ATP and Biological Energy

This lesson covers the structure and role of adenosine triphosphate (ATP) as the universal energy currency of cells, as required by the Edexcel A-Level Biology B specification (9BI0), Topic 1: Biological Molecules. You need to understand the structure of ATP, how it is synthesised and hydrolysed, and why it is ideally suited to its role as an immediate energy source in living organisms.

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Why Do Cells Need an Energy Currency?

All living cells require energy to carry out their metabolic processes:

• Active transport — moving ions and molecules against their concentration gradient across cell membranes (e.g. sodium–potassium pump)
• Muscle contraction — the sliding filament mechanism requires energy for myosin heads to "power stroke" along actin filaments
• Protein synthesis — assembling amino acids into polypeptides at ribosomes
• Cell division — DNA replication, spindle formation, cytokinesis
• Nerve impulse transmission — re-establishing resting potential via the Na⁺/K⁺-ATPase pump
• Bioluminescence — light production in organisms such as fireflies and deep-sea fish
• Thermoregulation — metabolic heat production in endotherms