3.6.5 Explain the use of lactase in the production of lactose-free milk.
Aim 8: Production of lactose-free milk is an example of an industrial process depending on biological methods (biotechnology). These methods are of huge and increasing economic importance.
Int/TOK: Development of some techniques benefits particular human populations and not others because of the natural variation in human characteristics. Lactose intolerance is found in a high proportion of the human population (for example, in Asia) but more rarely among those of European origin. Sometimes a transfer of biotechnology is needed when techniques are developed in one part of the world that are more applicable in another.
7.6.2 Describe the induced-fit model.
This is an extension of the lock-and-key model. Its importance in accounting for the ability of some enzymes to bind to several substrates should be mentioned.
TOK: Scientific truths are often pragmatic. We accept them as true because they give us predictive power, that is, they work. The German scientist Emil Fischer introduced the lock-and-key model for enzymes and their substrates in 1890. It was not until 1958 that Daniel Koshland in the United States suggested that the binding of the substrate to the active site caused a conformational change, hence the induced-fit model. This is an example of one model or theory, accepted for many years, being superseded by another that offers a fuller explanation of a process.
3.6.1 Define enzyme and active site.
3.6.2 Explain enzyme–substrate specificity.
The lock-and-key model can be used as a basis for the explanation. Refer to the three dimensional structure. The induced-fit model is not expected at SL.
3.6.3 Explain the effects of temperature, pH and substrate concentration on enzyme activity.
Aim 7: Enzyme activity could be measured using data loggers such as pressure sensors, pH sensors or colorimeters.
Aim 8: The effects of environmental acid rain could be discussed.
3.6.4 Define denaturation.
Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties. Refer only to heat and pH as agents.
ADVANCED HIGHER LEVEL: Enzymes [2h]
STANDARD LEVEL OPTION: C.1
7.6.1 State that metabolic pathways consist of chains and cycles of enzyme catalysed reactions.
7.6.4 Explain the difference between competitive and non-competitive inhibition, with reference to one example of each.
Competitive inhibition is the situation when an inhibiting molecule that is structurally similar to the substrate molecule binds to the active site, preventing substrate binding.
Limit non-competitive inhibition to an inhibitor binding to an enzyme (not to its active site) that causes a conformational change in its active site, resulting in a decrease in activity.
Reversible inhibition, as compared to irreversible inhibition, is not required.
7.6.3 Explain that enzymes lower the activation energy of the chemical reactions that they catalyse. Only exothermic reactions should be considered. Specific energy values do not need to be recalled.
7.6.5 Explain the control of metabolic pathways by end-product inhibition, including the role of allosteric sites.