What is ATP?
ATP (adenosine triphosphate) is the molecule cells use to store and transfer chemical energy. Nearly every cellular process — muscle contraction, active transport, biosynthesis — runs on energy released from ATP. That's why ATP is called the cell's 'energy currency'.
ATP is the nucleotide cells use to store and carry usable energy; hydrolysis of its terminal phosphate bond releases about 30.5 kJ/mol (7.3 kcal/mol) of energy for cellular work.
- 1.Synthesis — Cellular respiration (or photosynthesis) combines ADP + Pi using energy from food or light to build ATP.
- 2.Storage — Energy is stored in the high-energy bonds between ATP's phosphate groups.
- 3.Hydrolysis — The terminal phosphate bond breaks (ATP + H2O → ADP + Pi), releasing about 30.5 kJ/mol.
- 4.Utilization — Released energy powers muscle contraction, active transport, and biosynthesis; ADP + Pi return to be recycled.
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Step-by-step worked examples
A muscle cell hydrolyzes 4 moles of ATP during a contraction. How much energy is released?
Energy = moles × 30.5 kJ/mol Energy = 4 × 30.5 = 122 kJ
A cell needs 610 kJ of energy for an active transport process. How many moles of ATP must be hydrolyzed?
moles = Energy ÷ 30.5 moles = 610 ÷ 30.5 = 20 mol ATP
During protein synthesis, a cell hydrolyzes 0.5 mole of ATP. Calculate the energy released.
Energy = moles × 30.5 kJ/mol Energy = 0.5 × 30.5 = 15.25 kJ
Flashcards
Quick quiz
Q1.What three parts make up an ATP molecule?
Q2.Approximately how much energy is released hydrolyzing 1 mole of ATP?
Q3.What are the products of ATP hydrolysis?
Q4.Why can't cells store large amounts of ATP for later use?
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Common mistakes
ATP is a long-term energy storage molecule like fat. — Correct: ATP is a short-term, immediate energy carrier; fat and glycogen are the long-term storage molecules.
Making ATP requires no oxygen at all. — Correct: The most efficient ATP production (oxidative phosphorylation) requires oxygen; anaerobic pathways make far less ATP.
All three phosphate bonds in ATP release the same energy. — Correct: Mainly the terminal (third) phosphate bond is hydrolyzed for energy release; that's the reaction that yields ~30.5 kJ/mol.
Cells have a huge stockpile of ATP ready to use. — Correct: Cells hold only a tiny ATP reserve and continuously resynthesize it from ADP + Pi as it's used.
FAQ
What is ATP?
ATP (adenosine triphosphate) is the molecule cells use to store and transfer usable chemical energy for nearly all cellular processes.
What is the ATP hydrolysis formula?
ATP + H2O → ADP + Pi + energy, releasing about 30.5 kJ/mol (7.3 kcal/mol).
What are examples of ATP use in cells?
Muscle contraction, active transport across membranes, nerve impulse transmission, and biosynthesis of proteins and DNA all consume ATP.
How do you calculate energy released from ATP?
Multiply the moles of ATP hydrolyzed by about 30.5 kJ/mol, the standard free energy of ATP hydrolysis.