Urea Cycle Lecture Notes

Introduction to Nitrogen Disposal

• Excess Nitrogen: Needs to be removed from organisms
  • Fish & Amphibians: Diffuse ammonia/ammonium into the water
  • Humans: Convert nitrogen into urea
  • Reptiles & Birds: Excrete uric acid (insoluble in water)

Importance of Urea

• Characteristics:
  • Non-toxic
  • Water-soluble
• Purpose: Safely dispose of excess ammonium ions (which are toxic)

Overview of Urea Cycle

• Purpose: Convert toxic ammonium into non-toxic urea
• Process:
  1. Transport: Ammonium ions travel to the liver via glutamate or glutamine
  2. Formation of Carbamoyl Phosphate:
     • Ammonium + CO₂ + ATP → Carbamoyl Phosphate
     • Enzyme: Carbamoyl Phosphate Synthetase 1 (CPS 1)
     • Components:
       • Red: Ammonium ion (amino group)
       • Green: CO₂ (carbonyl group)
       • Phosphate group from ATP
  3. Urea Cycle Intermediates:
     • Apartate: Recognizable amino acid
     • Fumarate: Intermediate from TCA cycle
     • End Product: Urea

Excretion of Urea

• Pathway: Liver → Blood (water-soluble) → Kidneys → Urine
• Alternative excretion: Some urea is excreted in sweat

Extra Notes

• Tutor available in Southern California
  • Contact: MOOC University at gmail.com