PINAUD EXAM 2 Flashcards
basic characteristics of enzymes
increase rate by lowering AE
do not alter equilibrium constant
often require co-factors
usually proteins, sometimes RNA
highly specific to substrate and reaction
protease
catalyzes the hydrolysis of protein peptide bonds
thrombin
proteolytic enzyme in blood clotting
Cuts between Arg and Gly
trypsin
enzyme in the digestive system
cuts after Arg or Lys
holoenzyme
apoenzyme (inactive) + cofactor (coenzyme or metal)
∆G equation
∆G = ∆G° + RT ln [products]/[reactants]
Keq equation
kf/kr
3 ways to increase the rxn rate (k)
increase substrate conc.
increase T
decrease activation energy
ES complex characteristics
shape of active catalytic pocket is 3D (via steric hindrances of AA residues) and flexible, often nonpolar
induced fit: change conformation after binding
multiple weak interactions between E and S (H bonding, electrostatic, hydrophobic, VDWs)
transition state
short lived chemical state
highest peak of ∆G diagram
strong binding and flexibility of ES complex promotes formation of transition state
kinetic evidence for ES complex
rxn rate increases with increases substrate conc until a plateau (enzyme conc)
physical evidence for ES complex
x-ray crystallography
binding energy
some free energy released upon binding ES, helps form active site and lowers ∆G of transition state
enzymes speed up biochemical rxns by…
specific substrate recognition
multiple reactive steps at catalytic site
strong binding to transition state
efficient release of product
first order rxn
V = k[S], units s-1
second order rxn
V = k[S][B], units M-1 s-1
at low [S]…
Vo proportional to [S]
at high [S]…
Vo independent of [S]
Km
substrate concentration at 1/2(Vmax)
kcat
turnover rate (molecules/s), only works when Vmax has been reached
Michaelis-Menten equation
Vo = Vmax ([S]/[S] + Km)
what does Km say about the strength of ES complex?
low Km = stronger binding
high Km = weaker binding
enzyme efficiency measurement
kcat/Km
10^8 to 10^9 is catalytically perfect
lineweaver burke plot
reciprocal of Michaelis-Menten curve, linear
1/Vo = (Km/Vmax)(1/[S]) + 1/Vmax