module 11- amino acid degradation & urea cycle Flashcards
what is the 1st step in amino acid degradation
nitrogen removal
ammonium ion is converted to what in most terrestrial vertebrates?
urea
carbon skeletons of degraded amino acids emerge as?
intermediates
T or F: no storage of amino acids so we need them everyday
T
inputs to amino acid pool
defective cells, dietary protein
T or F: some organisms such as yeast/bacteria can synthesize all 20 amino acids
T
average person requires ( ) of dietary protein per day to maintain amino acid pool
70-100g
proteolysis- what occurs & where does it begin/end
peptide bonds are cleaved, begins in stomach & goes to small intestine
2 purposes of low gastric pH
1) causes denaturation of protein
2) antiseptic- destroys bacteria/viruses
2 components of gastric juice
pepsin & gastrin
pancreatic juice components
bicarbonate & proteases
what does the array of proteases cause?
proteins to be rapidly degraded into free amino acids
where are free amino acids absorbed & where do they go
endothelial cells, portal vein
all of the proteolytic enzymes involved in protein digestion are synthesized as ( ) to protect from self degradation?
inactive zymogens
how are zymogens activated
small portion of polypeptide backbone cut off to change conformation
what triggers removal of masking sequence?
low pH
autocatalysis
self-activation
where are pancreatic proteases stored?
granules
protease self-activation
attack & degrade each other when their activity is not needed
gastroesophageal reflux disease cause
over-active proton pump in the stomach = too much acid production
how do antacids work
act as proton sponges & reduce acidity
what pump is involved in GERD
K/H pump
inhibition of histamine H2 receptor
inhibits histamine = less acid
proton pump inhibitors
bind directly to proton pump & inhibit its ability to pump protons into lumen
excess amino groups are secreted in the form of ( ), while carbon skeletons are converted to ( )
urea, a-keto acids
what are a-keto acids used for
energy production or gluconeogenesis
transamination
amino groups form 1 amino acid
oxidative deamination
amino group from glutamate is released as NH4
transdeaminination
transamination & deamination combined
where does urea production occur
liver
what is the 1st step in amino acid degradation
transamination
what do aminotransferases do?
transfer amino group from a-ketoglutarate to glutamate
what do aminotransferases require as a coenzyme?
pyridoxal phosphate- derived from vitamin B6
the nomenclature for aminotransferases are based on?
amino acid donor
alaine aminotransferase
transfers amino group from alanine to a-ketoglutarate to produce glutamate & pyruvate
aspartate aminotransferase
transfers amino group from aspartate to a-ketoglutarate to produce glutamate & oxaloacetate
T or F: elevated aminotransferases levels can be used to diagnose medical conditions
T
at pH of 7.4, most is in ( ) form
NH4 form
T or F: ammonium is odorless
T
glutamate undergoes oxidative deamination which releases ( ) + ( )
NH4 + a-ketoglutarate
T or F: we have very little free ammonia in our bodies
T
where is free ammonium produced? why?
mitochondria, can be used to form urea which prevents accumulation
glutamate dehydrogenase
removes amino group & oxidation of glutamate
electrons removed from glutamate by glutamate dehydrogenase are captured as?
NADH or NADPH
in most tissues, free ammonium is incorporated into ( ) by ( )
glutamine, glutamine synthetase
T or F: most amino acids cannot get out of cells
T
what amino acid can leave cells
glutamine
glutaminase- location & what does it do
liver, uses water to cleave ammonium off of glutamine
most ammonim gets transported out of the muscle in the form of?
alanine
glucose-alanine cycle
alanine-> glutamate -> pyruvate -> glucose -> pyruvate
contributions to the glutamate pool come from
alanine from muscle & glutamine from tissues
glutamate is acted on by glutamate dehydrogenase to?
releases ammonium
urea is ( ) soluble in water
highly
precursors for urea are?
NH4, CO2 & aspartate
urea cycle
reactions that occur in the mitochondira & the cytosol
where does the urea cycle start? why?
mitochondria, bc ammonia is released here
what is the rate limiting enzyme for urea cycle
carbamoyl phosphate synthetase
carbamoyl phosphate synthetase I- location
mitochondrial matrix
obligate allosteric activator of carbomoyl phosphate synthetase I
N-acetylglutamate
obligate activator
required for its target enzyme to have activity
how is N-acetylglutamate stimulated
presence of arginine
where do the 2 amino groups on urea come from?
free ammonium & aspartate
urea cycle part 2
urea is produced & ornithine is replenished
citrulline is acted upon by ?
argininosuccinate synthetase
when argnine is acted upon by the hydrolase arginase, what 2 things are produced?
urea & ornithine
what 3 enzymes are clustered together in a complex
argininosuccinate synthetase, argininosuccinase & arginase
what 2 molecules link the urea cycle & the citric acid cycle
fumarate & aspartate
how is the urea cycle regulated?
by N-acetylglutamate & arginine
how many ATP are needed per urea molecule formed
3
ammoniotelic
secrete nitrogen as ammonium
ureotelic
secrete urea
how do birds/reptiles ecrete excess nitrogen
uric acid
hyperammonemia
too much ammonium
what 2 amino acids can form ammonium
serine & theronine
acquired vs congential hyperammonemia
acquired- liver damage - hepatitis or alcohol
congential- mutation defects
glucogenic amino acid & example
catabolized to pyruvate or intermediate of CAC
alanine
ketogenic amino acid & example
catabolized to acetyl CA or acetoacetate
what 5 amino acids are ketogenic & glucogenic
tryptophan, tyrosine, threonine, phenylalanine, and isoleucine
phenylketonuria- what is it, symptoms
deficiency in phenylalanine hydroxylase, CNS symptoms
maple syrup urine disease- what is it & symptoms
deficiency in dehydrogenase complex, CNS symptoms
most genetic diseases affecting amino acid catabolism have ( ) effects
CNS
T or F: genetic diseases affecting amino acid catabolism are very rare
T
porphyrins
cyclic compounds that bind Fe 2+ or Fe 3+
all carbon & nitrogen atoms in porphyrins are contributed by ( ) & ( )
glycine & succinyl CoA
1st step in porphyrins pathway
fusion of succinyl CoA & glycine to form ALA
porphyrias
rare genetic diseases due to defects in porphyrin synthesis & accumulation of intermediates
acute intermittent porphyria
defect in PBP deaminase
how do porphyrin diseases different?
accumulation of different intermediates
what is most common porphyria?
acute
PCT vs AIT porphyria
AIT- neuro
PCT- skin lesions
3 major catecholamines
dopamine, norepinephrine & epinephrine
T or F: epinephrine is a hormone & dopamine & norepinephrine are neurotransmitters
T
what are dopamine, norepinephrine & epinephrine synthesized from?
tyrosine
histamine- how formed & what it does
decarboxylation reaction, vasodilator, allergies, inflammation & regulates gastric acid secretion
serotonin synthesis
from tryptophan via decarboxylation
creatine synthesis
glycine, arginine & methionine
what occurs with MSG
excess glutamate goes to the brain
our bodies naturally contain ( ) g of free glutamate
10
how much free glutamate in brain vs muscle
brain- 2.3g
muscle-6g
what 2 molecules transport nitrogen from muscle to liver
alanine & glutamine
2 alanine precursors
glutamate & pyruvate
2 aspartate precursors
glutamate & oxalocacetate
2 glutamate precursors
alanine & a-ketoglutarate
