Inhibitors & enzyme-catalysed reactions (CIE A-level Biology)

This lesson describes and explains how increasing the concentration of inhibitors affects the rate of an enzyme-catalysed reaction. The PowerPoint and accompanying resource are the last in a series of 4 lessons which cover the content detailed in point 3.2 (a) of the CIE A-level Biology specification but this lesson also covers point 3.2 [c] as competitive and non-competitive inhibitors are introduced and their differing effects on enzyme activity described and explained.

The lesson begins with a made up round of the quiz show POINTLESS called “Biology opposites” and this allows students to recognise that inhibition is the opposite of stimulation. This introduces inhibitors as substances that reduce the rate of a reaction and students are challenged to use their general knowledge of enzymes to identify that inhibitors prevent the formation of the enzyme-substrate complex. Moving forwards, a quick quiz competition generates the abbreviation EIC (representing enzyme-inhibitor complex) and this introduces competitive inhibitors as substances that occupy the active site. The students are asked to apply their knowledge to a new situation to work out that these inhibitors must have a similar shape to the enzyme’s substrate molecule. A series of exam-style questions are used throughout the lesson and at this point, the students are challenged to work out that an increase in the substrate concentration would reduce the effect of a fixed concentration of a reversible competitive inhibitor. The rest of the lesson focuses on non-competitive inhibitors and time is taken to ensure that key details such as the disruption of the tertiary structure is understood and biological examples are used to increase the relevance. Again, students will learn that increasing the concentration of the inhibitor results in a greater inhibition and a reduced rate of reaction but that increasing the substrate concentration cannot reduce the effect as was observed with competitive inhibitors.