Biology A-Level Chapter 3

Summary:

This document covers the mode of action of enzymes and how they work, based on the A Level Biology (9700) exams from 2022.

Enzymes are biological catalysts, which means they speed up chemical reactions in living systems without being consumed or altered in the process. They are also globular proteins, and the active site of an enzyme is crucial for its function as it’s where substrates bind. Virtually every metabolic reaction in living organisms is catalyzed by an enzyme, and enzymes are essential for life to exist. They can function both inside (intracellular) and outside (extracellular) cells.

The mode of action of enzymes is determined by their active site, where specific substrates bind to form enzyme-substrate complexes. This active site has a specific shape to fit a specific substrate, and this specificity is due to the complex tertiary structure of the protein that makes up the enzyme. Proteins are formed from chains of amino acids held together by peptide bonds, and the order of these amino acids determines the shape of an enzyme. If the order is altered, the shape changes.

Enzyme reactions can be either catabolic or anabolic. Catabolic reactions break down complex molecules into simpler products, while anabolic reactions build more complex molecules from simpler ones. Enzymes work by lowering the activation energy of a reaction, providing an alternative energy pathway. Activation energy is the energy needed for the substrate to become unstable enough for a reaction to occur and products to be formed.

Emil Fischer described the first model of enzyme activity in the 1890s. He suggested that enzymes and substrates were rigid structures that locked into each other very precisely, much like a key going into a lock, known as the ‘lock-and-key hypothesis’. This was later modified and adapted to our current understanding of enzyme activity, permitted by advances in the molecular sciences.

Excerpt:

Biology A-Level Chapter 3

3.1 Mode of Action of Enzymes YOUR NOTES

CIE A Level Biology (9700) exams from 2022 Resources

REVISION NOTES, TOPIC QUESTIONS, PAST PAPERS

CONTENTS
3.1.1 Enzymes
3.1.2 Enzyme Action
3.1.3 How Enzymes Work
3.1.4 Measuring Enzyme Activity
3.1.5 Colorimetry