Prentice Hall c2002Chapter 101 Major Pathways in Cells Metabolic fuels Three major nutrients consumed by mammals: (1) Carbohydrates - provide energy (2) Proteins - provide amino acids for protein synthesis and some energy (3) Fats - triacylglycerols provide energy and also lipids for membrane synthesis

Prentice Hall c2002Chapter 102 Overview of catabolic pathways

Prentice Hall c2002Chapter 103 Catabolism produces compounds for energy utilization Three types of compounds are produced that mediate the release of energy (1) Acetyl CoA (2) Nucleoside triphosphates (e.g. ATP) (3) Reduced coenzymes (NADH, FADH 2, QH 2 )

Prentice Hall c2002Chapter 104 Reducing Power Electrons of reduced coenzymes flow toward O 2 This produces a proton flow and a transmembrane potential Oxidative phosphorylation is the process by which the potential is coupled to the reaction: ADP + P i ATP

Prentice Hall c2002Chapter 105 Compartmentation of metabolic processes

Prentice Hall c2002Chapter 106 Thermodynamics and Metabolism Free-energy change (  G) is a measure of the chemical energy available from a reaction  G = G products - G reactants  H = change in enthalpy  S = change in entropy A. Free-Energy Change

Prentice Hall c2002Chapter 107 Both entropy and enthalpy contribute to  G  G =  H - T  S (T = degrees Kelvin) -  G = a spontaneous reaction in the direction written +  G = the reaction is not spontaneous  G = 0 the reaction is at equilibrium Relationship between energy and entropy

Prentice Hall c2002Chapter 108

Prentice Hall c2002Chapter 109 The Standard State (  G o ) Conditions Reaction free-energy depends upon conditions Standard state (  G o ) - defined reference conditions Standard Temperature = 298K (25 o C) Standard Pressure = 1 atmosphere Standard Solute Concentration = 1.0M Biological standard state =  G o’ or  G ’o Standard [H + ] = M (pH = 7.0) rather than 1.0M (pH = 1.0); [H 2 O]=55.5M; [Mg 2+ ]=1mM

Prentice Hall c2002Chapter 1010 B. Equilibrium Constants and Standard Free-Energy Change For the reaction: A + BC + D  G reaction =  G o’ reaction + RT ln([C][D]/[A][B]) At equilibrium: Keq = [C][D]/[A][B] and  G reaction = 0, so that:  G o’ reaction = -RT ln K eq

Prentice Hall c2002Chapter 1011 C. Actual Free-Energy Change Determines Spontaneity of Cellular Reactions When a reaction is not at equilibrium, the actual free energy change (  G) depends upon the ratio of products to substrates Q = the mass action ratio  G =  G’ o + RT ln Q Where Q = [C]’[D]’ / [A]’[B]’

Prentice Hall c2002Chapter 1012

Prentice Hall c2002Chapter 1013 The Free Energy of ATP Energy from oxidation of metabolic fuels is largely recovered in the form of ATP

Prentice Hall c2002Chapter 1014

Prentice Hall c2002Chapter 1015

Prentice Hall c2002Chapter 1016

Prentice Hall c2002Chapter 1017 Hydrolysis of ATP

Prentice Hall c2002Chapter 1018 Complexes between ATP and Mg 2+

Prentice Hall c2002Chapter 1019 ATP is an “energy-rich” compound A large amount of energy is released in the hydrolysis of the phosphoanhydride bonds of ATP (and UTP, GTP, CTP) All nucleoside phosphates have nearly equal standard free energies of hydrolysis