiquitination
attachment of small highly conserved 76-residue protein ubiquitin
occurs in several stages mediated by three enzymes
E1 of ubiquitination
Ubiquitin-activating enzyme
activates the ubiquitin via adenylation
E2 of ubiquitination
Ubiquitin-Conjugating enzyme
ubiquitin is transferred to an active thiol site of E2
E3 of Ubiquitination
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.
Three steps of amino acid catabolism
- deamination
- urea synthesis
- conversion of C skeleton to one of the six metabolic intermediates
Deamination
removal of the a-amino group from amino acids involves two types of reactions:
- transamination
- oxidative deamination
transamination reaction
a-ketoglutarate + amino acid -> glutamate + a-keto acid
alanine
carries excess NH4+ to the liver
two reactions of alanine carrying NH4 to liver
Glu + H2O -> a-KG + NH4+ (glutamine is reduced)
-NAD+ converted to NADH + H+
NH4+ + Glu -> Gln -> blood -> liver
- ATP to ADP+Pi
Why does glutamate NOT carry nitrogen to the liver?
- it is a neurotransmitter in the brain
- if levels are elevated it could cause brain to short circuit
transamination reaction of alanine
Alanine + aKG pyruvate + Glutamate
Oxidative deamination reaction
Glu + H2O aKG + NH4+
Urea Synthesis
urea cycle disposes of approximately 90% surplus nitrogen
overall equation for urea synthesis
CO2 + NH4 + aspartate + 3ATP + 2H2O -> urea + fumarate + 2ADP +2Pi + AMP + PPi + 5H+
what begins the process of urea synthesis
the formation of a carbomyl phosphate
carmobyl phosphate reactions with ____ to form ___
ornithine
citrulline
Citrullin is transported to ____ where it reacts with ____ to form
cytoplasm
aspartate
argininosuccinate
argininosuccinate is cleaved by ____ to form ____+____
lyase enzyme
arginine & fumarate
Arginase enzyme hydrolyzes ___ to form ___ & ____
arginine
ornithine & urea
urea is transported to _____ for excretion
the kidneys
Complete process of urea synthesis and extortion (7 steps)
- formation of a carbomyl phosphate
- carbomyl phosphate + ornithine –> citrulline
- citrulline is transported to the cytoplase
- citrulline + aspartate –> argininosuccinate
- argininosuccinate is cleaved by lyase to form argining and fumarate
- arginase enzyme hydrolyzes arginine to form ornithine and urea
- urea is transported to the kidneys for excretion
relationship between urea cycle and citric acid cycle
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
a-amino acids can be categorized based on ____
the products that they form
