Chapter 18 Flashcards
What converts N2 –> NH3
also NH3 –> NH4+
Nitrogenase
Nitrogen fixing organisms
Diazotrophs: Marine cyanobacteria/root nodule bacteria that make nitrogenase
Biological productivity is limited by …
availability of fixed N₂
Nitrogenase structure
Iron-sulfur centers
Cofactor with both iron and molybdenum (FeMo)
needs 8e-
consumes 16 ATP
FeMo cofactor: What does it do?
Facilitates breaking through triple bonds in N, requires strong reducing agents such as donor (ferredoxin). Consumes ATP. Needs 8e-
What inactivates nitrogenase
Oxygen
Oxidation of NH4+ –> NO3-
Nitrification (Nitrogen reductase)
Conversion of NO3- to N2
Denitrification
GluatMINE synthEtase
Microorganisms: entry point for fixed nitrogen
Animals: absorbs excess ammonia, which is toxic
Step 1: ATP donates phosphoryl group to glutamate
Step 2: Ammonia reacts with intermediate, displacing Pi to make glutamine
ATP consumed
Glu/Gln = amino group carriers (in high concentration)
Activity tightly regulated to maintain supply of amino groups
____ assimilates fixed nitrogen as NH₄+ into organic compound (CAC intermediate) to make amino acid
Combination of Gln synthetase and glu synthase
Glutamate synthase
Exchange amine group
Transfer 2nd NH2 to alpha ketoglutarate
Creates 2 glutamates
How do amino acids move between compounds?
Transaminase
Only amino acid that can’t be transaminated?
Lysine
Most transaminases only accept __________________ as the alpha-keto acid substrate
alpha-ketoglutarate or oxaloacetate
What is the acid/base catalyst in transaminase?
Enzyme Lys, acts as schiff
Transaminase cofactors
Requires PLP prosthetic group for transient attachment
Derivative of pyridoxine (Vitamin B₆)
Covalently attached to enzyme via schiff base (imine) linkage to Lys residue
Nonessential (define)
we make it
Essential (define)
we need to eat it
Nonessential (list)
A’s, G’s,
Promote, Serious, Roses
(proline, serine, tyrosine)
Essential (list)
HILL
MVP
There’s 9 Tries
Branched Essentials from pyruvate – >
Valine, Isoleucine, Leucine
Val, Ile, Leu (VIL)
Aspartate Essentials – >
Already have head group
Lysine, Methionine, Threonine
(LET ME THRive to what I ASPire)
Lys, Met, Thr (K, M, T)
PEP + Erythrose-4-phosphate –> Chorismate
Condensation C3/C4
Essential
Phenylalanine, Tryptophan
Phe, Trp
F, W
ATP + glu and gln + PRPP
Essential
ATP provides 1 N and 1 C
Glutamate/Glutamine donate other 2 N
PRPP gives other 5 C
Histidine
His, H
Name the 3 nonessential transamination
1) Pyruvate –> Alanine
2) Oxaloacetate –> AsparatATE (asp)
3) Alpha-Ketoglutarate –> GlutamATE (glu)
What 3 nonessentials can glutamate make?
Arginine, Glutamine, Proline
Glutamine + Aspartate (nonessential)
Asparagine (+ glutamate)
3-phosphoglycerate (glycolytic intermediate)
nonessential
Serine
Serine (nonessential precursor to what)
glycine
Methionine/Homocystine thing
nonessential precursor
Cysteine
Phenylalanine (Chrisimate)
Tyrosine
Signaling Molecules precursors
Tyrosine → Dopamine, Norepinephrine, and Epinephrine
Tryptophan → Serotonin → Melatonin
Arginine → Nitric Oxide
When are amino acids partially oxidized substrates for gluconeogenesis or ketogenesis
During fast when not enough oxygen available for the liver to completely oxidize all carbon to CO2.
Glucogenic-
The large skeletons of aromatic amino acids are both glucogenic and ketogenic
giving rise to gluconeogenic precursors such as CAC intermediates
Most nonessential
Ketogenic
giving rise to acetyl-CoA which can be used for ketogenesis or fatty acid synthesis, but not gluconeogenesis
Only two ketogenically exclusive amino acids
Leucine and Lysine
Which are both ketogenic and glucogenic?
All t’s
Isoleucine
Phenylalanine
Aromatic rings
Glucogenic: only makes succinyl-CoA?
Methionine and Valine
Glucogenic: only makes pyruvate
Alanine, Serine, Cysteine
Glucogenic Only:
Aspartate –> oxaloacetate
Aspartate (duh)
Asparagine
Glucogenic only: Glutamate –> Alpha-ketoglutarate
Arginine Glutamate Glutamine Histidine Proline
Glucogenic only: Glycine thing
Glycine –> Co2
Glycine cleave system, multicomplex enzyme with tetrahydrofolate
Isoleucine –>
Threonine –>
Iso: Succinyl-CoA and acetyl-CoA
Threonine: glycine and acetyl-CoA
Leucine/Lysine –>
acetyl-CoA and acetoacetate
Phenylalanine/Tryptophan/Tyrosine –>
acetoacetate and either fumarate or pyruvate
Uses cofactors tetrahydrobiopterin. Like folate contains pterin group
Two entry points for aminos into urea cycle
Glutamate in mitochondria
Cytosol as aspartate
major site of glutamine catabolism
Kidney
___ supplies nitrogen to urea cycle
glutamate,
What is the primary regulatory step for generation of entry point in urea cycle?
Carbamoyl phosphate synthetase reaction
Urea cycle uses __ to activate bicarbonate unit
ATP
What is the regulator of carbamoyl phosphate synthetase reaction?
N-acetyl-glutamate
Inherent metabolic sensor
How do you increase flux in urea cycle?
Increase intermediates by carbamoyl phosphate synthetase
Cost of Urea cycle
4 ATP per Urea