AP Syllabus focus:
‘Higher temperatures increase molecular movement and enzyme–substrate collisions, raising reaction rates until the optimal temperature is exceeded.’
Temperature is a major factor controlling how fast enzyme-catalysed reactions proceed in cells. Understanding why reaction rate rises with warming—and why it eventually drops—helps explain cellular performance limits.
Core idea: temperature changes collision frequency and energy
Enzyme-catalysed reactions depend on random molecular collisions between enzyme and substrate in solution. Temperature affects:
Molecular movement: warmer molecules move faster.
Collision frequency: faster movement increases how often enzyme and substrate collide.
Collision quality: a higher fraction of collisions have enough energy to form product.
Kinetic energy and successful collisions
Practice Questions
FAQ
They have structural features that increase stability, such as more ionic interactions and hydrophobic packing.
This reduces loss of functional shape at high temperature, shifting the optimum upward.
Different proteins have different amino acid sequences and stability.
Local cellular environments (e.g., compartments with different solute concentrations) can also shift the temperature at which each enzyme performs best.
Cells can alter which enzyme isoforms are expressed and change membrane composition and solute concentrations.
These shifts can change effective enzyme performance across temperatures over days to weeks.
Immediately, faster molecular movement can boost collisions and rate.
Over time, the fraction of enzyme molecules in a functional conformation can decrease, reducing measured rate during longer incubations.
Allowing temperature to drift during the assay
Using unequal equilibration times at each temperature
Evaporation changing concentrations at higher temperatures
Measuring at temperatures where substrate becomes limiting, masking true temperature dependence
