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3.2.1Additional lessons

Adenosine Triphosphate (ATP) — IB Biology SL Revision Notes & Topical Questions

5 min read 5 parts Lesson 55 of 142

📚 IB Biology SL Hub / Topical Revision
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Part 1 of 5Structure and Cycle

Structure
  • Structure ATP consists of adenine, the sugar ribose and three phosphate groups joined in a chain.
Hydrolysis
  • Hydrolysis Water breaks off the end phosphate to form ADP and inorganic phosphate, releasing energy that the cell can use.
Phosphorylation
  • Phosphorylation The energy released can be transferred by adding the phosphate to another molecule, which makes it more reactive.
Regeneration
  • Regeneration ADP and phosphate are recombined to make ATP using energy released during cell respiration.
Recycling
  • Recycling The ATP and ADP pool is constantly recycled, so a cell holds only a small store of ATP at any moment.

Part 2 of 5Why ATP Is Useful

Why ATP Is Useful
Soluble
  • Soluble ATP is soluble in water, so it moves easily around the cell and into places where energy is needed.
Small packets
  • Small packets Energy is released in amounts small enough to suit most cell reactions, with little wasted as heat.
Fast
  • Fast Hydrolysis is a single, quick reaction, so energy is available immediately.
Stable
  • Stable ATP is stable at the pH of the cell, so it does not break down by itself before it is used.

Part 3 of 5Uses of ATP

1
Active transport uses ATP to move substances across membranes against their concentration gradient.
2
Muscle contraction uses ATP so that protein filaments slide past each other.
3
Synthesis of proteins, DNA and other large molecules uses ATP in anabolic reactions.
4
Nerve cells use ATP to run the sodium-potassium pumps that restore ion gradients.
5
Some energy is lost as heat in every step, which helps to keep warm-blooded animals at body temperature.

Part 4 of 5ATP and Respiration

ATP and Respiration
Link
  • Link Cell respiration releases energy from organic compounds, which is used to make ATP from ADP and phosphate.
Cycle
  • Cycle ATP is used up rapidly, so cells make and break down very large numbers of ATP molecules every day.
Not stored
  • Not stored Cells cannot store large amounts of ATP and make it as needed.

Part 5 of 5Exam Checklist & Tips

3.2.1 – Key Points for the Exam

  • ATP Adenosine triphosphate, the main energy-carrying molecule of cells.
  • ADP Adenosine diphosphate, formed when ATP loses a phosphate group.
  • Hydrolysis A reaction in which a molecule is split using water.
  • Phosphorylation Addition of a phosphate group to a molecule.

Common Mistakes

  • Saying that ATP is a long-term energy store; fats and glycogen store energy for longer.
  • Stating that energy is made by ATP, when energy is transferred and not created.
  • Writing that ATP moves between organisms; it is made and used within each cell.
  • Confusing ADP with AMP or forgetting that ATP has three phosphates.

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