Amino Acid Metabolism

Question 1

Only ______ form of amino acids are found in proteins

Answer 1

L-form

Question 2

Leu and Lys are ketogenic/glucogenic?

Answer 2

ketogenic - give in PDH deficiency to prevent the build-up of more pyruvate

Question 3

Rate-limiting step in urea cycle

Answer 3

Carbamoyl Phosphate Synthetase I

+ NAG (product of AA)

Requires 2 ATP to form Carbamoyl phosphate, a high energy compound that is converted to citrulline before shuttling out to cytosol to continue urea cycle

Question 4

Order of steps in urea cycle

Answer 4

Ordinarly, Careless Crappers Are Also Frivolous About Urination

Ornithine (+Carbomoyl Phosphate) –> Citrulline –> Aspartate –> Arginosuccinate –> Fumarate (TCA) + Arginine –> Urea + Ornithine

Question 5

Where are the two nitrogens in urea from?

Answer 5

1) Carbamoyl phosphate

2) Aspartate

Question 6

What are the three main sources of nitrogen in the urea cycle?

Answer 6

1) Oxidative deamination of glutamate into alpha-ketoglutarate and free ammonia
2) glutamine –> glu + NH4 (glutaminase) from muscles
3) Transamination of glu + OAA –> aspartate + alpha-ketoglutarate

Question 7

Hyperammonia results in excess NH4+, which depletes ____________, leading to inhibition of TCA cycle

Answer 7

alpha-ketoglutarate

Question 8

Treatment of hyperammonia

Answer 8

1) Limit protein diet
2) Benzoate or pheylbutyrate (bind amino acid and lead to excretion)
2) Lactulose to acidify the GI tract and trap NH4+ for excretion

Question 9

Symptoms of ammonia intoxication

Answer 9

Tremor (asterixis), slurred speech, somnolence, vomiting, cerebral edema, blurring of vision

Question 10

Catecholamine synthesis: What is the name of the enzyme that converts phenylalanine to tyrosine? Cofactor?

Answer 10

Step 1 - Phenyalanine Hydrosylase

Cofactor: Dihydropteridine reductase, requires THF

Question 11

Tyrosine is used to make the hormone ___________

Answer 11

Thyroxine

Question 12

Catecholamine synthesis: What is the name of the enzyme that converts tyrosine to DOPA? Cofactor?

Answer 12

Step 2 - Tyrosine Hydoxylase

Cofactor: Dihydropteridine reductase, requires THF

Question 13

Catecholamine synthesis: What is the name of the enzyme that converts DOPA to dopamine? Cofactor?

Answer 13

Step 3 - DOPA Decarboxylase

Cofactor - B6

Question 14

DOPA can be converted into catecholamines and ____________

Answer 14

melanin

Question 15

Catecholamine synthesis: What is the name of the enzyme that converts dopamine to Norepi? Cofactor?

Answer 15

Dopamine Beta Hydroxylase, Step 4

Cofactor: Vitamin C

Question 16

Catecholamine synthesis: What is the name of the enzyme that converts Norepi to epi? Cofactor?

Answer 16

PNMT, Step 5

Cofactor: SAM

Question 17

HVA is a breakdown product of ____________

Answer 17

dopamine

Question 18

VMA is a breakdown product of ____________

Answer 18

norepinephrine

Question 19

Metanephrine is a breakdown product of ___________

Answer 19

epinephrine

Question 20

Niacin and serotonin are products of ___________

Answer 20

niacin

Question 21

Melatonin is derived from ______________

Answer 21

serotonin

Question 22

Glycine is converted to porphyrin and then to _______ with the help of B6

Answer 22

heme

Question 23

Creatinine, Urea, and NO are products of ____________

Answer 23

arginine

Question 24

GABA and Glutathione are products of _____________

Answer 24

glutamate