An Overview of Metabolism and Biochemical Energy Stage 3 Citric acid cycle Acetyl groups are oxidized inside cellular mitochondria to yield CO2 This stage releases a large amount of energy Stage 4 The electron transport chain Energy made in the citric acid cycle used during the fourth stage,the electron-transport chain,to accomplish the endergonic phosphorylation of ADP with hydrogen phosphate ion(HOPO32-,abbreviated Pi)to give ATP
Stage 3 Citric acid cycle ▪ Acetyl groups are oxidized inside cellular mitochondria to yield CO2 ▪ This stage releases a large amount of energy Stage 4 The electron transport chain ▪ Energy made in the citric acid cycle used during the fourth stage, the electron-transport chain, to accomplish the endergonic phosphorylation of ADP with hydrogen phosphate ion (HOPO3 2- , abbreviated Pi) to give ATP An Overview of Metabolism and Biochemical Energy
An Overview of Metabolism and Biochemical Energy ATP,the final result of food catabolism,has been called the 'energy currency"of the cell Energy production and use in living organisms revolve around the ATPs ADP interconversion Catabolic reactions "buy"ATP with energy released by synthesizing it from ADP plus hydrogen phosphate ion Anabolic reactions "spend"ATP by transferring a phosphate group to another molecule,thereby regenerating ADP NH2 NH2 Diphosphate Triphosphate HOPO32,H* CH2 -H20 OH OH OHOH Adenosine diphosphate(ADP) Adenosine triphosphate(ATP) Cangage Learing.All Rights Resarved
ATP, the final result of food catabolism, has been called the “energy currency” of the cell ▪ Energy production and use in living organisms revolve around the ATP ⇆ ADP interconversion ▪ Catabolic reactions “buy” ATP with energy released by synthesizing it from ADP plus hydrogen phosphate ion ▪ Anabolic reactions “spend” ATP by transferring a phosphate group to another molecule, thereby regenerating ADP An Overview of Metabolism and Biochemical Energy
An Overview of Metabolism and Biochemical Energy ADP and ATP are phosphoric acid anhydrides O a Contain linkage in carboxylic acid anhydrides React with alcohols by breaking a P-O bond and forming a phosphate ester,ROPO32-.The reaction is a nucleophilic acyl substitution at phosphorus Phosphorylation reactions with ATP require the presence of divalent metal cation in the enzyme,usually Mg2+,to form a Lewis acid-base complex with the phosphate oxygen atoms and neutralize some negative charge H 0 Adenosine Adenosine ATP Mg2+ 00 B-O-P-0+ OPOP-O-Adenosine +Mg2+ A phosphate ester ADP
ADP and ATP are phosphoric acid anhydrides ▪ Contain linkages analogous to the linkage in carboxylic acid anhydrides ▪ React with alcohols by breaking a P-O bond and forming a phosphate ester, ROPO3 2- . The reaction is a nucleophilic acyl substitution at phosphorus ▪ Phosphorylation reactions with ATP require the presence of divalent metal cation in the enzyme, usually Mg2+,to form a Lewis acid-base complex with the phosphate oxygen atoms and neutralize some negative charge An Overview of Metabolism and Biochemical Energy
An Overview of Metabolism and Biochemical Energy An energetically unfavorable reaction "couples"with an energetically favorable reaction so that the overall free- energy change for the two reactions together is favorable Coupled reactions Imagine that reaction 1 does not occur to any reasonable extent because it has a small equilibrium constant and is energetically unfavorable,the reaction has AG 0 (1)A+m二B+n△G>0 where A and B are the biochemically "interesting"substances undergoing transformation,while m and n are enzyme cofactors, H2O,or other substances
An energetically unfavorable reaction “couples” with an energetically favorable reaction so that the overall freeenergy change for the two reactions together is favorable Coupled reactions ▪ Imagine that reaction 1 does not occur to any reasonable extent because it has a small equilibrium constant and is energetically unfavorable, the reaction has ∆G > 0 (1) A + m B + n ∆G > 0 where A and B are the biochemically “interesting” substances undergoing transformation, while m and n are enzyme cofactors, H2O, or other substances An Overview of Metabolism and Biochemical Energy
An Overview of Metabolism and Biochemical Energy Imagine that the product n can react with substance o to yield p and q in a second,strongly favorable reaction that has a large equilibrium constant and△G<<0: (2)n+0p+9△G<0 Because the two reactions are coupled through n,the transformation of A to B becomes possible When an amount of n is formed in reaction 1,it undergoes a complete conversion in reaction 2,thereby removing it from the first equilibrium and forcing reaction 1 to continually replenish n until the reactant A is gone The two reactions added together have a favorable AG <0 The favorable reaction 2"drives"the unfavorable reaction 1 (1)A+m←→B+H △G>0 (2)H+0一→p+q △G<<0 Net:A+m+0-→B+p+q △G<0 企Laeri'g月ha
Imagine that the product n can react with substance o to yield p and q in a second, strongly favorable reaction that has a large equilibrium constant and ∆G << 0: (2) n + o p + q ∆G << 0 Because the two reactions are coupled through n, the transformation of A to B becomes possible ▪ When an amount of n is formed in reaction 1, it undergoes a complete conversion in reaction 2, thereby removing it from the first equilibrium and forcing reaction 1 to continually replenish n until the reactant A is gone ▪ The two reactions added together have a favorable ∆G < 0 ▪ The favorable reaction 2 “drives” the unfavorable reaction 1 An Overview of Metabolism and Biochemical Energy