urea cycle

T/F: amino acids are stored in the body

• false

Amino acids have to be obtained from

I: the diet

II: de novo synthesis

III: protein degradation

a) I and II

b) II and III

c) II ONLY

d) I, II, and III

d) I, II, and III

catabolism of amino acids involves the removal of _____

a) hydroxyl group

b) nitrogen

c) urea

d) alpha-ketoacid

b) nitrogen

the removal of nitrogen from amino acids is released as what 3 forms?

• ammonia

• urea

• uric acid

describe protein digestion in the stomach

• HCl denatures the protein

• HCl activates pepsinogen → pepsin

  • pepsin breaks protein → polypeptides

describe protein digestion in the pancreas. what specific enzymes are used?

• protease enzymes to break down polypeptides → oligopeptides

  • trypsin

  • chymotrypsin

  • elastase

  • carboxypeptidase

describe protein digestion in the small intestine

• aminopeptidases

  • cleave oligopeptides → small peptides + free amino acids (go to the liver)

SATA: which of the following matches the right enzyme to the location?

a) pepsin; small intestine

b) trypsin; pancreas

c) carboxypeptidase; stomach

d) aminopeptidase; small intestine

b) trypsin; pancreas

d) aminopeptidase; small intestine

what is transamination in the catabolism of amino acids? what is the product?

• transfer alpha-amino group to alpha-ketoglutarate

• product = glutamate and an alpha-ketoacid

what general enzyme is used to transfer the alpha-amino group to alpha-ketoglutarate ?

a) aminotransferase

b) amidotransferase

c) dehydrogenase

d) lyase

a) aminotransferase

what prosthetic group is used to help with the transamination step ?

a) Vit B5

b) Vit B3

c) Vit B2

d) Vit B6

d) Vit B6

• pyridoxal phosphate

aspartate aminotransferase reaction (what are the substrates + products?)

• aspartate → oxaloacetic acid (alpha-ketoacid)

• alpha-ketoglutaric acid → glutamic acid

alanine aminotransferase reaction (what are the substrates + products?)

• alanine → pyruvic acid (alpha-ketoacid)

• alpha-ketoglutaric acid → glutamic acid

the ____ ______ transfers the amino group

• pyridoxal phosphate

pyruvate, oxaloacetate, and alpha-ketoglutarate are all …

a) beta-ketoacids

b) alpha-hydroxyacids

c) alpha-ketoacids

d) none of the above

c) alpha-ketoacids

• C=O (ketone) on the carbon adjacent to the -COOH group

SATA: which of the following are the correct alpha-ketoacid and amino acid pair?

a) alanine & pyruvate

b) alanine & oxaloacetic acid

c) aspartic acid & pyruvate

d) aspartic acid and oxaloacetic acid

a) alanine & pyruvate

d) aspartic acid and oxaloacetic acid

what enzyme performs oxidative deamination?

• glutamate dehydrogenase

SATA: what redox factors are used for oxidative deamination?

a) FAD

b) NAD+

c) NADP+

d) vit B6

b) NAD+

c) NADP+

what are the products of oxidative deamination?

• alpha-ketoacids

• ammonia (NH₃)

  • then converted to urea in the urea cycle (liver)

what is reduced? what is oxidized in the oxidative deamination reaction?

• NAD+ or NADP+ = reduced → NADH or NADPH

• glutamate = oxidized → alpha-ketoglutarate

what is the major disposal form of amino groups from amino acids?

a) uric acid

b) urea

c) nitrogen

d) CO2

b) urea

urea is derived from what 3 substances?

