Enzyme Kinetics (Kieft L3,4) Flashcards
What is a co-factor (in an enzyme catalyzed rxn)?
Helper molecule that is not used up in the rxn.
E.g. metallic ions
What is a coenzyme?
Helps an enzyme by providing a molecule (e.g. methyl group) that is “used up” in the reaction.
What is a prosthetic group in an enzyme-catalyzed rxn?
A coenzyme or cofactor that is “tightly bound” to the enzyme.
What is a holoenzyme?
The combo of the enzyme and any prosthetic groups.
What is an apoenzyme or apoprotein?
protein / enzyme in isolation. not tightly bound as part of the holoenzyme.
What is the lock and key model for enzyme substrate binding?
The (now proven incorrect) theory that a substrate fits into an enzyme binding site like a key into a lock.
What is the induced fit model of enzyme substrate binding?
When the substrate binds to the enzyme there is a conformational change to get them “snug”.
How what does an enzyme do to move a rxn forward?
Lowers the activation energy to get to the transition state.
E + S ES EP E + P
activation energy to get to ES and then EP is lower than
S -> TS -> P
How does an enzyme affect the rate and equilibrium of a rxn?
increases the rate
does not change the equlib.
How do enzymes affect the standard enthalpy for a rxn?
Lowers standard enthalpy by stabilizing the transition state.
How does an enzyme affect the standard entropy for a rxn?
Increases standard entropy by decreasing entropic penalty.
e.g. increases the local/effective concentration of substrates by “putting them together”
How do enzymes use acid/base chemistry to help decrease activation energy?
Can donate or accept H+ ions from/to its own side chains.
e.g. -OH group on a serine, threonine or tyrosine
How do enzymes use covalent catalysis?
Transient covalent bonds with the substrate.
How do enzymes use metal ion catalysis?
ions help bind to substrate / shuffle around the charges
What is Km for an enzyme-catalyzed rxn?
the concentration of the substrate when the rxn is proceeding at half of its maximum possible rate.
