Synthesis of dopamine MCQs With Answer

Synthesis of dopamine MCQs With Answer

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Synthesis of dopamine MCQs With Answer is a focused study resource tailored for B. Pharm students preparing for pharmacology and medicinal chemistry exams. This introduction reviews dopamine biosynthesis, key enzymes such as tyrosine hydroxylase and aromatic L‑amino acid decarboxylase, essential cofactors like tetrahydrobiopterin and vitamin B6, regulatory mechanisms, intracellular trafficking, and clinical links to Parkinson’s disease and drug therapy (carbidopa, entacapone). The content emphasizes biochemical steps, enzyme regulation, metabolic fate, and pharmaceutical implications to build conceptual and application skills. SEO keywords included: Synthesis of dopamine MCQs With Answer, dopamine biosynthesis, tyrosine hydroxylase, L‑DOPA, B. Pharm study guide. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which enzyme catalyzes the conversion of L‑tyrosine to L‑DOPA in dopamine biosynthesis?

  • Tyrosine hydroxylase
  • Aromatic L‑amino acid decarboxylase
  • Monoamine oxidase
  • Catechol‑O‑methyltransferase

Correct Answer: Tyrosine hydroxylase

Q2. What is the immediate precursor of dopamine in the biosynthetic pathway?

  • Tyrosine
  • L‑DOPA (levodopa)
  • Norepinephrine
  • Homovanillic acid

Correct Answer: L‑DOPA (levodopa)

Q3. Which cofactor is essential for the tyrosine hydroxylase reaction?

  • Tetrahydrobiopterin (BH4)
  • Pyridoxal phosphate (PLP)
  • FAD

Correct Answer: Tetrahydrobiopterin (BH4)

Q4. Which enzyme converts L‑DOPA to dopamine?

  • Aromatic L‑amino acid decarboxylase (AADC)
  • Tyrosine hydroxylase
  • Monoamine oxidase A
  • Catechol‑O‑methyltransferase (COMT)

Correct Answer: Aromatic L‑amino acid decarboxylase (AADC)

Q5. Which vitamin serves as a coenzyme for aromatic L‑amino acid decarboxylase?

  • Pyridoxal phosphate (vitamin B6)
  • Biotin
  • Niacin
  • Vitamin K

Correct Answer: Pyridoxal phosphate (vitamin B6)

Q6. Which metal ion is required at the active site of tyrosine hydroxylase?

  • Iron (Fe2+)
  • Magnesium (Mg2+)
  • Calcium (Ca2+)
  • Zinc (Zn2+)

Correct Answer: Iron (Fe2+)

Q7. Where in the neuron does dopamine synthesis primarily occur?

  • Presynaptic cytosol of dopaminergic neurons
  • Post‑synaptic density
  • Mitochondrial matrix
  • Endoplasmic reticulum lumen

Correct Answer: Presynaptic cytosol of dopaminergic neurons

Q8. Which enzyme regenerates tetrahydrobiopterin (BH4) after it is oxidized?

  • Dihydropteridine reductase (DHPR)
  • Methylene tetrahydrofolate reductase
  • Glutathione reductase
  • Monoamine oxidase

Correct Answer: Dihydropteridine reductase (DHPR)

Q9. What is the chemical name of dopamine?

  • 3,4‑Dihydroxyphenethylamine
  • 4‑Hydroxyphenylalanine
  • 2‑Amino‑3‑hydroxybenzoic acid
  • 3,4‑Dihydroxyphenylalanine

Correct Answer: 3,4‑Dihydroxyphenethylamine

Q10. Which step is considered the rate‑limiting step in catecholamine biosynthesis?

  • Conversion of tyrosine to L‑DOPA by tyrosine hydroxylase
  • Decarboxylation of L‑DOPA to dopamine
  • Methylation by COMT
  • Oxidative deamination by MAO

Correct Answer: Conversion of tyrosine to L‑DOPA by tyrosine hydroxylase

Q11. How is tyrosine hydroxylase activity commonly regulated?

  • Phosphorylation by protein kinases increases activity
  • Proteolytic cleavage permanently activates it
  • Acetylation inhibits activity
  • Ubiquitination enhances catalytic turnover

Correct Answer: Phosphorylation by protein kinases increases activity

Q12. Which transporter loads dopamine into synaptic vesicles?

