Changes in the environment will affect the speed in which an enzyme functions.
Temperature is able to speed up and slow down reactions. Usually, when the temperature is very cold, molecules are moving more slowly, and there are less opportunities for an enzyme and substrate to bump into one another. This slows the rate of the reaction and the effect of the enzyme.
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When temperatures increase, molecules move more quickly and bump into one another more frequently. Because of this, the rate of a reaction increases as temperature increases. That is until a specific threshold is hit. Once the temperature becomes too high, the enzyme begins to denature. This occurs when the bonds that hold the amino acids into their 3-dimensional shape begin to break. Once the enzyme loses its shape, it loses its active site and is unable to function.
Therefore, enzymes have an optimal temperature range in which they function. For enzymes that work in the human body, they function best around our body temperature, 97-99 degrees F. When the temperature is too high or too low, the enzymes are not able to perform the life-sustaining reactions that they need to.
pH is a measurement referring to the number of hydrogen ions present in a solution. When there are a lot of hydrogen ions present, the solution has a low pH and is considered acidic. When there is a small number of hydrogen ions present, the solution has a high pH and is considered basic. Every enzyme has an optimal pH where it has its highest activity. A reduction or increase in pH outside of optimal pH leads to the enzyme's activity to slow down and possible denaturation of the enzyme or substrate (leading to a substrate being unable to bind to an active site).
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If the concentration of either is increased, the rate of the reaction should increase, as there is more opportunity for the two to meet. Ideally, both enzyme and substrate concentration would increase, as if only one increases, the other acts as a limiting reagent. This means that the rate of the reaction is limited by the amount of either enzyme or substrate available. An example of a limiting reagent is below.
The concentration of both enzymes and substrates can affect the overall rate of the reaction. A higher concentration of both enzyme and substrate makes it more likely that the two will bump into one another. If either is in low supply, there will be fewer molecules available to start a reaction.
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As described above, there are a number of things that can alter the function of an enzyme, some of which can lead to denaturation. This process can either be temporary or permanent, depending on the magnitude of the damage.
The human body maintains strict ranges of temperature and pH in order to maintain the optimal functioning of enzymes. If the body enters a range that does not support enzyme functioning, such as very high temperature, the enzymes in the body may denature, and the person could die. Thankfully, your body has a number of checks and balances in place to ensure that optimal ranges are continually met.