Enzyme Kinetics, Catalysis and Inhibition: every key term you need (+ practice quiz)
25 flashcard terms for Biochemistry Topic 4, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
The energy barrier between substrate and transition state. An enzyme lowers it and therefore speeds both directions equally, leaving the equilibrium constant untouched.
Transition state stabilization
The core of enzyme catalysis: the active site binds the strained transition state more tightly than the ground state, which is why transition-state analogues are powerful inhibitors.
Induced fit
The enzyme changes shape on substrate binding to close around it. This improves both catalytic geometry and specificity over a rigid template model.
Active site
The pocket where substrate binds and chemistry happens. It is usually a small fraction of the protein, built from residues distant in sequence but adjacent after folding.
General acid-base catalysis
Active-site residues donate or accept protons at the moment of bond making or breaking, avoiding unstable charged intermediates.
Covalent catalysis
A nucleophilic residue transiently bonds to the substrate, creating an alternative route with a lower barrier and a covalent intermediate that is later resolved.
Metal ion catalysis
A bound metal stabilizes negative charge, orients substrate or activates water as a nucleophile. Zinc and magnesium are the most common in this role.
Catalytic triad
A cooperating set of three residues, classically serine, histidine and aspartate, in which charge relay makes the serine oxygen a far stronger nucleophile.
Oxyanion hole
A pocket of backbone amide hydrogens that hydrogen bonds the developing negative charge of a tetrahedral intermediate, stabilizing the transition state.
Michaelis constant
The substrate concentration giving half maximal velocity. It is a practical measure of the concentration an enzyme is tuned to work at, and only loosely a binding constant.
Maximum velocity
The rate reached when every enzyme molecule is saturated with substrate. It scales directly with total enzyme concentration.
Turnover number
The number of substrate molecules converted per enzyme molecule per second at saturation, obtained by dividing maximum velocity by enzyme concentration.
Catalytic efficiency
The ratio of turnover number to the Michaelis constant, describing performance at low substrate. Its ceiling is set by how fast substrate can diffuse in.
Steady-state assumption
Treats the enzyme-substrate complex concentration as constant during the measured phase, which is what makes the standard rate equation solvable.
Lineweaver-Burk plot
A double reciprocal plot that linearizes kinetic data so intercepts give the kinetic constants. It exaggerates error at low substrate, so it is a diagnostic rather than a fitting method.
Competitive inhibition
The inhibitor binds the free enzyme at the active site. Apparent Michaelis constant rises, maximum velocity is unchanged, and excess substrate overcomes it.
Uncompetitive inhibition
The inhibitor binds only the enzyme-substrate complex, lowering both maximum velocity and the apparent Michaelis constant so their ratio stays fixed.
Mixed inhibition
The inhibitor binds free enzyme and the complex with different affinities, lowering maximum velocity while shifting the Michaelis constant in either direction.
The inhibitor forms a covalent or extremely tight bond, permanently removing enzyme molecules so activity returns only through new synthesis.
Suicide inhibitor
An unreactive compound that the target enzyme itself converts into a reactive species, which then inactivates that enzyme. The mechanism gives exceptional specificity.
Allosteric enzyme
A multi-subunit enzyme whose kinetics are sigmoidal rather than hyperbolic, so activity responds sharply to small changes in effector concentration.
Feedback inhibition
The end product of a pathway inhibits an early committed step, matching output to demand without altering enzyme amount.
Covalent modification
Reversible attachment of a group, most often a phosphate, that switches activity. It allows hormonal signals to be amplified through a kinase cascade.
Zymogen
An inactive precursor activated by selective proteolysis. Digestive proteases and clotting factors are stored this way so activation is fast and one-directional.
Coenzyme
A small organic cofactor that carries chemical groups or electrons between reactions. Many are derived from vitamins, which is why deficiencies hit specific pathways.