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CMBM Exam 4 Gopi > Urea cycle > Flashcards

Urea cycle Flashcards

0
Q

Glutamate dehydrogenase

A

reductive amination of alpha-ketoglutarate

alpha-ketoglutarate to L-glutamate and produces NAD(P)

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1
Q

Ammonia metabolism in Hepatocytes

A

Periportal hepatocytes - High capacity, low affinity
Perivenous hepatocytes - low capacity, high affinity (glutamine synthetase detoxes NH3, incorporates NH3 into glutamine)
glutamine is a nitrogen carrier

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2
Q

Glutamine synthetase

A

glutamate + NH4 converted to Glutamine

produces ADP

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3
Q

Glutamate role in ammonia transport

A

hands off NH3 to alanine

in the liver, it hands off NH3 for incorporation into urea

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4
Q

synthesis of Nitric oxide (NO) from arginine

A

NO is a gas hormone
diffuses rapidly into cells
activates cGMP synthesis and relaxes blood vessels and lowers BP
neurotransmitter in brain - high levels during stroke kill neurons
Nitroglycerin converted to NO and dilates coronary arteries in treating angina pectoris

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5
Q

Fate of ammonia: 3 major reactions in all cells

A

Glutamate dehydrogenase - reductive amination of alpha-ketoglutarate to form glutamate
Glutamine synthetase - ATP dep. amidation of y-carboxyl of glutamate to glutamine
Carbamoyl phosphate synthetase I - two ATP required, one to activate bicarb and one to phosphorylate carbamate

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6
Q

At physiologic pH equilibrium favors NH4+ by a factor of

A

100/1

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7
Q

NH3 can cross membranes

A

passes into urine from kidney tubules cells and decreases acidity of urine by binding protons and forms NH4+ which cannot cross membranes

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8
Q

Transamination

A

is the transfer of an amino group from an alpha amino acid to alpha keto acid

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9
Q

serine can make

A

cysteine

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10
Q

Glycine and ____ are interconvertible

A

serine

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11
Q

Glucogenic Amino acids

A 
Ala, ser, cys, gly, thr, trp = pyruvate 
asp, arg = OAA 
Ile, Met, Val = succinyl CoA 
Asp, Phe, Tyr = fumarate 
Arg, Gln, Glu, Pro, His = alpha ketoglutarate
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12
Q

Ketogenic amino acids

A

Leu, Lys, Phe, Tyr = acetoacetate
Ile, Leu, Thr, Trp = acetyl CoA
Only ketogenic = Leu and Lys

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13
Q

Breakdown of branched chain amino acids

A

Leucine, valine and Isoleucine
broken down to acetoacetate and acetyl CoA
via HMG-CoA which is an intermediate in CH and KB

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14
Q

Transamination reaction

A

done via PLP = pyridoxal phosphate, cofactor B6

Aspartate and alpha-ketoglutarate to OAA and glutamate

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15
Q

Glucose-Alanine cycle

A

shuttles NH3 from muscle to liver via Alanine which is converted back to pyruvate then to glucose
pyruvate is alanine plus amino group

16
Q

Glutamine

A

synthesized in peripheral tissues from glutamate and NH3
glutamine is shuttled to liver where the NH3 is removed (glutamate) and another is removed (alpha-ketoglutarate) both NH3 and added to Urea

17
Q

What happens to protein in the FED state?

A

AA has CO2 removed

incorporated in protein or TAG or Glucose or shuttled to cells

18
Q

what happens to amino acids in the FASTING state?

A

protein is broken down into AA
goes through the TCA cycle to glutamine where in peripheral tissues converted back to alanine or allows carriage of NH3 to kidneys for excretion
or Alanine from breakdown to liver for KB and Glucose and excess NH3 to urea

19
Q

how does OAA contribute NH3 to the urea cycle?

A

reacts with glutamate to generate alpha-ketoglutarate and aspartate
Aspartate combines with citrulline to start the cycle in the cytoplasm

20
Q

what does glutamate do?

A

collects NH3 from AA through transamination to deliver it to Aspartate

21
Q

Components of urea cycle

A

NH3 and Co2 combine to make carbamoyl phosphate
this reacts with ornithine to make citrulline
Citrulline exits the mitochondria
citrulline and aspartate combine (uses ATP to AMP) to make argininosuccinate which splits into Fumarate and Arginine
Arginine back to Ornithine in the mitochondria gives off NH3 which is combined with H20 to make Urea

22
Q

NH4+ and bicarb and ATP =

A

Carbamoyl phosphate
requires 2 ATP
catalyzed by carbamoyl phosphate synthetase I
this in the liver and intestines

23
Q

Carbamoyl phosphate and ornithine =

A

citrulline

crosses out of mito and into cytosol

24
Q

citrulline and aspartate =

A

make argininosuccinate

25
Q

Argininosuccinate

A

splits to Arginine and Fumarate

26
Q

Arginine in the urea cycle

A

which is just NH4 and aspartate
splits to urea and ornithine
ornithine is exchanged with citrulline

27
Q

Regulation of Urea cycle

A

higher ammonia leads to more urea production
feed forward regulation
1. allosteric activation of CPSI by NAG
2. induction/repression of synthesis of urea cycle enzymes
NAG is made from acetyl CoA and glutamate
Arginine stimulates the cycle
prolonged fasting or protein degradation increases the cycle

28
Q

Urea cycle defects can cause

A 
feeding difficulty 
vomiting 
lethargy 
irritability 
tachypnea
convulsive crisis 
acute encephalophaty 
coma when serum over 300umol/L
29
Q

how would treat urea cycle defect?

A

L-arginine and L-carnitine
sodium benzoate and sodium phenylbutarate
Long term - low protein diet, liver transplant and dialysis

30
Q

Hyperammonia

A

150 ulmol/L neonates

80 ulmol/L adult and children

31
Q

Disorder of the urea cycle

A

ammonia can accumulate - toxic to nervous system
free NH3 rapidly fixed to a-ketoglutarate to glutamate to pyruvate which makes Alanine and is transported to the liver
see elevated glutamine as well

32
Q

what aids Nitrogen removal from the body?

A

Benzoic acid and Phenylbutyrate
Benzoic + glycine makes Hippuric acid and the body must make serine to replace lost glycine
Phenylbutyrate + glutamine = conjugate is excreted
Body uses glucose and 2 nitrogens to remake glutamine

33
Q

2 alanine =

A

1 glucose

34
Q

2 nitrogen =

A

1 Urea

35
Q

Urea cycle during fasting

A

liver maintains glucose
muscle is major carbon source
excretion of urea is high eventually less muscle protein used and urea decreases
Brain switches to KB

36
Q

Glucagon release during fasting stimulates

A

alanine transport to the liver

CMBM Exam 4 Gopi (10 decks)

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