Proteins and enzymes

Nature of science:

Theories can be superseded—“lock and key” hypothesis to “induced fit” model for enzymes. (1.9) Collaboration and ethical considerations—scientists collaborate to synthesize new enzymes and to control desired reactions (ie waste control). (4.5)

• Inhibitors play an important role in regulating the activities of enzymes.
• Amino acids and proteins can act as buffers in solution.
• Protein assays commonly use UV-vis spectroscopy and a calibration curve based on known standards.

Applications and skills:

• Determination of the maximum rate of reaction (V_max) and the value of the Michaelis constant (K_m) for an enzyme by graphical means, and explanation of its significance.
• Comparison of competitive and non-competitive inhibition of enzymes with reference to protein structure, the active site and allosteric site.
• Explanation of the concept of product inhibition in metabolic pathways.
• Calculation of the pH of buffer solutions, such as those used in protein analysis and in reactions involving amino acids in solution.
• Determination of the concentration of a protein in solution from a calibration curve using the Beer–Lambert law.

• Technologies based on enzyme activity go back to ancient times in many parts of the world. Brewing and cheese-making are often associated with particular place names.

Theory of knowledge:

• The term “lock-and-key” is an effective metaphor but the “induced fit” model is a better model. How are metaphors and models used in the construction of knowledge?

Utilization:

• Enzymes are widely used in industrial and domestic applications. Examples include biological detergents, textiles, foods and beverages, and biodegradable plastics. Advances in protein engineering have led to the synthesis of enzymes that are effective in a wide range of conditions.

Syllabus and cross-curricular links:
Topic 6.1—chemical kinetics
Topics 8.1, 8.3 and 8.4—the pH scale and conjugate acids and bases
Topics 18.2 and 18.3—acid–base calculations and pH curves

• The effects of competitive and non-competitive inhibitors on K_m and V_max values should be covered.
• The Henderson–Hasselbalch equation is given in the data booklet in section 1.
• For UV-vis spectroscopy, knowledge of particular reagents and wavelengths is not required.

• Aim 6: Experiments could include measuring enzyme activity with changing conditions of temperature, pH and heavy metal ion concentration.
• Aim 7: Data-logging experiments with temperature or pH probes to investigate enzyme activity under different conditions; or computer modelling of enzyme– substrate interactions.
• Aim 8: Many enzyme technologies help mitigate damaging environmental effects of chemicals, such as from leather, paper and oil industries.