Amino Acids as Metabolic Precursors

Question 1

phenylalanine hydroxylase

Answer 1

converts phenylalanine is converted to tyrosine via coenzyme tetrahydrobiopterin

Question 2

phenylketone formation

Answer 2

when phenylalanine hydroxylase is not active, phenylalanine gets converted to phenylketones such as phenylpyruvate

Question 3

phenyl ketonuria

Answer 3

PKU- phenylalanine hydroxylase is deficient, causing blood levels of phenylalanine and phenylketone to rise

results in developmental defects, hyperactivity, mental retardation, deficient pigmentation

Question 4

PKU treatment

Answer 4

low phenylalanine diet (no aspartame) and tyrosine to make up for the allosteric inactivation of tyrosine hydroxylase via high levels of phenylalanine

Question 5

tetrahydrobiopterin

Answer 5

the fully reduced form of the coenzyme biopterin, this is the active form. important in rxns for synthesis of tyrosine, dopamine, and serotonin b/c it is required for tyrosine. tryptophan, and phenylalanine hydroxylases

created in rxns using GTP, GTP cyclohydrolase and dihydrolfolate reductase

deficiencies in enzymes that synthesize or reduce cause hyperphenylalaninemias

Question 6

describe synthesis of dopamine and norepinephrine

Answer 6

tyrosine to dopa via tyrosine hydroxylase

dopa to dopamine via DOPA-decarboxylase

dopamine to norepinephrine via dopamine B-hydroxylase

Question 7

DOPA

Answer 7

precursor in synthesis of dopamine but also melanin. hyperphenylalaninemias cause pigmentation defects b/c of reduced melanin

Question 8

describe serotonin synthesis

Answer 8

synthesized from tryptophan

tryptophan to 5HT via tryptophan hydroxylase

5HT to serotonin via 5HT cecarboxylase

Question 9

histamine synthesis

Answer 9

decarboxylation of histidine

vb6 dependent

mediates inflammatory rxns and gastric acid secretion

Question 10

GABA synthesis

Answer 10

decarboxylation of glutamate- major inhibitory neurotransmitter

Question 11

NO synthesis and actions

Answer 11

arginine is converted via nitric oxide synthase

acts in neurotransmission, muscle relaxation, and immune system

Question 12

how does NO cause muscle relaxation?

Answer 12

activates guanylyl cyclase

Question 13

how does nitroglycerin control angina

Answer 13

it decomposes to NO, which relaxes heart muscles

Question 14

describe how tetrahydrobiopterin is regenerated after its use in making tyrosine, DOPA, or 5HT?

Answer 14

2 ways

the oxidized product is quinonoid dihydrobiopterin. This can be reduced using NADPH and dihydropteridine reductase back to tetrahydrobiopterin

alternatively, it can be created de novo using GTP, GTP cyclohydrolase, and dihydrobiopterin synthase