Notes on Proteins and Enzymes

  • Introduction to Proteins and Enzymes

    • Discussed the relationship between metabolism and energy transformations.
    • Metabolism involves endogenic (requiring energy) and exogenic (releasing energy) reactions.
    • First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.
    • Second Law of Thermodynamics: Energy transformations increase entropy (disorder). Loss of energy occurs in the form of heat during reactions.

  • Reactions Coupling

    • Anabolic processes (e.g., DNA synthesis) are endogenic and require energy input.
    • Coupling of these with exogenic reactions (like ATP breakdown) helps to drive them forward.

  • Enzymes in Metabolism

    • Enzymes speed up reactions without being consumed in the process.
    • Example: Hydrolysis of sucrose (disaccharide) into glucose and fructose is spontaneous but slow without intervention.
    • Sucrase, the enzyme for sucrose breakdown, exemplifies the naming convention (ASE = enzyme).

  • Activation Energy

    • Enzymes lower the activation energy (the energy required to initiate a reaction) facilitating faster reactions.
    • Comparison of spontaneous exergonic reactions demonstrates that activation energy can be reduced with the help of enzymes.
    • Analogy: Jumping off a diving board to release energy.

  • Characteristics of Enzymes

    • Enzymes are proteins, known as molecular catalysts, which facilitate biochemical reactions.
    • High specificity: Enzymes typically act on specific substrates (i.e., sucrase acts on sucrose).
    • Induced Fit Model: Enzymes mold their structure to snugly bind with substrates at the active site, as opposed to the rigid "lock and key" model.

  • Factors Affecting Enzyme Activity

    • Substrate concentration: Increased substrate enhances reaction rates until reaching a plateau (limit of enzyme activity).
    • Temperature: Affects kinetic energy of molecules; enzymes have optimal temperatures (e.g. ~37°C for human enzymes).
    • Reaction rates initially increase with temperature, but excessive heat can denature enzymes (destroy function).
    • pH: The acidity or basicity of the environment affects enzyme shape and function; each enzyme has an optimal pH.
    • Example: Pepsin (stomach enzyme) functions optimally at pH 2, while intestinal enzymes may function around pH 8.

  • pH and Enzyme Functionality

    • pH is measured on a scale from 1 (very acidic) to 14 (very basic), with 7 being neutral.
    • It influences binding sites on enzymes and can change their shape and activity.

  • Conclusion

    • Understanding enzymes and factors affecting their activity is crucial for experimental biology and practical applications.
    • Importance of optimal conditions for enzymes to function properly underlining the significance of contextual knowledge in experiments.