Enzymes Chapter 2

Study Notes

Enzymes are biological catalysts, speeding up reactions in cells.
Enzymes lower the activation energy required for a reaction to occur.
Increasing substrate concentration initially increases reaction velocity, but it plateaus because all enzyme molecules are occupied.
Increasing enzyme concentration increases reaction velocity.
Factors affecting reaction rate include: substrate concentration, enzyme concentration, pH, temperature, and inhibitors.

Substrate Concentration: Increasing substrate concentration speeds up reaction rate initially, until it reaches a saturation point where all enzymes are occupied.
Enzyme Concentration: Increasing enzyme concentration speeds up the reaction rate.
pH: Different enzymes have optimal pH values. Extreme pH values can denature enzymes, causing them to lose their shape and function. Pepsin, for example, works best at a very acidic pH (around 2), while most enzymes function best at a neutral pH (around 7).
Temperature: Enzymes have an optimal temperature for activity. Increasing temperature generally speeds up the rate, up to a point. Beyond this point, the enzyme denatures, and activity slows and stops.
Inhibitors: Substances that decrease the rate of an enzyme-catalyzed reaction.

Reversible Inhibitors: Bind to enzymes through noncovalent bonds. These can often be removed. Examples include drugs and nonpoisons; these can be washed away.
Irreversible Inhibitors: Bind to enzymes through covalent bonds; these cannot be removed. Examples include poisons like lead and cyanide.

Competitive Inhibitors: Structurally similar to the substrate and bind to the active site.
Noncompetitive Inhibitors: Do not resemble the substrate and bind to a different site on the enzyme, changing its shape and hence impacting the enzyme's ability to function.

Allosteric Enzymes: Enzymes whose activity at the catalytic site can be modulated by small molecules (allosteric effectors) binding to a separate site. - Positive allosteric effectors increase enzyme activity. - Negative allosteric effectors decrease enzyme activity.
Isoenzymes: Enzymes catalyzing the same reaction but having different structures. Lactate dehydrogenase (LDH), creatine kinase (CK), and alkaline phosphatase are examples.

Most reactions in cells are catalyzed by enzymes. Enzymes are regenerated during the reaction process.
Enzymes greatly speed up reactions, making them possible at rates compatible with life.
Enzymes can increase reaction rates by thousands of times.

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