AP Biology 3.2 Environmental Impacts on Enzyme Function Study Notes - New Syllabus Effective 2025
AP Biology 3.2 Environmental Impacts on Enzyme Function Study Notes- New syllabus
AP Biology 3.2 Environmental Impacts on Enzyme Function Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Explain how changes to the structure of an enzyme may affect its function.
Key Concepts:
- Environmental Impacts on Enzyme Function
3.2.A.1 – Denaturation
Change to the molecular structure of a component in an enzymatic system may result in a change to its function or efficiency.
- Denaturation of proteins, such as enzymes, occurs when the protein structure is disrupted by a change in temperature, pH, or chemical environment, eliminating the ability to catalyze reactions.
- Environmental temperatures and pH outside the optimal range for a given enzyme will cause changes to its structure (by disrupting the hydrogen bonds), altering the efficiency with which it catalyzes reactions.
Denaturation is a process in which proteins lose their quaternary, tertiary and secondary structure. Enzymes must be folded into the right 3D shape to function. But noncovalent interactions, which play a crucial part in protein folding, are individually weak, and it does not take much heat, acidity, or other stress to break some of them and denature the enzyme.
Hence, enzyme catalyzed reactions exhibit an unusual temperature dependence. At relatively low temperatures, the reaction rate increases with temperature, as is expected. However, at higher temperatures, the reaction rate drops dramatically due to denaturation of the enzyme.
3.2.A.2 – Renaturation of enzymes
In some cases, mild denaturation can be reversed if conditions return to normal—often called renaturation. This typically happens if the changes in temperature or pH are not too severe or prolonged, allowing the enzyme to refold into its functional shape. However, many instances of denaturation are permanent, especially when the polypeptide chain becomes irreversibly tangled or fragmented.
3.2.B.1 – Effects of relative concentration of substrate on rate of enzymatic reactions
The rate of enzymatic reactions can be regulated by the relative concentrations of substrates and products through mechanisms such as competitive inhibition, non-competitive inhibition, and feedback regulation. Competitive inhibition occurs when a molecule competes with the substrate for the active site of the enzyme, while non-competitive inhibition involves a molecule binding to a site other than the active site, causing a conformational change in the enzyme. Feedback regulation, specifically negative feedback, controls enzyme activity based on the concentration of products, maintaining an optimal balance of substrates and products within the cell.
3.2.B.2 – Effects of temperature on rate of enzymatic reactions
As temperature increases so do the rate of enzyme reactions. A ten degree centigrade rise in temperature will increase the activity of most enzymes by 50% to 100%. Variations in reaction temperature as small as 1 or 2 degrees may introduce changes of 10% to 20% in the results. This increase is only up to a certain point until the elevated temperature breaks the structure of the enzyme. Once the enzyme is denatured, it cannot be repaired. As each enzyme is different in its structure and bonds between amino acids and peptides, the temperature for denaturing is specific for each enzyme. Because most animal enzymes rapidly become denatured at temperatures above 40°C, most enzyme determinations are carried out somewhat below that temperature.
3.2.B.3 – Competitive Inhibition
Inhibition caused by drugs may be either reversible or irreversible. A reversible situation occurs when an equilibrium can be established between the enzyme and the inhibitory drug. A competitive inhibition occurs when the drug, as “mimic” of the normal substrate competes with the normal substrate for the active site on the enzyme. Concentration effects are important for competitive inhibition.
Probably the easiest type of enzyme inhibition to understand is competitive inhibition and it is the one most commonly exploited pharmaceutically. Molecules that are competitive inhibitors of enzymes resemble one of the normal substrates of an enzyme. An example is methotrexate, which resembles the folate substrate of the enzyme dihydrofolate reductase (DHFR). This enzyme normally catalyzes the reduction of folate, an important reaction in the metabolism of nucleotides. When the drug methotrexate is present, some of the enzyme binds to it instead of to folate and during the time methotrexate is bound, the enzyme is inactive and unable to bind folate. Thus, the enzyme is inhibited. Notably, the binding site on DHFR for methotrexate is the active site, the same place that folate would normally bind. As a result, methotrexate ‘competes’ with folate for binding to the enzyme. The more methotrexate there is, the more effectively it competes with folate for the enzyme’s active site. Conversely, the more folate there is, the less of an effect methotrexate has on the enzyme because folate outcompetes it.
