Bishop Chapter 13 Enzymes Flashcards
Define active site.
A region on an enzyme that binds to a protein or other substance during a reaction.
Define substrate.
The substance on which an enzyme acts.
Define allosteric site.
A site that allows molecules to either activate or inhibit (or turn off) enzyme activity.
Define isoenzyme.
A group of enzymes that catalyze the same reaction but have different enzyme forms and catalytic efficiencies.
Isozymes are usually distinguished by their electrophoretic mobilities.
Define isoform.
When an enzyme is subject to posttranslational modifications.
Define cofactor.
A non-protein chemical compound or metallic ion that is required for an enzyme’s role as a catalyst.
Define activators.
Inorganic cofactors, such as chloride or magnesium ions.
Define coenzyme.
An organic cofactor, such as nicotinamide adenine dinucleotide (NAD).
Define zymogen.
Enzymes that are secreted from an organ of production in a structurally inactive form.
Define oxidoreductases.
Catalyze an oxidation-reduction reaction between two substrates.
Define transferases.
Catalyze the transfer of a group other than hydrogen from one substrate to another.
Define hydrolases.
Catalyze hydrolysis of various bonds.
Define lyases.
Catalyze removal of groups from substrates without hydrolysis; the product contains double bonds.
Define isomerases.
Catalyze the interconversion of geometric, optical, or positional isomers.
Define ligases.
Catalyze the joining of two substrate molecules, coupled with breaking of the pyrophosphate bond in ATP or a similar compound.
Define activation energy.
The energy required to raise all molecules in 1 mole of a compound at a certain temperature to the transition state at the peak of the energy barrier.
What is a way to provide more energy for a reaction?
Increase temperature.
Define absolute specificity.
The enzyme combines with only one substrate and catalyzes only the one corresponding reaction.
Define group specific.
Enzymes that combine with all substrates containing a particular chemical group (i.e. phosphate ester).
Define bond specificity.
Enzymes that are specific to chemical bonds.
Define stereoisomeric specificity.
Enzymes that predominantly combine with only one optical isomer of a certain compound.
What is a major influence at which an enzymatic reaction proceeds, whether forward or reverse?
Substrate concentration.
Define first-order kinetics.
When the reaction rate is directly proportional to substrate concentration.
Define zero-order kinetics.
When the reaction rate only depends on enzyme concentration.
Define the Michaelis-Menten constant (Km).
A constant for a specific enzyme and substrate under defined reaction conditions and is an expression of the relationship between the velocity of the enzymatic reaction and substrate concentration.
The higher the ___ level, the faster the reaction will proceed.
enzyme
How would changing the pH of a solution effect the enzymes?
May denature an enzyme or influence its ionic state.
How does low temperatures affect enzymes?
Renders them reversibly inactive; freezing prevents activity loss until analysis.
Define competitive inhibitors.
Inhibitors that physically bind to the active site of an enzyme and compete with the substrate for the active site.
Define noncompetitive inhibitors.
Inhibitors that bind an enzyme at a place other than the active site and may be reversible.
Define uncompetitive inhibition.
The inhibitor binds to the ES complex - increasing substrate concentration results in more ES complexes to which the inhibitor binds and, thereby, increases the inhibition.
During uncompetitive inhibition, how would the reaction be affected if you increased substrate concentration?
Increases inhibition.
What is the common method for enzyme quantitation?
Measurement of catalytic activity; activity is related to concentration.
What kind of precautions should you take when doing enzyme quantitation in zero-order kinetics?
Ensure the absence of inhibitors, and other variables that may influence the rate of the reaction are controlled.
For measurement of enzymatic reactions, describe the methodology of the fixed-time method.
The reactants are combined, the reaction proceeds for a designate time, the reaction is stopped (usually by inactivating the enzyme with a weak acid), and a measurement is made of the amount of reaction that has occurred.
For measurement of enzymatic reactions, describe the methodology of the continuous-monitoring (or kinetic assays).
Multiple measurements, usually of absorbance change, are made during the reaction, either at specific time intervals or continuously by a continuous-recording spectrophotometer.
