Enzymes as Proteins

Enzymes as Proteins

• Definition: Enzymes are biological catalysts that are primarily composed of proteins.

Structure of Proteins

• Levels of Structure:

  • Primary Structure:

    • Linear arrangement of amino acids linked by peptide bonds.

  • Secondary Structure:

    • Formation of alpha helices and beta-pleated sheets stabilized by hydrogen bonds.

  • Tertiary Structure:

    • Three-dimensional folding of a single polypeptide chain into a functional configuration.

  • Quaternary Structure:

    • Complex formation of multiple polypeptide chains (subunits) to form a functional enzyme.

Active Site and Catalysis

• Active Site:

  • Specific region of the enzyme where substrate binding occurs and catalysis takes place.

  • Enzymes lower the activation energy needed for reaction, enabling substrates to be converted into products efficiently.

Enzyme Characteristics

• Activation Energy:

  • All reactions require a certain amount of input energy to commence, known as activation energy.

  • Enzymes reduce the activation energy needed, allowing reactions to occur more readily and at lower energy levels.

• Substrates and Examples:

  • The specific reactants that enzymes act upon; e.g., amylase acts on starch, where starch is the substrate.

Induced Fit Hypothesis

• Induced Fit vs. Lock and Key:

  • Lock and Key Model: Substrate fits perfectly into the active site without modification.

  • Induced Fit Model: When the substrate enters the active site, it causes a change in shape to allow a tighter fit, facilitating the conversion to product.

Temperature Effects on Enzyme Activity

• Temperature Influence:

  • Low temperatures render enzymes inactive.

  • Optimal temperature (e.g., 37°C for human enzymes) increases enzyme activity.

  • Beyond optimal temperature, enzymes denature, losing their functional shape and thereby their activity.

pH Effects on Enzyme Activity

• pH Influence:

  • Each enzyme has its optimal pH for activity (e.g., pepsin operates best at pH 2 in the stomach, while others require alkaline conditions).

  • Deviation from optimal pH can lead to denaturation, ceasing their activity.

  • Bile neutralizes stomach acidity for enzyme function in the small intestine.

Inhibition of Enzyme Activity

• Competitive Inhibition:

  • A competitor substance binds to the active site, preventing substrate from accessing it, thus hindering reaction.

  • Increasing substrate concentration can overcome this inhibition.

• Non-competitive Inhibition:

  • An inhibitor binds to a site other than the active site, altering the shape of the enzyme and its active site, preventing substrate binding.

  • This type of inhibition cannot be overcome by increasing substrate concentration.

Conclusion

• Understanding enzymes is crucial in biochemistry, as they play vital roles in facilitating biological reactions by lowering activation energy and exhibiting specific structural adaptations that determine their function.