Biochemistry: Enzymes and Catalysts

Enzymes as Remarkable Catalysts

• Enzymes speed up biochemical reactions.
• Most enzymes are proteins, some are RNAs.
• Enzymes stabilize the transition state (highest energy state in reaction).
• Enzymes function optimally at specific temperatures and pH levels.

Enzymes Catalyze Highly Specific Reactions

• Reactants in enzyme-catalyzed reactions are called substrates.
• Enzymes are highly specific, like proteolytic enzymes that hydrolyze peptide bonds between amino acids.

Proteases Break Peptide Bonds

• Proteases readily break peptide bonds.

Enzyme Cofactors

• Many enzymes require cofactors (non-protein molecules or ions) for activity.
• Coenzymes and metals are two main cofactor classes.
• A holoenzyme is an enzyme with its cofactor; an apoenzyme lacks a cofactor.

Active Sites of Enzymes

• Enzymes have catalytic and binding sites.
• The catalytic site is where the reaction occurs.
• The binding site (active site) is where substrates bind, forming an enzyme-substrate complex.
• Binding is highly specific, promoting the catalytic reaction. (Lock-and-key and induced-fit models illustrate this).

Thermodynamics and Enzymes

• Gibbs Free Energy (G) is a useful thermodynamic function.
• The change in Gibbs Free Energy (ΔG) indicates if a reaction will proceed forward or backward.
• ΔG depends only on the free energy difference between reactants and products.
• ΔG does not indicate the speed of the reaction.

Enzyme Rate Acceleration

• Enzymes accelerate the reaction rate but do not change the equilibrium point. Reaction will proceed to equilibrium quickly with an enzyme.

Michaelis-Menten Kinetics

• Describes enzyme kinetics.
• Km = Michaelis-Menten constant (a substrate concentration), and Vmax=maximum reaction rate.
• kcat = turnover number showing catalytic efficiency of the enzyme (kcat/Km).
• Plots (Lineweaver-Burk/Eadie-Hofstee) used to analyze the data for Km and Vmax

Allosteric Regulation

• Allosteric enzymes have multiple active sites on different protein subunits.
• Allosteric activators increase enzyme activity.
• Allosteric inhibitors decrease enzyme activity.
• Cooperativity = substrate can act as an allosteric activator
• Enzyme inhibitors or activators bind to an allosteric site and not the active site

Enzyme Inhibition

• Competitive inhibition: inhibitor competes with substrate for active site.
• Noncompetitive inhibition: inhibitor binds to an allosteric site, reducing overall enzyme efficiency.

Examples of Enzymes

• Examples of enzymes that follow Michaelis-Menten kinetics or not, like proteases (e.g., chymotrypsin) and others. (e.g., Phosphofructokinase, glycogen phosphorylase) given for reference

Explore the fascinating world of enzymes in this quiz! Learn how these remarkable catalysts speed up biochemical reactions, their specificity in substrate interaction, and the role of cofactors. Test your knowledge on active sites, proteases, and the nuances of enzyme function.