Action of enzymes (CIE A-level Biology)

This fully-resourced lesson describes how enzymes function intracellularly and extracellularly and explains their mode of action. The engaging PowerPoint and accompanying resources have been designed to cover points 3.1 (a, b & c) and considers the details of Fischer’s lock and key hypothesis and Koshland’s induced-fit model and explains how an enzyme’s specificity is related to their 3D structure and enables them to act as biological catalysts.

The lesson has been planned to tie in with topic 2.3, and to challenge the students on their knowledge of protein structure and globular proteins. This prior knowledge is tested through a series of exam-style questions along with current understanding and mark schemes are included in the PowerPoint so that students can assess their answers.

Students will learn that enzymes are large globular proteins which contain an active site that consists of a small number of amino acids. Emil Fischer’s lock and key hypothesis is introduced to enable students to recognise that their specificity is the result of an active site that is complementary in shape to a single type of substrate. Time is taken to discuss key details such as the control of the shape of the active site by the tertiary structure of the protein. The induced-fit model is described so students can understand how the enzyme-susbtrate complex is stabilised and then students are challenged to order the sequence of events in an enzyme-controlled reaction.

The lesson finishes with a focus on ATP synthase and DNA polymerase so that students are aware of these important intracellular enzymes when learning about the details of respiration and DNA replication before they are challenged on their knowledge of carbohydrates, lipids and proteins from topics 1.2 - 1.4 as they have to recognise some extracellular digestive enzymes from descriptions of their biological molecule substrates.