10: Enzymes Flashcards
what is a catalyst?
a substance that increases the rate of a chemical reaction w/o changing itself
what is an enzyme?
a protein that acts as a biological catalyst
what are the different modes of enzyme binding?
lock and key - the enzyme and substrate fit together
conformation selection - the conformation of the enzyme varies, ONE conformation recognizes the substrate (ligand)
induced fit - binding the substrate induces a change in the enzyme
what are the different classes of enzymes?
EC 1 - oxidoreductases
EC 2 - transferases
EC 3 - hydrolases
EC 4 - lysases
EC 5 - isomerases
EC 6 - ligases
what are the two important coenzymes?
NAD+/NADH
- NADH is a reducing agent (source of electrons)
coenzyme A/Acetyl CoA
- acetyl CoA is the source of carbon atoms
what is activation energy?
activation energy is the amount of energy needed to overcome the transition state barrier (energy needed to turn reactants to products)
how would a catalyst affect a reaction?
enzymes are going to lower activation energy, but do not change the free energy.
- it will take less energy to produce products
- some enzymes stabilize intermediate state of the reactant
how can ATP be used alongside enzymes?
ATP coupling
- enzymes can use ATP to drive thermodynamically unfavorable reactions
explain E+S <-> ES <-> E+P
when the enzyme complexes with the substrate, it either dissociates into unchanged substrate or it proceeds irreversibly forward to product
K1 (formation) = E+S –> ES
K-1 (dissociation) = ES –> E+S
K2 (progress towards product) = ES –> E+P
how does the michaelis-menton graph show enzymatic reaction?
As substrate concentration increases, the reaction reaches a maximum velocity, Vmax
- Km is the substrate concentration that produces Vmax/2
what are the types of enzyme inhibition?
- competitive
- noncompetitive
- uncompetitive
- irreversible
competitive inhibitor: binding site? kinetic effect?
binding site: catalytic site
kinetic effect: Vmax is unchanged, Km is increased
noncompetitive inhibitor: binding site? kinetic effect?
binding site: E or ES complex
kinetic effect: Km appears unaltered, Vmax is decreased
uncompetitive inhibitor: binding site? kinetic effect?
binding site: ES complex
kinetic effect: apparent Vmax decreased, Km is decreased
how does is binding affinity associated with Kd/Ki value?
the lower the Kd or Ki value, the stronger the affinity
- Ki can be viewed as a type of dissociation constant
