Enzyme Kinetics & Inhibition Flashcards
enzyme
catalysts that speed up the rate of reaction by lowering the activation energy without being changed themselves; virtually all enzymes are proteins although some catalytically active RNAs exist
Gibbs free energy of activation
the difference in free energy between the substrate and transition state that must be overcome for the reaction to proceed; the transition state has the highest free energy in the pathway
Free energy change (delta G)
difference in energy level between the product and substrate
- negative = spontaneous
- positive = unfavorable and non-spontaneous
substrate binds the active site of the enzyme by what kinds of forces?
- multiple weak forces such as electrostatic interactions, H-bonds, van der Waals, and hydrophobic ineractions
- in some cases also reversible covalent bonds
oxidoreductases
transfer electrons
-ex: dehydrogenases
transferases
transfer of a functional group from one molecule to another
-ex: hexokinase
hydrolases
break bonds by adding water
-ex: trypsin
lyases
cleave bonds without the addition of water
-ex: pyruvate decarboxylase
isomerases
transfer of groups within a molecule
-ex: maleate isomerase
ligases
responsible for joining two large biomolecules (often of the same type)…bond formation coupled to ATP hydrolysis
-ex: pyruvate carboxylase
synthase vs. synthetases
synthetases require high energy phosphates (such as ATP or GTP) to catalyze bond formation, whereas synthases do not
isoenzymes
different forms of an enzyme which catalyze the same reaction, but which exhibit different physical or kinetic properties
the shape of the resulting graph when V0 is plotted against [S]
hyperbolic curve
cooperative enzymes show what kind of curve?
sigmoidal
irreversible inhibitors
bind tightly, often covalently, and permanently inactivate the enzyme
