C1.2.1 – ATP as the Molecule That Distributes Energy Within Cells
Adenosine Triphosphate (ATP) is a universal energy carrier in all living organisms. It is a
nucleotide composed of:
● Adenine (a nitrogen-containing base)
● Ribose (a five-carbon sugar)
● Three phosphate groups, with high-energy bonds between them
Why ATP is Ideal for Energy Transfer:
● The bond between the second and third phosphate is unstable and easily broken by
hydrolysis, releasing energy efficiently.
● ATP is small and water-soluble, allowing rapid diffusion to parts of the cell where
energy is needed.
● The breakdown of ATP is a single-step reaction:
ATP + H₂O → ADP + Pi + energy
● Energy released is sufficient to drive cell reactions but not so large as to generate
waste heat.
● ATP can be quickly regenerated from ADP + Pi using energy from respiration.
C1.2.2 – Life Processes That ATP Supplies With Energy
ATP is required for nearly every endothermic (energy-consuming) process in cells:
1. Anabolic Reactions (Biosynthesis):
○ Polymerization of amino acids to form proteins
○ DNA replication, RNA transcription
○ Synthesis of polysaccharides (e.g., starch, glycogen)
2. Active Transport:
○ Movement of ions and molecules across membranes against concentration
gradients
○ Example: Na⁺/K⁺ pump in neurons; H⁺ pumps in mitochondria and chloroplasts
3. Cellular Movement and Work:
○ Muscle contraction (interaction of actin and myosin filaments)
○ Chromosome movement during mitosis (spindle fiber formation)
○ Cytoplasmic streaming and organelle transport
○ Cilia and flagella beating
4. Signal Transduction and Regulation:
○ Phosphorylation of proteins to activate/deactivate enzymes or pathways
C1.2.3 – Energy Transfers During ATP ↔ ADP Interconversion
ATP is constantly synthesized and hydrolyzed in living cells, creating a dynamic equilibrium:
● Hydrolysis (exergonic): Releases ~30.5 kJ/mol of energy
○ ATP → ADP + Pi + energy
● Phosphorylation (endergonic): Requires energy input from respiration
