Biochemistry Chapter on Enzymes

Enzymes Overview

• Enzymes are proteins that act as biological catalysts, accelerating biochemical reactions significantly.
• They exhibit high specificity, catalyzing either a single reaction or closely related reactions.

Properties of Enzymes

• Enzymes are globular proteins with a three-dimensional shape that determines function.
• They lower the activation energy needed for reactions, thus speeding up the process without being consumed.
• Each enzyme has an active site specific to its substrate, where the conversion of substrates to products occurs.

Mechanism of Enzyme Action

• Carbonic anhydrase demonstrates enzyme efficiency, accelerating the reaction from CO2 and H2O to H2CO3 from 0.13 to 1,000,000 molecules per second.
• The active site, a small cluster of amino acids, creates a microenvironment for substrate binding and catalysis.

Enzyme Specificity and Affinity

• Specificity refers to an enzyme's ability to preferentially bind to a specific substrate.
• Affinity measures the strength of the binding interaction between enzyme and substrate.

Enzyme Sensitivity and Optimal Conditions

• Enzymes operate best under optimal conditions regarding temperature, pH, and salt concentration.
• Variability in enzyme sensitivity impacts their effectiveness across different environments.

Catalytic Process

• Enzymes facilitate the formation of a transition state through the formation of an enzyme-substrate complex (ES).
• They change the reaction rate but not the reaction itself.

Enzyme Kinetics

• Michaelis-Menten kinetics studies the relationship between substrate concentration and reaction velocity (V0).
• Vmax indicates the maximum reaction rate achieved by an enzyme at saturation point when most active sites are occupied.
• The Michaelis-Menten constant (KM) defines substrate concentration required for half-maximal velocity, indicating binding strength.

Enzymes and Cofactors

• Many enzymes, known as holoenzymes, require cofactors for activity.
• Cofactors can be organic (coenzymes like vitamins) or inorganic (metal ions such as Zn2+).
• Apoenzymes refer to the inactive protein portion of an enzyme without its cofactor.

Allosteric Regulation

• Allosteric enzymes possess multiple binding sites; substrate binding can influence the activity of other sites.
• They do not follow simple Michaelis-Menten kinetics and often exhibit a sigmoidal reaction rate curve.

Classification of Enzymes

• Enzymes are classified based on the reaction type they catalyze and commonly end in "ase."
• Major classes include:
  • Oxidoreductases: Involved in oxidation-reduction reactions (e.g., alcohol dehydrogenase).
  • Transferases: Transfer functional groups between molecules (e.g., glycerokinase).
  • Isomerases: Rearrange functional groups within a molecule (e.g., maleate isomerase).
  • Hydrolases: Catalyze hydrolytic cleavage (e.g., carboxypeptidase A).
  • Lyases: Add or remove groups form molecules (e.g., pyruvate decarboxylase).
  • Ligases: Join two molecules together (e.g., pyruvate carboxylase).

This quiz covers the specificity and binding affinities of enzymes, focusing on endopeptidases and exopeptidases. Test your knowledge on the structure and function of various enzymes, including pepsin, chymotrypsin, and trypsin. Gain a deeper understanding of enzyme kinetics and peptide bonds.