Enzyme Notes
What are Enzymes?
Enzymes: biological catalysts (proteins).
Speed up reactions, lower activation energy.
Made of amino acids in 3D shapes.
Characteristics of Enzymes
Active site for substrate binding.
Globular proteins with catalytic properties.
Mostly tertiary/quaternary structures.
Active site: reaction occurs, specific amino acids.
Reactions are reversible.
Not consumed, can be reused.
Highly specific to substrates.
Very efficient in small amounts.
Affected by pH, temp, substrate/enzyme concentration, inhibitors, activators.
Metabolism
Total of all cell chemical reactions.
Anabolism
Simpler to complex substances.
Requires energy (endergonic).
Ex: Glycogen synthesis from glucose.
Catabolism
High to low energy substances.
Complex to simpler substances.
Releases energy (exergonic).
Ex: Glycogen hydrolysis into glucose.
Exergonic and Endergonic Reactions
Exergonic
Energy released.
Delta G negative (\triangle G < 0).
Endergonic
Energy required.
Delta G positive (\triangle G > 0).
\triangle G = [E \text{ of product}] – [E \text{ of reactant}]
Enzymes and Activation Energy
Lower activation energy, speed up reactions.
Reactions: forming/breaking bonds.
Activation energy: initial input for bonds to break/form.
Enzymes speed up reactions in the same direction.
Mechanism of Enzyme Action
Bind substrates to active site.
Active site: specific region for substrate combination.
Unique geometric shapes.
Lock and Key Theory
Enzyme (lock), substrate (key).
Correct key fits the lock.
Fixed, rigid active site.
Induced-Fit Theory
Substrate changes enzyme conformation.
Active site molded to precise conformation.
Flexible active site.
Enzyme returns to original shape after product release.
Factors Affecting Enzyme Activity
pH
Optimum pH for maximal activity.
Influences charges, ions, bonding.
Changes above/below optimum pH decrease rate.
Temperature
Below optimum: Insufficient kinetic energy.
At optimum: Increased kinetic energy.
Above optimum: Enzyme denatures.
Enzyme Concentration
Low concentration: high competition, low rate.
Increased concentration: increases rate if substrate sufficient.
Substrate Concentration
Rate increases until saturation.
No significant change after saturation.
Cofactors
Non-protein components that assist enzyme function.
Can bind permanently/reversibly.
Types of Cofactors
Coenzymes: Organic, loosely attached (e.g., NAD).
Prosthetic Groups: Organic, firmly attached (e.g., FAD).
Metal Ions: Inorganic (e.g., K^+, Zn^{2+}, Mg^{2+}).
Enzyme components
Holoenzyme: enzyme + cofactor, active
Apoenzyme: enzyme without cofactor, inactive
Inhibitors
Decrease enzyme activity.
Reversible Inhibition
Weak bonds, easily removed (e.g., ibuprofen).
Irreversible Inhibition
Tight, covalent bonds, chemical changes.
Types of Reversible Inhibitors
Competitive Inhibition
Substrate/inhibitor compete for active site.
Overcome by increasing substrate.
Non-Competitive Inhibition
Inhibitor binds to allosteric site, changes enzyme shape.
Cannot be overcome by increasing substrate.
Non-Competitive Irreversible Inhibition
Inhibitor has strong covalent bonds at allosteric site.
Causes permanent damage (e.g., Arsenic).
Allosteric Regulation
Regulatory molecules bind at allosteric site, altering enzyme shape.
Inhibitors cause inactive shape.
Activators promote active shape.
Allosteric Inhibition
Inhibitor binding switches enzyme between active/inactive configurations.
Substrate cannot fit when inhibitor is present.
Feedback Inhibition
End product inhibits early reaction in pathway.
Pathway switches off.
End product: non-competitive reversible inhibitor.
Naming and Classification of Enzymes
Names indicate substrate and reaction type (-ase suffix).
Six Classes of Enzymes
**Oxidore