Enzyme Kinetics LO Flashcards
what is an enzyme?
biological catalyst that increases rate of reaction without being changed in process
what do enzymes do to the activation energy?
decrease it
what are 2 ways enzymes lower activation energy?
- bind during transition state
2. rearrangement of specific active site chemistry
how does enzyme lower activation energy when bound during transition state?
enzyme binds to molecule that is in transition state, keeps molecule in transition state until ready to react with other reactant
what is meant by covalent chemistry in regards to enzymes?
enzyme creates covalent bond with substrate to help catalyze reaction
what is an example of metal ion chemistry in regards to enzymes?
alcohol dehydrogenase has a Zn+2 ion within active site.
- interacts with alcohol using reduction of NAD+ to NADH
how does acid/base chemistry work within an enzyme?
enzyme can extract or donate protons to speed up reaction
what is a cofactor in an enzymatic reaction?
metallic ions in the active site that assist in biochemical transformations
what is a co-enzyme in an enzymatic reaction?
small organic molecules that transport chemical groups from one enzyme to another
what is Km?
substrate concentration at which the velocity of the reaction is equal to 1/2 of the Vmax
when does the concentration of the substrate equal Km?
when V0 = 1/2 Vmax
what is Kcat?
general rate constant that describes the overall rate of the reaction (turnover number)
what terms describe the overall efficiency of an enzyme?
Km and Kcat
what does a higher Km indicate in regards to the amount of substrate needed to reach 1/2 Vmax?
need more substrate
what does a higher Kcat indicate in relation to the speed of the reaction?
faster reaction with higher Kcat
what is Kcat equal to?
number of substrate molecules converted to product in given unit of time using single molecule of enzyme when enzyme is saturated with substrate
how do you calculate Km from a graph of velocity vs [S]?
locate point on y-axis that looks like 1/2 Vmax, trace across to point on curve, trace down vertically to X-intercept this is Km
between cofactors and coenzymes, which chemical groups are “used up”?
coenzymes
what is a prosthetic group?
coenzyme or cofactor that is tightly bound to an enzyme
what is a haloenzyme?
enzyme with prosthetic group
what is a protein in isolation without a prosthetic group?
apoenzyme or apoprotein
what are the 4 types of inhibitors?
- competitive inhibitors
- non-competitive inhibitors
- reversible inhibitors
- irreversible inhibitors
what is a competitive inhibitor?
binds to the active site and prevents binding of substrate
what do competitive inhibitors do the the Km and the Vmax?
changes Km but not Vmax
what does Ritonavir inhibit?
HIV protease, competitive
what is methotrexate used in the treatment of?
cancer, competitive
what is a non-competitive inhibitor?
binds to allosteric site and prevents binding of substrate
what do non-competitive inhibitors do to the Km and Vmax?
changes both Kcat and Vmax but Km remains unchanged
what type of inhibitor is lithium and what is it used in the treatment of?
non-competitive, bipolar disorder
what is a reversible inhibitor?
binds to enzymes through non-covalent interactions but can be reversed
what is a irreversible inhibitor?
covalently modifies enzyme and “kills the enzyme for good”
what type of inhibitor is penicillin?
irreversible inhibitor
what is the mechanism of penicillin?
binds to DD-transpeptidase which makes cross-links in peptidoglycan molecules in bacteria, bacteria can’t make cell walls and then die
what type of inhibitor is DIFP?
irreversible inhibitor
what is the mechanism of DIFP?
cleaves serine 195 in chymotrypsin, chymotrypsin then can never covalently bind with its substrates
what is an example of covalent modification to activate an enzyme?
phosphorylation can activate or deactivate
what binds to trypsin to deactivate it?
BPTI
how is trypsinogen activated?
proteolytic cleavage by enteropeptidase turns trypsinogen into trypsin
what does uncompetitive inhibition do to Kcat, Vmax and Km?
changes all of them
