Environmental Impacts On Enzyme Function

Question: Because active sites are finely tuned to help a chemical reaction happen, they can be very sensitive to changes in the enzyme's environment. Factors that may affect the active site and enzyme function include:

Answer: -temperature
-pH
-enzyme concentration
-substrate concentration
-regulatory molecules
-cofactors
-compartmentalization
-feedback inhibition

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Question: How does temperature affect enzyme activity?

Answer: A higher temperature makes for higher rates of reaction, enzyme-catalyzed or otherwise, because it increases speed the of movement of molecules in a solution, increasing the frequency of collisions between enzymes and substrates.

However, extreme high temperatures can cause an enzyme to lose its shape (denature) and stop working.

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Question: How does pH affect enzyme activity?

Answer: Environmental pH can alter the efficiency of enzyme activity, including through disruption of hydrogen bonds that provide enzyme structure.

Each enzyme has an optimum pH range. Changing the pH outside of this range will slow enzyme activity. Extreme pH values can cause enzymes to denature.

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Question: How does enzyme concentration affect enzyme activity?

Answer: Increasing enzyme concentration will speed up the reaction, as long as there is substrate available to bind to. Once all of the substrate is bound, the reaction will no longer speed up, since there will be nothing for additional enzymes to bind to.

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Question: How does substrate concentration affect enzyme activity?

Answer: Increasing substrate concentration also increases the rate of reaction to a certain point. Once all of the enzymes have bound, any substrate increase will have no effect on the rate of reaction, as the available enzymes will be saturated and working at their maximum rate.

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Question: How do changes to the structure of an enzyme affect its function?

Answer: Change to the molecular structure of a component in an enzymatic system may result in a change of the function or efficiency of the system—
a. Denaturation of an enzyme occurs when the protein structure is disrupted, eliminating the ability to catalyze reactions.
b. Environmental temperatures and pH outside the optimal range for a given enzyme will cause changes to its structure, altering the efficiency with which it catalyzes reactions.
In some cases, enzyme denaturation in reversible, allowing the enzyme to regain activity

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Question: pH=-log[H+]

Answer: formula for pH

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Question: competitive inhibitor molecules

Answer: can bind reversibly or irreversibly to the active site of the enzyme, so new substrates cannot bind there and the enzyme does not catalyze any new reaction from that active site
If an inhibitor is competitive, it will decrease reaction rate when there's not much substrate, but can be "out-competed" by lots of substrate.

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Question: allosteric competitive inhibition

Answer: can bind reversibly or irreversibly to an allosteric site of the enzyme, so the enzyme cannot catalyze any new reaction; its competitive, if the substrate binds first, then the allosteric competitive inhibitor cannot bind with enzyme. Likewise, if the allosteric competitive inhibitor binds first, then the substrate can't bind

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Question: allosteric site

Answer: The place on an enzyme where a molecule that is not a substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active.

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Question: noncompetitive inhibition

Answer: In noncompetitive inhibition, the inhibitor binds with the enzyme at a site other than the active site and inactivates the enzyme by altering its shape. It's not competitive, because the inhibitor and the substrate can both bind to the enzyme.
If an inhibitor is noncompetitive, the enzyme-catalyzed reaction will never reach its normal maximum rate even with a lot of substrate. This is because the enzyme molecules with the noncompetitive inhibitor bound are "poisoned" and can't do their job, regardless of how much substrate is available.

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Question: How do regulatory molecules affect enzyme activity?

Answer: Inhibitors decrease enzyme activity.
Types include noncompetitive and competitive inhibition and are explained elsewhere
Activators are molecules that increase enzyme activity..

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Question: allosteric regulation of enzymes

Answer: may either inhibit or stimulate an enzyme's activity; occurs when a regulatory molecule binds to a protein at one site and affects the protein's function at another site

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Question: allosteric enzymes

Answer: -enzymes that are allosterically regulated
-typically have multiple active sites located on different protein subunits
-when an allosteric inhibitor binds to an enzyme, all active sites on the protein subunits are changed slightly so that they work less well
-when an allosteric activator binds to locations on an enzyme other than the active site, it causes an increase in the function of the active site
-in cooperativity, the substrate itself can serve as an allosteric activator: when it binds to one active site, the activity of the other active sites goes up. This is considered allosteric regulation because the substrate affects active sites far from its binding site.

