Bioenergetics & Enzyme Kinetics Flashcards
2nd Law of Thermodynamics
The entropy of the universe is always increasing
Sources & Types of High Energy Bonds
Acetyl coA (thioester)
ATP (phosphoanhydride)
Phosphoenolpyruvate (PEP)
1st Law of Thermodynamics
The total energy of a system, including its surroundings, remains constant; energy is never created or destroyed but may be transferred or transformed
Relationship between free energy, enthalpy, and entropy of a system
dG = dH -TdS
Reduction Potential (E)
The more positive the value of E, the more a molecule likes to accepts electrons (become reduced); the more negative the value of E, the more a molecule likes to donate electrons (become oxidized)
As electrons pass from compounds with low (negative) to high (positive) E values, energy is released
Relationship between free energy and redox potential
dG = -nFdE
Enzyme cofactor
Small molecules (often metal ions) that function within an enzyme to catalyze a reaction; cofactors are not used up in the reaction
Coenzyme
Provide chemical groups for a catalyzed reaction and are used up by the reaction
Prosthetic Group
A coenzyme or cofactor that is tightly bound to the enzyme
Holoenzyme
The intact complex of an enzyme and it’s cofactor/coenzyme
Apoprotein
A protein enzyme in isolation, without it’s associated coenzyme/cofactor
Equation describing the speed of an enzymatic reaction
Velocity = k[S]
Km
Km is the substrate concentration at which Vo = 1/2Vmax
Km typically approximates intracellular concentrations of [S]
Kcat
measures the number of substrate molecules turned into product per enzyme molecule, per second
the larger the Kcat value, the faster the enzyme works to turnover
1/Kcat
the length of time required for the enzyme molecule to turn one molecule of substrate into product
Kcat/Km
A measure of comparing enzyme efficiency; the larger the value, the more efficient the enzyme
Catalytic Perfection
Kcat value approaching 10^8 - 10^9 - the enzyme is so efficient that the only limiting factor is the rate of diffusion
Competitive Inhibitors
Bind to the enzyme active site and block binding of the natural substrate
Kcat is unaffected, apparent increase in Km as [I] increases
Lineweaver Burke plot lines will intersect at the same y-intercept (at x=0) but have different slopes as [I] changes
Uncompetitive Inhibitors
Bind to the ES complex at a site other than the active site
Kcat, Vmax, and Km are affected; Lineweaver Burke plot lines run parallel
Mixed Inhibitors
May bind to either E or ES at a site other than the active site
Kcat, Vmax, and Km are changed; Lineweaver-Burke plot lines will intersect (X =/= 0) and have different slopes as [I] changes
