U01.01.107 Amino acid derivatives

Amino acids serve as precursors to a wide range of biologically significant molecules. Understanding these derivatives is crucial for mastering biochemistry concepts tested on the USMLE Step 1.

Key Amino Acid Derivatives

1. Tryptophan Derivatives

Niacin → Forms NAD+/NADP+ (essential for redox reactions).
Serotonin → Converted into Melatonin (involved in circadian rhythms and mood regulation).

2. Phenylalanine and Tyrosine Derivatives

Phenylalanine → Precursor of Tyrosine (requires Phenylalanine hydroxylase and BH4).
- Tyrosine derivatives:
  - Dopa → Precursor for Dopamine, which further converts to:
    - Norepinephrine (NE)
    - Epinephrine (Epi)
  - Thyroxine (thyroid hormone critical for metabolism).

3. Histidine Derivative

Histamine → Mediator of allergic reactions, gastric acid secretion, and inflammation.

4. Glycine Derivatives

Porphyrin → Forms Heme (key component of hemoglobin and cytochromes).

5. Arginine Derivatives

Nitric Oxide (NO) → A potent vasodilator, synthesized using BH4 and NO synthase.
Urea → Formed via the urea cycle to excrete ammonia.

Summary Table of Amino Acid Derivatives

Amino Acid	Derivative	Biological Role
Tryptophan	Niacin (NAD+/NADP+)	Redox reactions
	Serotonin → Melatonin	Mood, circadian rhythm regulation
Phenylalanine	Tyrosine	Precursor for thyroid hormones, neurotransmitters
Tyrosine	Dopa → Dopamine → NE → Epi	Neurotransmitters, metabolic regulation
	Thyroxine	Thyroid hormone
Histidine	Histamine	Allergy, gastric acid, inflammation
Glycine	Porphyrin → Heme	Oxygen transport, electron transport chain
Arginine	Nitric Oxide (NO)	Vasodilation, immune modulation
	Urea	Ammonia excretion

Key Points to Remember

BH4 (Tetrahydrobiopterin) is essential for:
- Conversion of Phenylalanine to Tyrosine.
- Synthesis of Dopa and Nitric Oxide.
Impairment in pathways, such as in Phenylketonuria (PKU), can lead to severe clinical manifestations.
Amino acid derivatives often play regulatory roles in metabolism, neurotransmission, and immunity.
Memorize the pathway intermediates for tyrosine-derived catecholamines and the enzymes involved (e.g., tyrosine hydroxylase).

USMLE Step 1 Review Series

Curriculum

U01.01.107 Amino acid derivatives

Key Amino Acid Derivatives

1. Tryptophan Derivatives

2. Phenylalanine and Tyrosine Derivatives

3. Histidine Derivative

4. Glycine Derivatives

5. Arginine Derivatives

Summary Table of Amino Acid Derivatives

Key Points to Remember

Bibliography Reference Links

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