Topic 3) Enzymes (AS)

🧬 Topic 3: Enzymes

3.1 Mode of Action of Enzymes

• Enzyme-Substrate Specificity

  • Enzymes are highly specific to their substrates due to the unique shape and chemical properties of their active sites.

  • This specificity ensures that enzymes catalyze only particular reactions.A Level Biology+2TutorChase+2A Level Biology+2

• Lock and Key Model

  • The substrate fits precisely into the enzyme's active site, forming an enzyme-substrate complex.

  • This model suggests that the enzyme's active site is a perfect match for the substrate.

• Induced Fit Model

  • The enzyme's active site undergoes a conformational change upon substrate binding, enhancing the fit between enzyme and substrate.

  • This model accounts for the flexibility of enzymes and their ability to catalyze reactions effectively.

• Lowering Activation Energy

  • Enzymes lower the activation energy required for a reaction to occur, thereby increasing the rate of reaction.

  • They achieve this by stabilizing the transition state and providing an alternative reaction pathway. Save My Exams

• Enzyme-Substrate Complex Formation

  • The enzyme binds to the substrate to form an enzyme-substrate complex.

  • This complex undergoes a reaction to form products, which are then released, regenerating the enzyme.

3.2 Factors Affecting Enzyme Activity

• Temperature

  • Increasing temperature generally increases the rate of enzyme-catalyzed reactions by providing more kinetic energy.

  • However, temperatures above the enzyme's optimum can lead to denaturation, where the enzyme's structure is altered, reducing its activity.

  • Most human enzymes have an optimum temperature around 37–40°C. TutorChase+1studylib.net+1studylib.net

• pH

  • Each enzyme has an optimum pH at which it functions most efficiently.

  • Deviations from this optimum pH can lead to decreased activity or denaturation.

  • For example, pepsin in the stomach operates best at a low pH (~2), while trypsin in the small intestine functions optimally at a higher pH (~8). A Level Biology+4Study Rocket+4A Level Biology+4A Level Biology

• Substrate Concentration

  • Increasing substrate concentration increases the rate of reaction, up to a point.

  • Once all enzyme active sites are occupied (saturation point), adding more substrate does not increase the reaction rate.Study Rocket+1studylib.net+1

• Enzyme Concentration

  • Increasing enzyme concentration increases the rate of reaction, provided there is an excess of substrate.

  • At higher enzyme concentrations, more enzyme-substrate complexes can form, speeding up the reaction.

• Inhibitors

  • Competitive Inhibitors

    • Resemble the substrate and compete for binding to the enzyme's active site.

    • Their presence can decrease the rate of reaction by reducing the number of available active sites.

  • Non-Competitive Inhibitors

    • Bind to an allosteric site (a site other than the active site) on the enzyme.

    • This binding alters the enzyme's shape, reducing its activity even if the substrate can still bind.

• Coenzymes and Cofactors

  • Coenzymes are organic molecules, often derived from vitamins, that assist enzymes in catalyzing reactions.

  • Cofactors are inorganic ions, such as metal ions, that bind to enzymes and are essential for their activity.

  • Both coenzymes and cofactors are necessary for the proper functioning of many enzymes.