Sept 8 - Biochem 423 Robert A. Orlando, Ph.D. ENZYMES –...

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Unformatted text preview: Biochem 423 Robert A. Orlando, Ph.D. ENZYMES – MECHANISM OF ACTION ‐‐ THERMODYNAMICS LIFE OCCURS BY CONVERTING: SUBSTRATE (S) → PRODUCT (P) BUT ALSO ← SO, Keq = [P] [S] DIRECTION OF REACTION DEPENDS ON ∆G (FREE ENERGY CHANGE BETWEEN SUBSTRATE AND PRODUCT) FOR A SPONTANEOUS REACTION: X ∆G = − RT ln Keq [P] [S] ∆G R = GAS CONSTANT = 8.315 J/MOL•K T = ABSOLUTE TEMP = 298 K 43 | P a g e LOTS OF [P] AND LITTLE [S] = HUGE − ∆G = SPONTANEOUS Biochem 423 Robert A. Orlando, Ph.D. REMINDER…. ∆G IS ACTUALLY ∆G’˚ NOW, SPONTANEOUS REACTIONS NEED NO HELP TO PROCEED….BUT WHAT ABOUT MORE COMPLEX REACTIONS, SUCH AS DESCRIBED BY: WHERE ∆G˚ FOR CHEMISTS = STANDARD FREE‐ENERGY CHANGE (T = 298K; GAS PRESSURE = 1 ATM; EACH SOLUTE = 1M) (ABOVE CONDITIONS + PH = 7.0) AND ∆G’˚ = BIOCHEMICAL STANDARD FREE‐ENERGY CHANGE ∆Gactivation ENZYMES = REDUCE ∆Gactivation EQUILIBRIUM NOT AFFECTED ∆G’˚ = − RT ln Keq 44 | P a g e Biochem 423 Robert A. Orlando, Ph.D. ENZYMES provide multi‐step reactions: E + S ↔ ES ↔ EP ↔ E + P 45 | P a g e Biochem 423 Robert A. Orlando, Ph.D. BINDING ENERGY OF SUBSTRATE TO ENZYME REDUCES FREE‐ENERGY ∆GB = BINDING ENERGY CONTRIBUTED BY: H‐BONDING IONIC INTERACTIONS HYDROPHOBIC 46 | P a g e Biochem 423 Robert A. Orlando, Ph.D. REMEMBER…. ∆G’˚ IS A CONSTANT (= − RT ln Keq) BECAUSE OF STANDARDIZED CONDITIONS PH 7.0 298K 1 ATM PRESSURE BUT CONCENTRATION OF REACTANTS IS ALMOST NEVER 1.0 M IN BIOLOGY…. EACH REACTANT AT 1.0 M CONCENTRATION ACTUAL FREE ENERGY CHANGE (∆G) MUST REFLECT THE TRUE STARTING CONCENTRATIONS OF THE REACTANTS: ∆G = ∆G’˚ + RT ln [P] [S] ∆G IS POSITIVE IF [P]>>>[S] ∆G IS NEGATIVE DEPENDS ON [S]>>>[P] FOR EXAMPLE [P]/[S] = 10 ln(10) = +2.3 [P]/[S] = 0.01 ln (0.01) = −4.6 47 | P a g e Biochem 423 Robert A. Orlando, Ph.D. ONE FINAL NOTE…. ∆G ARE ADDITIVE TO DETERMINE ∆G FOR ENTIRE REACTION GLUCOSE + Pi → GLUCOSE‐6‐PHOSPHATE + H2O ∆G’˚ = 13.8 KJ/MOL (UNDER STANDARD BIOCHEMICAL CONDITIONS) ATP + H2O → ADP + Pi ∆G’˚ = −30.5 KJ/MOL SUM OF REACTIONS: GLUCOSE + ATP → ADP + GLUCOSE‐6‐PHOSPHATE ∆G’˚ = 13.8 KJ/MOL + −30.5 KJ/MOL = −16.7 KJ/MOL EXERGONIC REACTION 48 | P a g e ...
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This note was uploaded on 12/11/2010 for the course BIOC 423 taught by Professor Robert during the Fall '10 term at New Mexico.

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