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Properties of Enzymes
A catalyst enhances the rate of reaction by decreasing the activation energy for a reaction
catalyze redox reactions
transfer a group from one molecule to another
cleave bonds by adding water
catalyze removal of groups to form double bonds or the reverse
catalyze intramolecular rearrangements
bond two molecules together
Chymotrypsin. At low substrate concentrations, the reaction is ___ order in substrate. As the concentration of substrate increases, the order changes and approaches ___. Thus the graph is ___.
Aspartate transcarbamoylase (ATCase) leads to the synthesis of ___.
The plots for cymotrypsin and aspartate transcarbamoylase should remind us of the oxygen bindingcurves for myoglobin and hemoglobin respectively. Thus, cymotrypsin is ___ and ATCase is an ___ enzyme.
Michaelis-Menten Kinetics explains the behavior of ___ enzymes. It assumes an ___ complex is formed.
At low substrate concentrations, the reaction is ___ order with respect to substrate.
non-allosteric: At high substrate concentrations, the enzyme is saturated with substrate. The order is ___ and a ___
The lower the Km, the ___ the affinity for complex formation.
kcat = Vmax/[Et]
km = [S] at the ___ point
- y = 1/v
- m = Km / Vmax
- x = 1/S
- b = 1/Vmax
competitive inhibitor looks structurally like the ___and binds to the enzyme at the ___.
An uncompetitive inhibitor binds to the ___ complex.
- or other than active site
For competitive inhibitor, Vmax ___, slope ___ and Km ___.
Noncompetitive Inhibitor, Vmax ___ slope ___ and Km ___.
Proximity and Strain Effects
Substrate closely approaches the catalytic site with proper orientation
A hydrophobic pocket in the enzyme lowers the surrounding dielectric constant allowing electrostatic interaction between E and S.
Enzyme side chains act as proton donors and acceptors
A nucleophilic side chain forms an unstable covalent bond to the substrate.
Transition metals are useful because they
- Have a high positive charge density.
- Act as Lewis acids (accepte pairs). Or neucleophile
- Can mediate redox reactions
- Help polarize water molecules
Nicotinic acid (niacin) is involved in ___ reactions.
The active site on Chymotrypsin (CT) involves the ___.
- serine 195 residue
- histidine 57 residue
for Chymotrypsin, The histidine acts as a ___ catalyst, converting the serine to its ___ and making it a better ___ for attack at the carbonyl carbon to be hydroylzed.
- general base
methods that organisms use to regulate enzyme activity are:
- Genetic control
- Covalent modification
- Allosteric regulation
Genetic control -->
- enzyme induction
- e.coli uses lactose in the absence of glucose
- phosphorylation and dephosphorylation
- Glycogen phosphorylation, methylation and acetylation
inactive enzyme precursor that requires a biochemical change to become an active enzyme
Pacemaker (regulatory) enzymes usually catalyze the “committed” step in a series of biochemical reactions or a step where branching to two paths can occur.
Eukaryotic cells are divided into organelles which often allows for separation of opposing processes