Chapter 18 Flashcards
Nitrogenase carries out the energetically expensive reduction of ____ to ____
N2
NH3
N2 fixation into NH3 happens in the
root nodules of legumes
Ammonia is toxic at high concentrations so it must be
assimilated into useful compounds
The formation of the amino acids, ____ and ____, from ammonia is of central importance in reducing ammonia concentrations and carrying nitrogen around the body
glutamate and glutamine
Glutamate is formed by _____ of ketogluturate
reductive amination
the reductive amination of ketoglutarate to glutamate is catalyzed by
glutamate dehydrogenase
Glutamate is converted to glutamine by _____ via another amidation reaction
glutamine synthetase
Transamination reactions transfer an amino group from one amino acid to an ______ to make a new amino acid
alpha keto acid
Difference between an amino acid and an alpha keto acid
NH2 group for amino
O double bond C in keto acid
Amino groups are donated to precursors via
transamination reactions
Glutamate family in the TCA cycle
alpha-ketoglutarate
glutamate
glutamine
proline
arginine
Aspartate family of the TCA cycle
Oxaloacetate
aspartate
asparagine
methionine
threonine
lysine
isoleucine
Transamination reactions substrates and products
Substrate 1- amine donor
substrate 2- keto acid (amine receiver)
Product 1- alpha keto acid
Product 2- amino acid
The amino acid NH2 donor becomes
an alpha keto acid
Pyridoxal-5’-phosphate is a derivative of
pyridoxine
Serine and one-carbon transfers are catalyzed by
serine hydroxymethyltransferase
tetrahydrofolate is a derivative of _____ and is
folic acid
one-carbon group acceptor in this reaction
Folic acid is a vitamin that
prevents birth defects and may lower risk of stroke
Serine to glycine
serine becomes glycine upon donation of one carbon methylene group
Carbon skeletons can follow
glucogenic or ketogenic pathways depending on the type of end product
Glucogenic amino acids do what
catabolized to pyruvate or oxaloacetate and used to make glucose via gluconeogenesis
ketogenic amino acids are catabolized to ___ and used to make ___
acetyl-CoA or acetoacetyl-CoA
ketone bodies when in excess
Approximately 80% of excess nitrogen is excreted as
urea
Urea is produced in the ___
liver
In the urea cycle nitrogen is used to make _____ which is cleaved to release urea
arginine
Nitrogen is used to make arginine comes from two sources _______
ammonia from oxidative deamination of AA
Aspartate donates amino group
Carbonyl phosphate is an
amino group acceptor/donor
Urea cycle steps
1.ornithine transcarbamoylase produces citrulline by transferring a carbamoyl group
2.argininosuccinate synthetase adds aspartate to citrulline in an ATP-dependent condensation reaction. Products AMP and PPi- which is subsequently hydrolyzed to 2 Pi- consumes 2 ATP equivalents
- Argininsuccinase releases fumarate from argininosuccinate
4.arginase hydrolyzes arginine to generate urea and regenerate ornithine for another round of the urea cycle
Ornithine enters the _____ and accepts amino group from carbamoyl phosphate to make citrulline
mitochondria
Aspartate displaces AMP to form arginosuccinate- this is the ____
second nitrogen source
Arginine is cleaved to form
urea
ornithine
