Biochemistry : Synapse Biochemistry
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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.
Example Question #22 : Synapse Biochemistry
Norepinephrine can be removed from the synaptic cleft via __________.
vanillylmandelic acid (VMA)
amino acid decarboxylase
norepinephrine transporter proteins (NETs)
tryptophan hydroxylase
norepinephrine transporter proteins (NETs)
NETs are used to remove norepinephrine from the synaptic cleft. Tryptophan hydroxylase and amino acid decarboxylase are part of the serotonin synthesis pathway. VMA is a breakdown product of norepinephrine.
Example Question #23 : Synapse Biochemistry
Which of the following is true of epinephrine?
It binds to the beta-adrenergic receptors of the beta cells
It is elevated when insulin is elevated
It increases intracellular cAMP
It is released from the adrenal cortex
It increases intracellular cAMP
Epinephrine binds to the alpha-adrenergic receptors of the beta cells. Via intracellular signaling cascades beginning with the G protein-coupled receptor, adenylyl cyclase is activated, converting ATP to cAMP. Epinephrine is released from the adrenal medulla, not the adrenal cortex. It is also elevated when insulin is low, not high.
Example Question #24 : Synapse Biochemistry
The receptor present in the retina contains rhodopsin, which is excited by __________.
chemical stimulation
mechanical stimulation
ATP
photons
cAMP
photons
The receptors at work in the retina are photoreceptors, which means that they are stimulated by incoming photons. Unlike many other biochemical signaling cascades that take place in the body, stimulation of these receptors actually cause cell hyperpolarization rather than depolarization. The signal is then transmitted to the brain where the information is translated into all the associated neurological effectors that carry out vision.
Example Question #21 : Synapse Biochemistry
The neurotransmitter norepinephrine is synthesized from tyrosine by a series of reactions. In this pathway, what is the direct precursor of norephinephrine and what is the name of the enzyme that converts it to norepinephrine?
The direct precursor is phenylalanine and the enzyme is tyrosine hydroxylase.
The direct precursor is dihydroxyphenalanine and the enzyme is dopamine beta hydroxylase.
The direct precursor is dihydroxyphenalanine (DOPA) and the enzyme is dopa decarboxylase.
The direct precursor is epinephrine and the enzyme is tyrosine hydroxylase.
The precursor is dopamine, the enzyme is dopamine beta hydroxylase.
The precursor is dopamine, the enzyme is dopamine beta hydroxylase.
The neurotransmitter norepinephrine is synthesized from tyrosine by a series of reactions. In this pathway, tyrosine is converted to dihydroxyphenalanine (DOPA) by tyrosine hydroxylase. DOPA is converted to dopamine by DOPA decarboxylase. Dopamine is the direct precursor of norepinephrineand is converted to it by dopamine beta hydroxylase. Epinephrine is converted from norepinephrine by phenylethanolamine N-methyltransferase.
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