Lecture 3 August 5, 2005 Lehninger (4 th Edition), Chapter 13

METABOLIC PATHWAYS

Types of Organic Reactions 1) Group transfer Glucose + ATP Glu-6-P + ADP H 2 O + ATP P i + ADP 2) Oxidation-reduction reactions Ethanol + NAD + acetaldehyde + NADH + H + 3) Eliminations, isomerizations, rearrangements aldose ketose 4) reactions involving making or breaking of C-C bonds Fru-1,6, bisphosphate dihydroxyacetone-phosphate + glyceraldehyde-3phosphate

Biochemical reactions are subject to the laws of thermodynamics

A + B C + D  G = 0 at equilibrium

Gas constant R = J/mol. K = cal/mol. K 1 cal = J at 25 o C RT = kJ/mol = kcal/mol

Many reactions in biological systems are by themselves not energetically favored (  G > 0) they have to be “pushed” 1. By changing concentrations of reactants 2. By coupling them to energy releasing reactions 3. enzymatic mechanisms are designed to accomplish this

HIGH ENERGY PHOSPHATE COMPOUNDS ATP

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_ _ _ _ _

a mixed anhydride

LNC 14-8

Oxidation - Reduction Reactions a second major source of chemical free energy for biological work

LNC 14.14

[lactate] [NAD+]  G =  G o ’ + RT ln [pyruvate] [NADH] [lactate] [NAD+]  E =  E o ’ - RT/n F ln [pyruvate] [NADH]  G = - n F  E

transfer of hydride ion (two electrons) in one step LNC 14-15a

LNC 14-15b

FAD FMN LNC two steps one electron and one proton transferred in each step

METABOLIC PATHWAYS

End of lecture 3 August 5, 2005