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Question: cooperativity (regarding enzymes)

Answer: the substrate itself serves as an allosteric activator: when it binds to one active site, the activity of the other active sites goes up. This is considered allosteric regulation because the substrate affects active sites far from its binding site.

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Question: Cofactors

Answer: Any nonprotein molecule or ion that is required for the proper functioning of an enzyme. Cofactors can be permanently bound to the active site or may bind loosely with the substrate during catalysis. For example, the enzyme that builds DNA molecules, DNA polymerase, requires magnesium ions to function.

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Question: Coenzymes

Answer: An organic molecule that is a necessary participant in some enzymatic reactions; helps catalysis by donating or accepting electrons or functional groups; e.g., a vitamin, ATP, NAD+.

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Question: Enzyme compartmentalization

Answer: the storing of enzymes in specific parts of cells, (like lysosomes), because it
-prevents competing reactions from interfering
-allows for simultaneous pathways
-allows for precise regulation

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Question: feedback inhibition

Answer: A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.

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Question: How does ATP work as a feedback inhibitor, while ADP acts as an activator?

Answer: ATP is an allosteric inhibitor of some of the enzymes involved in cellular respiration. When there is lots of ATP, this feedback inhibition stops more from being created.
ADP, on the other hand, serves as a positive allosteric regulator (an allosteric activator) for some of the same enzymes that are inhibited by ATP. For instance, ADP may act by binding to an enzyme and changing its shape so that it becomes more active.
Thanks to this pattern of regulation, when ADP levels are high compared to ATP levels, cellular respiration enzymes become very active and will make more ATP through cellular respiration.

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Question: enzyme kinetics

Answer: the study of the rate of formation of products from substrates in the presence of an enzyme

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Question: initial velocity (V0)

Answer: The initial rate of an enzymatic or chemical reaction at the very beginning of the reaction.

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Question: Enzyme saturation

Answer: occurs when substrate levels are so high that all enzyme molecules are actively engaged in the chemical reaction, and so further increases in substrate concentration do not increase reaction rate.

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Question: maximum velocity (Vmax)

Answer: the highest rate of an enzyme-catalyzed reaction , occurring when the enzyme is saturated with substrate

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Question: The substrate concentration that gives you a rate that is halfway to Vmax is called Km and is a useful measure of

Answer: how quickly reaction rate increases with substrate concentration. Km is also a measure of an enzyme's affinity for (tendency to bind to) its substrate. A lower Km corresponds to a higher affinity for the substrate, while a higher Km corresponds to a lower affinity. Although Vmax depends on enzyme concentration, Km always the same for a particular enzyme characterizing a given reaction (although it can be altered by inhibitors)

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Question: With a competitive inhibitor, the reaction can eventually reach its normal Vmax, but it takes a higher concentration of substrate to get it there. In other words, Vmax is unchanged, but the apparent Km is higher. Why must more substrate be added in order to reach Vmax?

Answer: The extra substrate makes the substrate molecules abundant enough to consistently "beat" the inhibitor molecules to the enzyme.

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Question: Why can a reaction never reach its normal Vmax with a noncompetitive inhibitor, regardless of how much substrate is added?

Answer: A subset of the enzyme molecules will always be "poisoned" by the inhibitor, so the effective concentration of enzyme (which determines Vmax) is reduced. However, the reaction reaches half of its new Vmax at the same substrate concentration, so Km is unchanged, which reflects that inhibitor doesn't affect binding of enzyme to substrate, just lowers the concentration of usable enzyme.

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Question: Michaelis-Menten equation

Answer: Describes the kinetics of simple one-substrate reactions.

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Question: switch-like response enzyme kinetics

Answer: Allosteric enzymes typically have multiple active sites and often display cooperativity, meaning that the binding of a substrate at one active site increases the ability of the other active sites to bind and process substrates. This results in a "switch-like" transition low to high reaction rate as substrate concentration increases. This corresponds to a velocity vs. substrate curve that is S-shaped.

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