🔬
Foundation Sciences · Biochemistry

Phenylalanine and Tyrosine Metabolism

⏱️ 45–60 minutes read 📖 Biochemistry

Conversion of phenylalanine to tyrosine by phenylalanine hydroxylase (BH4 cofactor), and tyrosine to catecholamines, melanin, thyroid hormone and fumarate.

📌 Learning Objectives

  • Describe the key principles of phenylalanine and tyrosine metabolism.
  • Explain the clinical relevance of phenylalanine and tyrosine metabolism.
  • Recognise common conditions linked to phenylalanine and tyrosine metabolism in MLA-style scenarios.

📋 Overview

Conversion of phenylalanine to tyrosine by phenylalanine hydroxylase (BH4 cofactor), and tyrosine to catecholamines, melanin, thyroid hormone and fumarate. This topic integrates with pathology, pharmacology and clinical medicine and is frequently tested in UK medical school exams and the MLA.

🔬 Basic Science

Conversion of phenylalanine to tyrosine by phenylalanine hydroxylase (BH4 cofactor), and tyrosine to catecholamines, melanin, thyroid hormone and fumarate. Detailed mechanisms, regulation and molecular interactions underpin both normal physiology and disease.

🏥 Clinical Relevance

Newborn heel-prick for PKU; low-Phe diet; aspartame caution.

🧪 Investigations

Relevant laboratory tests, imaging or histological examination are used as appropriate to the clinical context.

💊 Management

Management is condition-specific; principles include addressing the underlying biochemical/structural derangement, supportive care and targeted therapy where available.

Revision Resources – expand the sections below for high-yield notes, exam pearls, key facts and further reading.

🎯 MLA High-Yield Notes & Quick Revision ⌄
High-yield topic for the UK MLA — frequently appears in SBA questions linking biochemistry concepts to clinical presentations and management decisions.
Applying biomedical science to clinical practice Diagnosis and investigation Pathophysiology of common conditions
  • Conversion of phenylalanine to tyrosine by phenylalanine hydroxylase (BH4 cofactor), and tyrosine to catecholamines, melanin, thyroid hormone and fumarate.
⭐ Exam Pearls ⌄
⭐ High Yield
PAH deficiency → phenylketonuria (PKU)
BH4 cofactor deficiency: malignant PKU
Tyrosinase deficiency → albinism
Alkaptonuria: homogentisate oxidase deficiency, dark urine
💡 Clinical Pearl
: Newborn heel-prick for PKU; low-Phe diet; aspartame caution.
⚠️ Exam Tip — Common Mistakes
Confusing phenylalanine and tyrosine metabolism with related but distinct mechanisms.
Memorising pathways without linking to clinical disease.
🔑 Key Facts ⌄
PAH deficiency → phenylketonuria (PKU)
BH4 cofactor deficiency: malignant PKU
Tyrosinase deficiency → albinism
Alkaptonuria: homogentisate oxidase deficiency, dark urine
📚 References ⌄
  1. BMJ Best Practice
  2. Robbins Basic Pathology
  3. Lippincott Illustrated Reviews: Biochemistry
  4. Wheater's Functional Histology
  5. NICE guidance where applicable.

Further Resources

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