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Questions and Answers
Which statement accurately describes the nature of phenylalanine and tyrosine?
Which statement accurately describes the nature of phenylalanine and tyrosine?
What is one of the anabolic fates of tyrosine?
What is one of the anabolic fates of tyrosine?
Which condition is a metabolic disorder associated with phenylalanine?
Which condition is a metabolic disorder associated with phenylalanine?
What is a clinical manifestation of phenylketonuria?
What is a clinical manifestation of phenylketonuria?
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How is tyrosine synthesized in the body?
How is tyrosine synthesized in the body?
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What role does melanin play in the body?
What role does melanin play in the body?
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What is a consequence of mental retardation in phenylketonuria?
What is a consequence of mental retardation in phenylketonuria?
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What is required for the diagnosis of phenylketonuria in newborns?
What is required for the diagnosis of phenylketonuria in newborns?
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Study Notes
Amino Acid Metabolism
- Phenylalanine and tyrosine are aromatic amino acids
- Both are mixed glucogenic and ketogenic
- Phenylalanine is essential, while tyrosine is non-essential
- Tyrosine is synthesized from phenylalanine in the liver
Tyrosine Synthesis
- The process involves phenylalanine hydroxylase, oxygen, water, tetrahydrobiopterin, and dihydrobiopterin reductase
- The reaction converts phenylalanine to tyrosine
Anabolic Fates of Tyrosine
- Tyrosine is used to synthesize proteins and phosphoproteins
- It is used to synthesize catecholamines.
Catecholamines Synthesis
- Catecholamines include adrenaline (epinephrine) and noradrenaline (norepinephrine)
- Adrenaline is primarily synthesized in the adrenal medulla
- Noradrenaline is synthesized in the adrenal medulla and adrenergic nerve endings
Melanin Synthesis
- Melanin protects skin from UV rays, acting as a natural antioxidant
- Stored in melanocytes
- Synthesized from tyrosine via tyrosinase (tyrosine hydroxylase)
Thyroid Hormone Biosynthesis
- Iodine is transported and concentrated by thyroid follicles
- Iodide is oxidized to iodine
- Tyrosine residues on thyroglobulin are iodinated (MIT and DIT)
- MIT and DIT combine to form T3 and T4
Metabolic Disorders of Phenylalanine
- Phenylketonuria (PKU) - caused by a deficiency of phenylalanine hydroxylase or dihydrobiopterine reductase
- Leads to phenylalanine accumulation in the blood and urine
- An alternative pathway creates phenylpyruvate, phenylacetate, and phenyllactate, leading to a characteristic "mossy" odor in urine
Clinical Manifestations of PKU
- Mental retardation due to impaired pyruvate transport in the brain
- Failure to thrive and seizures
- Skin lesions (eczema), light colored hair and skin (due to competitive inhibition of tyrosinase)
Diagnosis of PKU
- Screening test using ferric chloride (FeCl3) performed within 4 days of birth
- Amino acid profile (aminogram) can be used
Albinism
- Inherited genetic deficiency of tyrosinase (tyrosine hydroxylase)
- Leads to absence of melanin pigment
- Types include ocular, cutaneous, and oculocutaneous albinism
Alkaptonuria
- Inherited autosomal recessive deficiency of homogentisic acid oxidase
- Leads to arthritis and generalized pigmentation (ochronosis)
- Urine turns brownish-black upon exposure to air due to oxidation of homogentisic acid
- Diagnosed by Fehling's test
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Description
Explore the fascinating processes of amino acid metabolism, focusing on phenylalanine and tyrosine. This quiz covers their synthesis, metabolic fates, and the production of important compounds like catecholamines and melanin. Test your knowledge of these essential biochemical pathways.
