gen-define-atp-as-an-energy-currency-and-give-one-short-worked-e-c835

Define ATP as an energy currency and give one short worked example.

# ATP as an Energy Currency **ATP (Adenosine Triphosphate)** is called the "energy currency" of the cell because it serves as the universal intermediate that transfers energy between energy-releasing reactions (catabolism) and energy-requiring reactions (anabolism). ## Key Features: - Acts like money: earned through breakdown of nutrients, spent on cellular work - Contains high-energy phosphate bonds (~30.5 kJ/mol under standard conditions) - Continuously recycled: ATP → ADP → ATP - Used for muscle contraction, active transport, biosynthesis, etc. ## Worked Example: Glucose Phosphorylation **Reaction needed:** Glucose + Phosphate → Glucose-6-phosphate (G6P) **Direct reaction:** ΔG = +13.8 kJ/mol (unfavorable, won't occur spontaneously) **Using ATP as energy currency:** 1. ATP → ADP + Phosphate: ΔG = -30.5 kJ/mol 2. Glucose + Phosphate → G6P: ΔG = +13.8 kJ/mol **Coupled reaction:** Glucose + ATP → G6P + ADP **Net ΔG = -30.5 + 13.8 = -16.7 kJ/mol** ✓ (favorable!) ATP "pays" for the unfavorable phosphorylation, making it thermodynamically favorable. This is the first step of glycolysis, trapping glucose in the cell.