Enzymes Flashcards
Enzyme terminology
An enzymes name often describes its function. For example. glucokinase is an enzyme that catalyzes the phosphorylation of glucose using a molecule of ATP.
Kinase
Catalyzes transfer of a phosphate group from a high-energy moelcule (usually ATP) to a substrate (ie phosphofructokinase)
Phosphorylase
Adds inorganic phosphate onto substrate without using ATP (ie glycogen phosphorylase)
Phosphatase
Removes phosphate group from substrate (ie., fructose 1,6 bisphosphatase 1)
Dehydrogenase
Catalyzes oxidation-reduction reaction (ie., pyruvate dehydrogenase)
Hydroxylase
Adds hydroxyl group (-OH) onto substrate (ie., tyrosine hydroxylase)
Carboxylase
Transfers CO2 groups with the help of biotin (ie., pyruvate carboxylase)
Mutase
Relocates a functional group within a molecule (ie., vitamin B12 dependent methylmalonyl-CoA
During an enzyme catalyzed reaction, the substrate most likely binds to which of the following?
Active site
By which of the following mechanisms do enzymes catalyze chemical reactions?
Lowering activation energy of the reaction
Pyruvate + NADH+ H+ → Lactate + NAD + . The role of NAD+ in this reaction is
Coenzyme – cosubstrate
Km refers to which of the following?
The affinity of the enzyme for its substrate
What is the effect of non-competitive inhibitor on Vmax & Km of an enzyme catalyzed reaction?
Vmax is lowered while Km remains unchanged
In non- competitive inhibition, the inhibitor binds to a site different from the active site of the enzyme. Since the inhibitor does not interfere with the binding of substrate to enzyme, there is no change in the affinity of the enzyme for its substrate (Km remains unchanged). However, the presence of inhibitor on the enzyme will affect its catalytic activity thereby decreasing the Vmax. Unlike competitive inhibition, increasing substrate concentration would have no effect on Vmax. Also refer to the image attached below to see the changes in enzyme kinetics for non- competitive inhibition.
The plot (in red) in the given image represents the action of ATP on the enzyme Phosphofructokinase(PFK) -1. (Plot in blue represents the enzyme kinetics of PFK -1 in the absence of ATP) What is the effect of ATP on the enzyme?
Acts as a negative effector
What can change Km
Ph
Temperature
Cofactor
Inhibitors
Decrease in Km requires less substrate concentration to reach _____
1/2 max velocity
