prentice hall c2002chapter 101 major pathways in cells metabolic fuels three major nutrients...
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Prentice Hall c2002 Chapter 10 1
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
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Prentice Hall c2002 Chapter 10 2
• Overview of catabolic pathways
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Prentice Hall c2002 Chapter 10 3
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, FADH2, QH2)
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Prentice Hall c2002 Chapter 10 4
Reducing Power
• Electrons of reduced coenzymes flow toward O2
• This produces a proton flow and a transmembrane potential
• Oxidative phosphorylation is the process by which the potential is coupled to the reaction: ADP + Pi ATP
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Prentice Hall c2002 Chapter 10 5
Compartmentation of metabolic processes
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Prentice Hall c2002 Chapter 10 6
Thermodynamics and Metabolism
• Free-energy change (G) is a measure of the chemical energy available from a reaction
G = Gproducts - Greactants
• H = change in enthalpy
• S = change in entropy
A. Free-Energy Change
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Prentice Hall c2002 Chapter 10 7
• Both entropy and enthalpy contribute to G
G = H - TS
(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
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Prentice Hall c2002 Chapter 10 8
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Prentice Hall c2002 Chapter 10 9
The Standard State (Go) Conditions
• Reaction free-energy depends upon conditions
• Standard state (Go) - defined reference conditions
Standard Temperature = 298K (25oC)
Standard Pressure = 1 atmosphere
Standard Solute Concentration = 1.0M
• Biological standard state = Go’ or G’o
Standard [H+] = 10-7 M (pH = 7.0) rather than 1.0M (pH = 1.0); [H2O]=55.5M; [Mg2+]=1mM
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Prentice Hall c2002 Chapter 10 10
B. Equilibrium Constants and Standard Free-Energy Change
• For the reaction: A + B C + D
Greaction = Go’reaction + RT ln([C][D]/[A][B])
• At equilibrium: Keq = [C][D]/[A][B] and Greaction = 0, so that:
Go’reaction = -RT ln Keq
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Prentice Hall c2002 Chapter 10 11
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]’
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Prentice Hall c2002 Chapter 10 12
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Prentice Hall c2002 Chapter 10 13
The Free Energy of ATP
• Energy from oxidation of metabolic fuels is largely recovered in the form of ATP
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Prentice Hall c2002 Chapter 10 14
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Prentice Hall c2002 Chapter 10 15
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Prentice Hall c2002 Chapter 10 16
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Prentice Hall c2002 Chapter 10 17
• Hydrolysis of ATP
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Prentice Hall c2002 Chapter 10 18
Complexes between ATP and Mg2+
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Prentice Hall c2002 Chapter 10 19
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