  • Vesicular monoamine transporter (VMAT2)
  • DAT (dopamine transporter)
  • Na+/K+ ATPase
  • Glutamate transporter

Correct Answer: Vesicular monoamine transporter (VMAT2)

Q13. What drives VMAT2‑mediated uptake of dopamine into vesicles?

  • Proton electrochemical gradient generated by vesicular H+‑ATPase
  • Direct ATP binding to VMAT2
  • Sodium gradient across plasma membrane
  • Calcium influx during depolarization

Correct Answer: Proton electrochemical gradient generated by vesicular H+‑ATPase

Q14. Which enzyme primarily degrades cytosolic dopamine to DOPAC?

  • Monoamine oxidase (MAO)
  • Catechol‑O‑methyltransferase (COMT)
  • Aromatic L‑amino acid decarboxylase
  • Tyrosine hydroxylase

Correct Answer: Monoamine oxidase (MAO)

Q15. Which metabolite is formed by methylation of dopamine or DOPAC and is used clinically as a urine biomarker?

  • Homovanillic acid (HVA)
  • Serotonin
  • Noradrenaline
  • Vanillylmandelic acid (VMA)

Correct Answer: Homovanillic acid (HVA)

Q16. What is the main role of carbidopa when administered with L‑DOPA?

  • Inhibits peripheral aromatic L‑amino acid decarboxylase to increase central L‑DOPA availability
  • Inhibits tyrosine hydroxylase in brain
  • Activates VMAT2 to enhance storage
  • Blocks COMT in the brain

Correct Answer: Inhibits peripheral aromatic L‑amino acid decarboxylase to increase central L‑DOPA availability

Q17. Which drug class inhibits catechol‑O‑methyltransferase (COMT) and prolongs L‑DOPA action?

  • COMT inhibitors (e.g., entacapone, tolcapone)
  • MAO‑B inhibitors
  • AADC inhibitors
  • Calcium channel blockers

Correct Answer: COMT inhibitors (e.g., entacapone, tolcapone)

Q18. Which isoform of monoamine oxidase preferentially metabolizes dopamine in the brain?

  • MAO‑B
  • MAO‑A
  • Both equally
  • Neither; COMT is primary

Correct Answer: MAO‑B

Q19. In Parkinson’s disease therapy, why is L‑DOPA preferred over dopamine for systemic administration?

  • Dopamine cannot cross the blood‑brain barrier, but L‑DOPA can
  • Dopamine is more stable in plasma than L‑DOPA
  • Dopamine has higher oral bioavailability
  • L‑DOPA is not a precursor of dopamine

Correct Answer: Dopamine cannot cross the blood‑brain barrier, but L‑DOPA can

Q20. Which enzyme methylates free catechols using S‑adenosylmethionine as methyl donor?

  • Catechol‑O‑methyltransferase (COMT)
  • Tyrosine hydroxylase
  • Aromatic L‑amino acid decarboxylase
  • Dopamine β‑hydroxylase

Correct Answer: Catechol‑O‑methyltransferase (COMT)

Q21. Which cellular compartment contains the enzyme dopamine β‑hydroxylase, converting dopamine to norepinephrine?

  • Secretory vesicles of noradrenergic neurons
  • Cytosol of dopaminergic neurons
  • Mitochondria
  • Golgi apparatus

Correct Answer: Secretory vesicles of noradrenergic neurons

Q22. Which post‑translational modification increases tyrosine hydroxylase catalytic activity during neuronal stimulation?

  • Phosphorylation at serine residues
  • Glycosylation
  • Lipidation
  • Proteolytic cleavage

Correct Answer: Phosphorylation at serine residues

Q23. Which genetic mutation or deficiency directly impairs BH4 synthesis and can reduce dopamine production?

  • GTP cyclohydrolase I deficiency
  • Tyrosine hydroxylase overexpression
  • Monoamine oxidase duplication
  • COMT hyperactivity

Correct Answer: GTP cyclohydrolase I deficiency

Q24. Which analytical technique is commonly used to quantify dopamine and its metabolites in biological samples?

  • High‑performance liquid chromatography (HPLC) with electrochemical detection
  • ELISA for DNA
  • Western blotting
  • Mass spectrometry without chromatography

Correct Answer: High‑performance liquid chromatography (HPLC) with electrochemical detection

Q25. Which statement about peripheral metabolism of L‑DOPA is true?

