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MCB 2 Block 3 > Nitrogen > Flashcards

Flashcards in Nitrogen Deck (22):

Transamination Info

Process of removing one NH3 from one amino acid and put on another with creation of alpha keto acid.

Cofactor = PLP (Vit B6); schiff base: enzyme's Lys episilon - NH2 binds to carbon of PLP aldehyde group -> DBond


Transamination usual

Glu, Ala, Asp usually used. Glu to alpha-ketoglutarate, Ala to pyruvate, Asp to OAA

Reversible and active in liver, Liver dmg look for ALT and AST.

AA1 and a-keto2 to AA2 and a-keto1



Release free NH3.

Enzyme = Glutamate Dehydrogenase (Glu is only AA that accepts free NH2)

Glu =(NADh and Nh3) a-ketoglutarate

NADH = ATP synth; NADPH = biosynth


Toxic NH3

needs to be removed
number 1 source = Gln; enzyme = glutaminase
removed via urea cycle


Step 1 Urea cycle

In mito
Free NH3 and HCO3 to carbomyl phosphate
Enz= carbomyl phosphate synthase 1, rqrs 2 ATP
Allosteric activation by N-acetyl-glutamate (act by Arg)


Step 2 Urea Cycle

Carbomyl phosphate and Ornithine to Citrulline
Enz = Ornithine Transcarbomylase (OTC)


OTC def

Hyperammonemia, Orotic acid build up, loss of ATP (due to diversion of alpha ketoglutarate from TCA cycle in order to soak up NH3, Glu to Gln via glutamine synthetase requires ATP so more lost)


Step 3 Urea cycle

Citrulline leaves mito to cytosol
Citrulline and Asp to Arginosuccinate
Asp provides second NH3
Enz = Arginosuccinate synthetase, rqrs ATP


Urea Cycle energy rqr

4 ATP equivalents


Urea Cycle Step 4

Arginosuccinate to Arg and Fumarate
Enzyme = arginosuccinate lyase
Some Arg used for feedback to CPS1, Fumarate to TCA cycle via conversion to malate


Urea cycle Step 5

Arg to Ornithine and Urea
Enz = Arginase
urea to urine, ornithine to mito for reuse



Liver dmg = decreased BUN
Kidney dmg = increased BUN
Tx = alternate N extract = Benzoic acid, phenylacetate, phenylbutyrate. Conjugates with gly and gln to make H20 soluble


Draw Urea Cycle

On paper


Nitrogen after meal stomach

pepsin breaks up some proteins to AA


Nitrogen after meal SI

Trypsin, chymotrypsin, elastase, carboxy peptides A and B finish job. Breaks to AA or di/tripeptide AA


Nitrogen after meal to blood

Via Sodium dependent transporters.
Exception = BCAA and Aromatic AA (all essential so absorbed asap)


Nitrogen after meal Liver disperse

To musc for build: BCAAs to M for energy catabolism

Stay in liver for energy production via gluconeogenesis and plasma proteins

Kidney for excretion


AA's during fast

Ala and Gln will go back to liver for energy prod via gluconeo, this removes NH2 (to urea cycle)


Protein Degrade

Determined by half life
shortest = PEST (Pro, Glu, Ser, Thr)
methods = ubiquitin proteosome and Calpain (Calcium dependent self destruction)


N balance

Pos = NH3 in > loss for growth and preg
Neg = NH3 in < loss for trauma, cancer, starve


AA's as energy

All are glucogenic except Leu and Lys = ketogenic
AA's both gluc and keto = Aromatics (Tyr, Phe, Trp) and Ile


Diet Induced Thermogenesis

Specific Dynamic action - energy required to break down substrate (prot>fat>carbs)

Resp Quotient: amt CO2 prd/ O2 cons, more carbs = higher RQ. C=1, fats = .66, prots = .8)