Enzymes and investigations, at a glance

An enzyme binds suitable substrates at an active site and lowers activation energy. Products leave and the enzyme can catalyse another reaction.

• Specificity includes shape and chemical compatibility.
• Induced fit involves conformational adjustment.
• The overall reactant-product energy difference remains unchanged.

Keep in mind: It lowers the activation-energy requirement. It does not act as the fuel that supplies the reaction's energy.

Temperature affects molecular motion and enzyme stability; pH affects charges and interactions. Rate reflects productive binding under the particular conditions.

• Temperature changes both kinetics and protein stability.
• pH changes ionisation and interactions.

Keep in mind: Low temperature usually slows motion and reaction reversibly. High-temperature loss of folding is a different mechanism.

More substrate increases productive encounters until available active sites become limiting. More enzyme adds active sites if enough substrate is available.

• A substrate plateau indicates limited catalytic capacity.
• Enzyme concentration affects initial rate most clearly when substrate is in excess.

Keep in mind: At saturation the enzyme is working near its maximum rate; active sites are occupied much of the time.

Define the rate measure, change one factor, control other conditions and use repeats to judge reliability. A model activity prepares you for an investigation; it is not laboratory proficiency.

• Rate needs a change divided by time with appropriate units.
• 1/time is a relative endpoint measure.
• Repeats do not automatically remove systematic error.

Keep in mind: Repeats help assess random variation, but a consistent leak can keep underestimating gas. Fix and check the apparatus to address that bias.