  • Peripheral AADC converts L‑DOPA to dopamine unless inhibited by carbidopa
  • L‑DOPA is resistant to peripheral decarboxylation
  • Peripheral COMT converts L‑DOPA to serotonin
  • L‑DOPA is metabolized only after crossing the BBB

Correct Answer: Peripheral AADC converts L‑DOPA to dopamine unless inhibited by carbidopa

Q26. Which structural feature characterizes dopamine compared to L‑DOPA?

  • Dopamine lacks the carboxylate group present in L‑DOPA
  • Dopamine has an additional carboxylate group
  • Dopamine contains a sulfhydryl group
  • Dopamine is an N‑acetylated compound

Correct Answer: Dopamine lacks the carboxylate group present in L‑DOPA

Q27. During synthetic organic preparation of dopamine derivatives, why are protecting groups for catechol hydroxyls often used?

  • To prevent oxidation and unwanted side reactions during synthesis
  • To increase basicity of the amine
  • To permanently block neurotransmitter activity
  • To enhance partitioning into lipid bilayers

Correct Answer: To prevent oxidation and unwanted side reactions during synthesis

Q28. Which pharmacological agent is a peripheral aromatic L‑amino acid decarboxylase inhibitor used with L‑DOPA?

  • Carbidopa
  • Selegiline
  • Reserpine
  • Amantadine

Correct Answer: Carbidopa

Q29. Which chemical reaction converts an amino acid (L‑DOPA) to its corresponding amine (dopamine) in synthetic organic chemistry?

  • Decarboxylation
  • Hydroxylation
  • Methylation
  • Oxidation

Correct Answer: Decarboxylation

Q30. In the context of L‑DOPA therapy, which adverse effect is directly linked to peripheral dopamine formation?

  • Nausea and vomiting due to peripheral dopamine acting on chemoreceptor trigger zone
  • Excessive salivation due to central effects only
  • Hypertension exclusively
  • Renal failure due to dopamine accumulation

Correct Answer: Nausea and vomiting due to peripheral dopamine acting on chemoreceptor trigger zone

Q31. Which enzyme is inhibited by selegiline, thereby increasing synaptic dopamine levels?

  • Monoamine oxidase B (MAO‑B)
  • MAO‑A
  • COMT
  • AADC

Correct Answer: Monoamine oxidase B (MAO‑B)

Q32. Which amino acid is the primary dietary precursor for dopamine biosynthesis?

  • L‑Tyrosine
  • L‑Tryptophan
  • L‑Phenylalanine is not related
  • L‑Methionine

Correct Answer: L‑Tyrosine

Q33. Which transporter is responsible for reuptake of dopamine from the synaptic cleft back into presynaptic terminals?

  • Dopamine transporter (DAT)
  • VMAT2
  • Serotonin transporter (SERT)
  • NMDA receptor

Correct Answer: Dopamine transporter (DAT)

Q34. Which process protects cytosolic dopamine from oxidative damage inside neurons?

  • Rapid sequestration into synaptic vesicles by VMAT2
  • Continuous methylation by COMT in cytosol
  • Export through DAT
  • Conversion into norepinephrine in dopaminergic neurons

Correct Answer: Rapid sequestration into synaptic vesicles by VMAT2

Q35. What is the primary biochemical consequence of BH4 deficiency on neurotransmitter synthesis?

  • Reduced activity of tyrosine hydroxylase leading to decreased dopamine
  • Excess dopamine due to overactive TH
  • Increased COMT activity producing more HVA
  • Enhanced VMAT2 activity

Correct Answer: Reduced activity of tyrosine hydroxylase leading to decreased dopamine

Q36. Which statement best describes peripheral COMT activity on L‑DOPA?

  • COMT methylates L‑DOPA to 3‑O‑methyldopa, reducing L‑DOPA available for brain uptake
  • COMT decarboxylates L‑DOPA to dopamine
  • COMT converts dopamine to DOPAC directly
  • COMT regenerates BH4

Correct Answer: COMT methylates L‑DOPA to 3‑O‑methyldopa, reducing L‑DOPA available for brain uptake

Q37. Which clinical laboratory measurement reflects central dopamine turnover in patients?

  • Cerebrospinal fluid homovanillic acid (CSF HVA) levels
  • Serum glucose
  • Urine serotonin levels only
  • Plasma albumin

Correct Answer: Cerebrospinal fluid homovanillic acid (CSF HVA) levels

Q38. In medicinal chemistry synthesis of dopamine analogues, which substituent change at the aromatic ring typically alters receptor selectivity?

