3.2 Environmental Impacts on Enzyme Function
Keywords
| English Term | 中文翻译 | Definition & Explanation |
|---|---|---|
| Denaturation | 变性 | A process in which a protein loses its native shape due to the disruption of weak chemical bonds and interactions, thereby becoming biologically inactive. |
| Optimal Conditions | 最适条件 | The specific range of environmental factors (like temperature and pH) where an enzyme functions at its maximum efficiency. |
| Competitive Inhibitor | 竞争性抑制剂 | A substance that reduces the activity of an enzyme by entering the active site in place of the substrate, whose structure it mimics. |
| Noncompetitive Inhibitor | 非竞争性抑制剂 | A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing the enzyme's shape. |
| Allosteric Site | 别构位点 | A specific receptor site on some part of an enzyme molecule remote from the active site. |
1. Effects of Temperature and pH
Because enzymes are proteins, their complex 3D structures are highly sensitive to their environment. Any change to the molecular structure of a component in an enzymatic system may result in a change to its function or efficiency.
Temperature
- Increasing Rate via Kinetic Energy: Higher environmental temperatures increase the average speed of movement (kinetic energy) of molecules in a solution. This increases the frequency of collisions between enzymes and substrates, therefore increasing the rate of reaction—but only up to a certain point.
- Optimal Temperature: The temperature at which an enzyme works fastest.
- Denaturation at High Temperatures: If the temperature rises beyond the optimal range, the thermal agitation disrupts the hydrogen bonds, ionic bonds, and other weak interactions that stabilize the active site. The enzyme loses its shape (denaturation), eliminating its ability to catalyze reactions.
pH
- Enzymes also have an optimal pH. Environmental pH outside the optimal range will alter the charge of amino acids at the active site and disrupt hydrogen bonds, causing changes to the enzyme's overall structure and decreasing its efficiency.
Reversibility of Denaturation
In some specific cases, enzyme denaturation is reversible. If the harsh environmental conditions (like extreme pH or temperature) are removed and optimal conditions are restored, the protein may fold back into its functional native shape and regain its catalytic activity. However, extreme heat often causes irreversible denaturation (e.g., boiling an egg).
2. Concentrations of Substrates and Products
The relative concentrations of substrates and products in a solution dictate how efficiently an enzymatic reaction proceeds.
- Substrate Concentration: Adding more substrate increases the reaction rate because there are more substrate molecules available to collide with enzyme active sites. However, this rate will eventually level off (plateau) when all available enzyme active sites are occupied (enzyme saturation). At this point, the only way to increase the rate further is to add more enzymes.
3. Enzyme Inhibitors
Certain chemicals can selectively inhibit the action of specific enzymes. If the inhibitor attaches to the enzyme by covalent bonds, the inhibition is usually irreversible. However, many inhibitors bind via weak interactions, making them reversible.
Crucial Detail: Competitive vs. Noncompetitive Inhibition
- Competitive Inhibitors: These molecules resemble the normal substrate molecule and compete for admission into the active site. They reduce productivity by blocking substrates from entering active sites. This kind of inhibition can often be overcome by increasing the concentration of the substrate.
- Noncompetitive Inhibitors: These molecules do not compete with the substrate. Instead, they bind to another part of the enzyme known as the allosteric site. This binding causes the enzyme molecule to change its shape in such a way that the active site becomes less effective or completely nonfunctional.
Quiz
Source: Campbell Biology Practice Test - Chapter 8 (Metabolism & Enzymes)