5.4 Catalysis and Enzyme Action

Catalysis is the secret sauce of chemical reactions, speeding things up without getting used up. It's like a matchmaker for molecules, bringing them together and making magic happen faster. Enzymes take this to the next level in living things.

These protein powerhouses are nature's catalysts, working their magic in our bodies. They're super picky about what they work with and can be turned on or off like a light switch. Understanding enzymes is key to grasping how life ticks at the molecular level.

Fundamentals of Catalysis

Catalysis and reaction acceleration

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• Catalysis increases reaction rate without being consumed lowers activation energy provides alternative reaction pathway
• Accelerates chemical reactions increases rate of product formation allows reactions under milder conditions (lower temperature, pressure) maintains equilibrium position
• Catalysts facilitate catalysis remain unchanged after reaction can be reused multiple times (industrial processes)

Homogeneous vs heterogeneous catalysis

• Homogeneous catalysis occurs with catalyst and reactants in same phase usually liquid phase (acid-catalyzed esterification)
• Heterogeneous catalysis involves catalyst and reactants in different phases typically solid catalyst with liquid or gas reactants (catalytic converters, Haber process)
• Differences: heterogeneous easier to separate homogeneous often uses milder conditions homogeneous generally more selective
• Similarities: both increase reaction rate neither affect reaction equilibrium

Enzyme Catalysis

Enzymes as biological catalysts

• Proteins with specific 3D shapes composed of amino acid chains often contain cofactors or prosthetic groups (heme in hemoglobin)
• Catalyze biochemical reactions in living organisms highly specific for particular substrates operate under physiological conditions (body temperature, neutral pH)
• Characteristics: high catalytic efficiency (lysozyme) recyclability regulation through cellular mechanisms (allosteric regulation)

Enzyme structure and function

• Enzyme specificity: lock-and-key model perfectly fits substrate induced fit model shape changes upon substrate binding
• Active sites: specific region where catalysis occurs composed of amino acid residues determines enzyme's catalytic properties
• Substrate binding: forms enzyme-substrate complex involves weak interactions (hydrogen bonds, van der Waals forces) orients substrate for reaction

Factors affecting enzyme activity

• pH effects: optimal pH range for each enzyme affects ionization state of amino acid residues extreme pH denatures enzymes (pepsin in stomach acid)
• Temperature effects: increased temperature raises reaction rate up to optimum excessive heat denatures enzymes cold temperatures slow activity
• Inhibitors: competitive inhibitors bind active site (penicillin) non-competitive inhibitors bind elsewhere change enzyme shape irreversible inhibitors permanently modify enzyme
• Other factors: substrate concentration follows Michaelis-Menten kinetics enzyme concentration directly proportional to reaction rate presence of cofactors or coenzymes (NAD+ in dehydrogenases)