Enzyme Kinetics

Each list begins with basic conceptual vocabulary you need to know for MCAT questions and proceeds to advanced terms that might appear in context in MCAT passages. The terms are links to Wikipedia articles.
Enzyme inhibitor
An enzyme inhibitor is a molecule that binds to an enzyme and decreases its activity.
Enzyme activators
Enzyme activators are molecules that bind to enzymes and increase their activity.
Enzyme assays
Enzyme assays are laboratory methods for measuring enzymatic activity.
Michaelis constant
The value of the Michaelis constant KM is numerically equal to the substrate concentration at which the reaction rate is half of Vmax.
Competitive inhibition
Competitive inhibition is interruption of a chemical pathway owing to one chemical substance inhibiting the effect of another by competing with it for binding or bonding.
Non-competitive inhibition
Non-competitive inhibition is a type of enzyme inhibition where the inhibitor reduces the activity of the enzyme and binds equally well to the enzyme whether or not it has already bound the substrate.
Allosteric regulation
Allosteric regulation is the regulation of an enzyme by binding an effector molecule at a site other than the enzyme's active site.
Steady state
A steady state is a situation in which all state variables are constant in spite of ongoing processes that strive to change them.
Lineweaver–Burk plot
A method for analysis of the Michaelis–Menten equation, the Lineweaver–Burk plot (or double reciprocal plot) provides a useful graphical representation of kinetics data.
Uncompetitive inhibition
Uncompetitive inhibition, also known as anti-competitive inhibition, takes place when an enzyme inhibitor binds only to the complex formed between the enzyme and the substrate (the E-S complex).
Mixed inhibition
Mixed inhibition is a type of enzyme inhibition in which the inhibitor may bind to the enzyme whether or not the enzyme has already bound the substrate but has a greater affinity for one state or the other.
Turnover number
Turnover number (also termed kcat) is defined as the maximum number of chemical conversions of substrate molecules per second that a single active site will execute for a given enzyme concentration.
Specificity constant
The specificity constant (also called catalytic efficiency, kcat/Km, is a measure of how efficiently an enzyme converts substrates into products.
Cooperative binding
Cooperative binding occurs in binding systems containing more than one type, or species, of molecule and in which one of the partners is not mono-valent and can bind more than one molecule of the other species.
Effector molecule
A effector molecule is usually a small molecule that selectively binds to a protein and regulates its biological activity.
Dissociation constant
A dissociation constant (Kd) is a specific type of equilibrium constant that measures the propensity of a larger object to separate (dissociate) reversibly into smaller components, as when a complex falls apart into its component molecules, or when a salt splits up into its component ions.
Binding constant
The binding constant, or association constant, is a special case of the equilibrium constant K, and is the inverse of the dissociation constant.
Suicide inhibition
Suicide inhibition is an irreversible form of enzyme inhibition that occurs when an enzyme binds a substrate analog and forms an irreversible complex with it through a covalent bond during the normal catalysis reaction.
Sigmoid function
A sigmoid function is a mathematical function having a characteristic S-shaped curve.
Monod-Wyman-Changeux model
The Monod-Wyman-Changeux model (MWC model) describes allosteric transitions of proteins made up of identical subunits.
Diffusion-limited enzyme
A diffusion-limited enzyme catalyses a reaction so efficiently that the rate limiting step is that of substrate diffusion into the active site, or product diffusion out. This is also known as kinetic perfection or catalytic perfection.
Hill coefficient
In cooperative binding, the Hill coefficient provides a way to quantify the degree of interaction between ligand binding sites.
Cooperativity is a phenomenon displayed by systems involving identical or near-identical elements, which act dependently of each other, relative to a hypothetical standard non-interacting system in which the individual elements are acting independently.
Sequential model
The sequential model (also known as the KNF model) is a theory that describes cooperativity of protein subunits. It postulates that a protein's conformation changes with each binding of a ligand, thus sequentially changing its affinity for the ligand at neighboring binding sites.
Allosteric modulators
Allosteric modulators are a group of substances that bind to a receptor to change that receptor's response to stimulus.
Enzyme unit
The enzyme unit (symbol U, sometimes also IU) is a unit for the catalytic activity of an enzyme.
The katal is the unit of catalytic activity in the International System of Units (SI).
Morpheeins are proteins that can form two or more different homo-oligomers, but must come apart and change shape to convert between forms.
Secondary plot
A secondary plot uses the intercept or slope from several Lineweaver–Burk plots to find additional kinetic constants.

The Integrated MCAT Course is a trademark of Wisebridge Learning Systems. Unless otherwise specified, the works of the Integrated Course are published under a Creative Commons Attribution NonCommercial ShareAlike License. MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the Integrated MCAT Course. The Integrated MCAT Course offers our customers no guarantees regarding eventual performance on the MCAT.