  • Different positions or patterns of hydroxyl or methoxy substitutions on the catechol ring
  • Replacing the ethylamine chain with a methyl group only
  • Adding a phosphate group to the amine
  • Removing the aromatic ring entirely

Correct Answer: Different positions or patterns of hydroxyl or methoxy substitutions on the catechol ring

Q39. Which protein’s dysfunction leads to impaired vesicular storage and contributes to dopamine depletion in neurodegeneration?

  • VMAT2 dysfunction
  • Tyrosine hydroxylase overactivity
  • Excessive COMT expression
  • Overactive DAT necessarily protects neurons

Correct Answer: VMAT2 dysfunction

Q40. Which factor accelerates oxidative degradation of free dopamine in solution during laboratory synthesis or handling?

  • Exposure to air and alkaline pH leading to oxidation to quinones
  • Acidic pH preventing oxidation
  • Low temperature enhancing oxidation
  • Presence of antioxidants like ascorbic acid

Correct Answer: Exposure to air and alkaline pH leading to oxidation to quinones

Q41. Which pharmacological agent depletes vesicular monoamines by inhibiting VMAT and was historically used as an antihypertensive?

  • Reserpine
  • Levodopa
  • Carbidopa
  • Entacapone

Correct Answer: Reserpine

Q42. During biosynthesis, which enzyme’s activity increases in response to increased neuronal firing to replenish dopamine stores?

  • Tyrosine hydroxylase
  • COMT
  • MAO
  • Alcohol dehydrogenase

Correct Answer: Tyrosine hydroxylase

Q43. Which metabolic intermediate indicates oxidative deamination of dopamine by MAO?

  • 3,4‑Dihydroxyphenylacetic acid (DOPAC)
  • 3‑Methoxytyramine
  • Serotonin
  • 3,4‑Dihydroxybenzaldehyde

Correct Answer: 3,4‑Dihydroxyphenylacetic acid (DOPAC)

Q44. Which formulation strategy is used to improve oral bioavailability of L‑DOPA and reduce peripheral side effects?

  • Co‑administration with a peripheral AADC inhibitor like carbidopa
  • Formulation with COMT to degrade L‑DOPA
  • Simultaneous MAO‑B administration
  • Encapsulation with iron salts

Correct Answer: Co‑administration with a peripheral AADC inhibitor like carbidopa

Q45. Which of the following is NOT a common biotransformation pathway for dopamine?

  • Glycosylation
  • Methylation by COMT
  • Oxidative deamination by MAO
  • Conversion to HVA via sequential reactions

Correct Answer: Glycosylation

Q46. Which scientific principle explains why L‑DOPA crosses the blood‑brain barrier while dopamine does not?

  • L‑DOPA is transported by neutral amino acid transporters across the BBB
  • L‑DOPA is highly lipophilic and diffuses freely
  • Dopamine is actively pumped into brain by P‑glycoprotein
  • Dopamine binds albumin preventing BBB crossing

Correct Answer: L‑DOPA is transported by neutral amino acid transporters across the BBB

Q47. In laboratory chemical synthesis of dopamine, which protecting group is commonly used for catechol hydroxyls before amination steps?

  • Acetyl or methoxy methyl (MOM) protecting groups
  • Phosphate protecting groups
  • Complete removal of the aromatic ring
  • Permanent sulfonation

Correct Answer: Acetyl or methoxy methyl (MOM) protecting groups

Q48. Which adverse motor phenomenon is associated with chronic L‑DOPA therapy due to fluctuating dopamine levels?

  • On–off motor fluctuations and dyskinesias
  • Chronic hypotension only
  • Persistent hyperthermia
  • Permanent amnesia

Correct Answer: On–off motor fluctuations and dyskinesias

Q49. Which experimental approach can increase central dopamine levels without administering L‑DOPA?

  • Inhibiting MAO‑B to slow dopamine breakdown
  • Blocking VMAT2 to deplete vesicles
  • Enhancing peripheral AADC
  • Increasing COMT activity

Correct Answer: Inhibiting MAO‑B to slow dopamine breakdown

Q50. Which pharmacokinetic consideration is important when designing dopamine prodrugs to reach the brain?

  • Lipophilicity and use of transporter‑mediated uptake (e.g., amino acid transporters) to cross the BBB
  • Maximizing ionization at physiological pH to prevent BBB crossing
  • Making molecules extremely bulky to avoid metabolism
  • Ensuring complete peripheral decarboxylation before absorption

Correct Answer: Lipophilicity and use of transporter‑mediated uptake (e.g., amino acid transporters) to cross the BBB

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