Biochem: chapter 6

1st order rxn

• rate depends on one reactant

• rate=k[A]^1

2nd order rxn

• Rate= k[A][B]

Zero Order rxn

k=[A]^1

• rate does NOT depend on concentration of reactants

• instead depends on catalyst/other factors

• occurs when reactant saturates enzyme

active site

substrate gets bound noncovalent forces

E+S=

enzyme substrate complex

Lock and Key model

• similar shape of the substrate

• model doesn’t take into account conformational flexibility of protein

Induced fit model

• binding induces a conformational change in the enzyme

• shape of the protein is different before and after substrate is bound

• most probable

• lower activation energy

• transition state

• important to not be too tightly bound so substrate can release easier

Michaels Menten Equation

• K1= rate constant foward rxn to ES complex

• K-1= rate constant for reverse back to substrate

• k2= rate constant to product, not reversible

• v=

• (Vmax[S])/(Km+[S])

Km

substrate conc at which rxn proceeds at ½ the max velocity

½ active sites are occupied

substrates affinity to enzyme

lower Km value= higher affinity of substrate to enzyme

Vmax

when enzyme is saturated with substrate

units are in per second s^-1 only when rxn is in zero order

non allosteric enzyme

• hyperbolic graph

lineweaver burk plot

Competitive inhibitor

• reversible

• blocks substrate from binding

• Vmax Unchanged: this is the max amount of substrate enzyme can react with

• Km increases: amount of S needed to reach ½ maximum V increases dur to inhibitor

• can be overcome by adding high conc of substrate

Non competitive inhibitors

• irreversible

• binds to a different site on the enzyme, substrate can still bind but cannot catalyze the reaction

• Km: stays the same: substrate can bind, x intercept doesnt change

• Vmax: decreases: vmax is at turnover (equal to catalytic constant)

uncompetitive inhibition

• inhibitor can bind to ES complex, but not to free E

• Vmax and Km decrease

• Km decreases because it makes more enzyme substrate to compensate to increase binding affinity

Mixed inhibitors

• binding of inhibitor affects the binding of substrate and vice cersa

• Km increases: doesn’t allow substrate to bind

• Vmax: decreases, can produce product

• lines cross at left hang quadrant