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Questions and Answers
What is the rate-limiting step in catecholamine biosynthesis?
What is the rate-limiting step in catecholamine biosynthesis?
- Crossing of the blood-brain barrier by catecholamines
- Ring hydroxylation of L-tyrosine to L-dopa (correct)
- Conversion of L-dopa to dopamine
- Formation of pyridoxal phosphate
Which enzyme catalyzes the conversion of L-tyrosine to L-dopa?
Which enzyme catalyzes the conversion of L-tyrosine to L-dopa?
- Phenylethanolamine N-methyltransferase
- Dopamine beta-hydroxylase
- Tyrosine hydroxylase (correct)
- Dopa decarboxylase
Which compound can cross the blood-brain barrier and is used for treatment in diseases like Parkinson's?
Which compound can cross the blood-brain barrier and is used for treatment in diseases like Parkinson's?
- L-dopa (correct)
- Tetrahydropteridine
- L-tyrosine
- Dopamine
In the presence of which cofactor does dopa decarboxylase catalyze the conversion of L-dopa to dopamine?
In the presence of which cofactor does dopa decarboxylase catalyze the conversion of L-dopa to dopamine?
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What role does a-methyldopa play in the catecholamine biosynthesis pathway?
What role does a-methyldopa play in the catecholamine biosynthesis pathway?
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What is the end product of the ring hydroxylation step in catecholamine biosynthesis?
What is the end product of the ring hydroxylation step in catecholamine biosynthesis?
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Study Notes
Catecholamine Biosynthesis
- Occurs in the cytoplasm of chromaffin cells
Ring Hydroxylation
- Converts L-tyrosine to L-dopa
- Catalyzed by tyrosine hydroxylase in the presence of tetrahydropteridine
- Irreversible reaction
- Rate-limiting step of catecholamine biosynthesis
- Catecholamines cannot cross the blood-brain barrier, must be synthesized locally
- L-dopa can cross the blood-brain barrier, used to treat CNS diseases like Parkinson's disease
Decarboxylation
- Converts L-dopa to dopamine
- Catalyzed by dopa decarboxylase in the presence of pyridoxal phosphate
- Irreversible reaction
- Compounds like a-methyldopa act as competitive inhibitors, treating hypertension caused by high catecholamine levels
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