Biochemistry : Biochemistry

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #42 : Hormones And Neurotransmitters

Which of the following neurotransmitters do chromaffin cells release?

Possible Answers:

Dopamine

Glutamate

Serotonin

Epinephrine

Correct answer:

Epinephrine

Explanation:

Chromaffin cells are located in the adrenal gland, and release epinephrine and norepinephrin.

Example Question #42 : Hormones And Neurotransmitters

Which neurotransmitter is synthesized in a storage vesicle?

Possible Answers:

Norepinephrine

Epinephrine

Dopamine

Dopa

Correct answer:

Norepinephrine

Explanation:

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?

Possible Answers:

Serotonin

Norepinephrine

Dopamine

Epipinephrine

Correct answer:

Dopamine

Explanation:

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:

Possible Answers:

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

Correct answer:

L-DOPA is converted to dopamine in the brain

Explanation:

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?

Possible Answers:

Tyrosine

Epinephrine

Tryptophan

Dopamine

Correct answer:

Tryptophan

Explanation:

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?

Possible Answers:

Tryptophan hydroxylase

Monoamine oxidase

Amino acid decarboxylase

Tyrosine hydroxylase

Correct answer:

Tryptophan hydroxylase

Explanation:

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?

Possible Answers:

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

Correct answer:

Increased bioavailability of catecholamines and serotonin

Explanation:

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?

Possible Answers:

Dopamine beta-hydroxylase

L-aromatic amino acid decarboxylase

Catechol-O-methyltransferase (COMT)

Phenylethanolamine N-methyltransferase (PNMT)

Correct answer:

Catechol-O-methyltransferase (COMT)

Explanation:

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?

Possible Answers:

Epinephrine

Dopamine

Norepinephrine

Glutamate

Correct answer:

Epinephrine

Explanation:

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?

Possible Answers:

Dopamine beta-hydroxylase

Tryptophan hydroxylase

Tyrosine hydroxylase

Amino acid decarboxylase

Correct answer:

Tyrosine hydroxylase

Explanation:

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. 

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