F212 1.3 - Enzymes Flashcards
Activation energy
The amount of energy needed to go from either substrate or product to the transition state i.e. the level of energy needed for the reaction to take place and which is reduced by an enzyme
Active site
The region of the enzyme to which the substrate binds due to complementary shape and charge distributions
Allosteric activator
A substance binding to an allosteric site and activating the enzyme
Allosteric inhibitor
A substance binding to an allosteric site and inhibiting the enzyme
Allosteric site
A site spatially distinct from the active site to which a molecule binds influencing the shape of the enzyme, including the active site
Catalyst
Something which changes the rate of a reaction (usually speeds it up) but is itself unchanged at the end of the reaction
Coenzyme
An organic non-protein molecule that binds to the enzyme at the same time as the substrate and is essential for catalysis to proceed during the course of which the coenzyme is modified and released in a different form. Important coenzymes are NAD, NADP and FAD
Cofactor
A molecule or ion which helps an enzyme to work. It can be a coenzyme or an inorganic ion
Competitive inhibitor
A substance able to reduce the rate of an enzyme-catalysed reaction by binding at the active site usually because of a close structural and charge distribution to those of the normal substrate
End-product inhibition
The end-product of a metabolic pathway acting to inhibit the pathway, usually by reversibly inhibiting one of the enzymes at the beginning of the pathway. An example of negative feedback
Enzyme
A protein that acts as a biological catalyst by lowering the activation energy needed to achieve the transition state.
Enzyme-substrate complex:
The intermediate structure formed by substrate binding to enzyme that develops into the transition state which then becomes the enzyme product complex
Extracellular enzyme
An enzyme made in the cell then secreted to act outside of the cell
Induced fit hypothesis
A modern theory relating to enzyme catalysis which suggests that both enzyme and substrate (or either) undergoes a conformational change on forming the enzyme-substrate complex improving the complementary fit between them and making catalysis more probable
Intracellular enzyme
An enzyme which acts inside the cell
Irreversible inhibitor
An inhibitor which attaches permanently to an enzyme
Optimum
The best or most favourable condition. Each enzyme has an optimum pH
Lock-and-key hypothesis
An old theory relating to enzyme catalysis which drew an analogy between the enzyme and a lock and its substrate as the only key that would fit thereby explaining the specific nature of enzyme catalysis
Maximum velocity
The greatest rate of catalysis possible by an enzyme achieved only when the substrate concentration is high enough to keep the active site reloaded with a fresh molecule as fast as product is released
Non-competitive inhibitor
A substance able to reduce the rate of an enzyme-catalysed reaction by binding to a site other than the active site and interfering with the catalytic mechanism
Product
The substance made in an enzyme-catalysed reaction from the substrate and released from the active site
Reversible inhibitor
An inhibitor which attaches temporarily to an enzyme
Substrate
The substance used up in an enzyme-catalysed reaction and converted to product after binding to the active site
Transition state
A very high energy, very unstable molecular structure in between substrate and product found only very briefly and only in the active site as the two interconvert
