Biochemistry : Biochemical Signaling
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Example Questions
Example Question #42 : Hormones And Neurotransmitters
Which neurotransmitter is synthesized in a storage vesicle?
Norepinephrine
Epinephrine
Dopamine
Dopa
Norepinephrine
Of the options given, only norepinephrine is synthesized in storage vesicles. The rest are synthesized in cytoplasm.
Example Question #101 : Biochemical Signaling
If a cell contains tyrosine hydroxylase and L-aromatic amino acid decarboxylase, it is capable of releasing what catecholamine?
Serotonin
Norepinephrine
Dopamine
Epipinephrine
Dopamine
Tyrosine hydroxylase is the rate-limiting enzyme for all catecholamine synthesis reactions. L-aromatic amino acid decarboxylase is needed to catalyze the step from DOPA to dopamine. Norepinephrine synthesis requires dopamine beta-hydroxylase and epinephrine synthesis requires dopamine beta-hydroxylase and phenylethanolamine N-methyltransferase (PNMT) in addition to the other enzymes mentioned.
Example Question #102 : Biochemical Signaling
Parkinson disease therapy is difficult because of all the following reasons except:
Dopamine does not cross blood brain barrier
L-DOPA is converted to dopamine in the brain
L-DOPA is subject to degradation
L-DOPA can be degraded by two difference enzymes
L-DOPA is converted to dopamine in the brain
Parkinson disease is associated with decreased dopamine concentration. It is commonly treated with L-DOPA, which can cross the blood brain barrier and be converted to dopamine.
Example Question #45 : Hormones And Neurotransmitters
What serves as the original substrate for serotonin synthesis?
Tyrosine
Epinephrine
Tryptophan
Dopamine
Tryptophan
Tryptophan is the original substrate for serotonin synthesis. All other answers are involved in the catecholamine synthesis pathway.
Example Question #101 : Biochemical Signaling
What is the rate-limiting enzyme for serotonin synthesis?
Tryptophan hydroxylase
Monoamine oxidase
Amino acid decarboxylase
Tyrosine hydroxylase
Tryptophan hydroxylase
Tryptophan hydroxylase is the rate-limiting step of serotonin synthesis, not to be confused with tyrosine hydroxylase.
Example Question #103 : Biochemical Signaling
What is the pharmacological use of MAO inhibitors?
Increased bioavailability of catecholamines and serotonin
Increased availability of catecholamines but not serotonin
Increased availability of serotonin but not catecholamines
Decreased bioavailability of catecholamines and serotonin
Increased bioavailability of catecholamines and serotonin
Monoamine oxidase (MAO) is responsible for inactivating catecholamines and serotonin. Thus, inhibiting MAO would result in an increase of catecholamines and serotonin.
Example Question #15 : Synapse Biochemistry
Which of the following is used to degrade catecholamines and serotonin?
Dopamine beta-hydroxylase
L-aromatic amino acid decarboxylase
Catechol-O-methyltransferase (COMT)
Phenylethanolamine N-methyltransferase (PNMT)
Catechol-O-methyltransferase (COMT)
Of the options, only COMT is involved with catecholamine and serotonin breakdown. The rest are enzymes in the catecholamine synthesis pathway.
Example Question #16 : Synapse Biochemistry
Which neurotransmitter makes up the majority of neurotransmitters released by chromaffin cells in response to stress?
Epinephrine
Dopamine
Norepinephrine
Glutamate
Epinephrine
Chromaffin cells release both epinephrine and norepinephrine, but 80% of the neurotransmitters released is epinephrine.
Example Question #21 : Synapse Biochemistry
What is the rate-limiting enzyme in catecholamine synthesis?
Dopamine beta-hydroxylase
Tryptophan hydroxylase
Tyrosine hydroxylase
Amino acid decarboxylase
Tyrosine hydroxylase
Tyrosine hydroxylase is the rate-limiting enzyme for catecholamine synthesis. It catalyzes the conversion of tyrosine to dihydroxy-phenylalanine (DOPA). Tryptophan hydroxylase is the rate-limiting step for serotonin synthesis. Dopamine beta-hydroxylase converts dopamine to norepinephrine. Amino acid decarboxylase converted DOPA to dopamine.
Example Question #22 : Synapse Biochemistry
All of the following are released from storage vesicles upon nerve firing except __________.
Epinephrine
Norepinephrine
Dihydroxyphenylalanine (DOPA)
Dopamine
Dihydroxyphenylalanine (DOPA)
Dihydroxyphenylalanine (DOPA) is the precursor for dopamine. Of the options, only dopamine, epinephrine, and norepinephrine are released upon nerve firing.
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