• ammonia

• aspartate

• carbon dioxide

what amino acid is used to help make urea?

a) E

b) Q

c) D

d) Q

e) A

c) D

list the steps in the urea cycle

1. CO2 + NH3 + 2ATP → (carbamoyl phosphate synthetase I) → carbamoyl phosphate

2. carbamoyl phosphate + L-ornithine → (ornithine trans-carbamoylase) → L-citrulline

3. L-citrulline leaves mitochondrion

4. L-citrulline + L-aspartate → (arginosuccinate synthetase) (+ATP) → argininosuccinate

5. argininosuccinate → (argininosuccinate lyase) → L-arginine + fumarate

6. L-arginine → (arginase) → urea + L-ornithine

7. ornithine enters mitochondrion

what substance allows a constant supply of L-ornithine in the mitochondria?

a) L-citrulline

b) argininosuccinate

c) L-aspartate

d) L-arginine

arginine

where is L-ornithine produced? where does L-ornithine react with carbamoyl phosphate?

• produced in the cytosol

• reacts in the matrix of mitochondria

where is L-citrulline produced? where does L-citrulline react with L-aspartate?

• produced in the mitochondria matrix

• reacts in the cytosol

carbamoyl phosphate synthetase I reaction

• CO2 + NH3 + 2ATP → carbamoyl phosphate

ornithine transcarbamoylase reaction

• L-ornithine + carbamoyl phosphate → L-citrulline

argininosuccinate synthetase reaction

• L-aspartate + L-citrulline → (ATP) → argininosuccinate

argininosuccinate lyase reaction

• argininosuccinate → fumarate + L-arginine

arginase reaction

• L-arginine → urea + L-ornithine

what reaction produces fumarate as a byproduct?

a) L-aspartate → argininosuccinate

b) argininosuccinate → L-arginine

c) L-arginine → L-ornithine

d) L-ornithine → L-citrulline

b) argininosuccinate → L-arginine

NH3 is converted to urea in the ____

• liver

what happens to fumarate in the urea cycle?

• gluconeogenesis

  • fumarate → malate → oxaloacetate

    • oxaloacetate + glutamate → L-aspartate

essential vs non-essential amino acids

• essential = get from diet

• non-essential = can synthesize

glucogenic amino acid catabolism yields …

• pyruvate or intermediates of the TCA cycle

  • substrates for gluconeogenesis

ketogenic amino acid catabolism yields …

• acetoacetate

  • or its precursors = acetyl CoA and/or acetoacetyl CoA

  • substrates for ketogenesis

T/F: ketogenic amino acids give rise to the net formation of glucose

• false

all nonessential amino acids are at least

a) glucogenic

b) ketogenic

c) glucogenic and ketogenic

d) none of the above

a) glucogenic

what are the 6 families of pathways that amino acid biosynthesis can provide?

• glutamate

• aspartate

• serine

• alanine

• aromatic AA

• histidine

What essential AAs are glucogenic?

• Histidine (His, H)

• Methionine (Met, M)

• Threonine (Thr, T)

• Valine (Val

What are non-essential AAs are glucogenic?

• alanine (Ala, A)

• Arginine (Arg, R)

• aspartate (Asp, D)

• Cysteine (Cys, C)

• Glutamate (Glu, E)

• Glutamine (Gln, Q)

• glycine (Gly, G)

• Proline (Pro, P)

• Serine (Ser, S

What essential AAs are both glucogenic and ketogenic?

• Isoleucine (Ile, I)

• Phenylalanine (Phe, F)

• Tryptophan (Trp, W)

What non essential AA is both glucogenic and ketogenic?

• Tyrosine (Tyr, Y)

What essential AAs are ketogenic?

• Leucine (Leu, L)

• Lysine, (Lys, K)

What is the source of the glutamate family?

alpha-KG (TCA)

What is the source of the aspartate family?

OAA (TCA)

What is the source of the serine family?

3-phosphoglycerate (gluconeogenesis/glycolysis)

What is the source of the alanine family?

pyruvate (glucogenic)

What is the source of the aromatic AA family?

• phopshoenolpyruvate

• erythrose 4-phosphate (pentose phosphate pathway/PPP)

What is the source of the histidine family?

ribose 5-phosphate (PPP)

What are the specialized products of AAs?

• porphyrins (Hb)

• creatine (muscle mass)

• NTs (5-HT, catecholamines)

• purines + pyrimidines (nucleic acids)

• other N containing compounds (melanin)