Basic Concepts of Enzyme Action Flashcards
What do enzymes do?
Accelerate the rate of rxns, highly specific in both the rxns they catalyze and choice of reactants (substrate)
What are proteolytic enzymes?
Catalyze proteolysis, which is hydrolysis of a peptide bond (breakage of bond with H2O), differ greatly in degrees of substrate specificity
What are the six major classes of enzymes?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
Oxidoreductases
Catalyze redox rxns (transfer e- between molecules)
Transferases
Transfer functional groups between molecules
Hydrolases
Cleaves molecules by addition of H2O
Lyases
Adds atoms or functional groups to a double bond or removes them to form a double bond
Isomerases
Move functional groups within a molecule
Ligases
Join 2 molecules in rxn powered by ATP hydrolysis
Enzymes often cannot meet the chemical needs required for catalysis to take place, so they depend on
the presence of cofactors (small molecules)
- Enzyme without cofactor = apoenzyme
- Enzyme with cofactor = holoenzyme
Cofactors are divided into 2 groups:
- Coenzymes
2. Metals
Coenzymes
Small organic molecules derived from vitamins, similar to cosubstrates bc they bind to the enzyme and are released from it, used by variety of enzymes
Metals
Bound at the active site and participate in the rxn
Free Energy Change
For spon, deltaG = (-)
At equil, deltaG = 0
deltaG is independent of pathwaymechanism of transformation
deltaG tells NOTHING about rate of rxn
For a rxn to be energetically favourable (spon), deltaG must be
negative
Spon rxns are NOT instantaneous
Enzymes make a spon rxn kinetically favourable
How do enzymes accelerate rxns?
By decreasing the activation energy to overcome the activation energy barrier
Enzymes lower the activation energy by stabilizing the transition state
What are the features of enzyme active sites?
- Residues forming the active site come from different positions in the primary sequence
- Small volume of total protein
- Unique microenvironment (polar residues on inside when normally outside)
- Forms many weak interactions with substrates
- Specificity of substrate binding depends on the precise arrangement of atoms in the active site
What is binding energy?
The free energy that is released when many weak interactions form between the enzyme and substrate and transition state
- Only the correct substrate can maximize the amount of binding energy = specificity
When does maximal binding energy occur?
During the formation of the transition state
