Download - Standard States for Free-Energy Changes
![Page 1: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/1.jpg)
Chapter 15The Importance of Energy Changes and
Electron Transfer in Biology
Mary K. CampbellShawn O. Farrellhttp://academic.cengage.com/chemistry/campbell
Paul D. Adams • University of Arkansas
![Page 2: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/2.jpg)
Standard States for Free-Energy Changes
• Standard states• for pure solids and liquids, _____________________• for gases, the gas at _____________________• for solutions, a concentration __________________
• For the reaction
We can rewrite the equation that relates the G for the reaction under any conditions to the free-energy change under standard conditions (G˚)
![Page 3: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/3.jpg)
Standard States for Free-Energy Changes (Cont’d)
• When the reaction is at equilibrium, G = _____
• If we can determine the concentration of reactants and products at equilibrium, we can determine Keq and, from it, the change in free energy for conversion of one mole of reactant to product(s)
![Page 4: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/4.jpg)
Modified Standard State for Biochemical Rxns
• Standard free energy change, G°, assumes a molar concentration of 1 M• if [H+] = 1 M, then pH = _____• but the pH in most cells is near the neutral range
• For biochemical reactions, we define a different standard state for the concentration of H+
• standard state for [H+] = _____________________• this modified standard state is given the symbol
• SummaryThe usual thermodynamic standard state implies that the system involved is at pH=0, which is seldom, if ever, found in living things. The modified standard state explicitly states that the system is at pH=7
![Page 5: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/5.jpg)
Biochemical Connections: Thermodynamics
![Page 6: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/6.jpg)
The Nature of Metabolism
• _____________:_____________: the chemical rxns of biomolecules • Metabolism Metabolism is the biochemical basis of• _____________:_____________: the breakdown of larger molecules
into smaller ones; an oxidative process that releases energy
• _____________:_____________: the synthesis of larger molecules from smaller ones; a reductive process that requires energy
![Page 7: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/7.jpg)
A Comparison of Catabolism and Anabolism
• Metabolism is the sum total of the biochemical reactions in an organism
![Page 8: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/8.jpg)
The Role of Oxidation and Reduction in Metabolism
• Oxidation-Reduction reactions are those in which electrons are transferred from a donor to an acceptor• ________:________: the loss of electrons; the substance that
loses the electrons is called a ________ agent________ agent• ________:________: the gain of electrons; the substance that
gains the electrons is called an ________ agent________ agent
• Carbon in most reduced form- ______________________• Carbon in most oxidized form- ___________ ___________
(final product of catabolism
![Page 9: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/9.jpg)
Summary
• In ________________, large molecules are broken down to smaller products, releasing energy and transferring electrons to acceptor molecules of various sorts. The overall process is one of oxidation.
• In ________________, small molecules react to give rise to larger ones; this process requires energy and involves acceptance of electrons from a variety of donors. The overall process is one of reduction
![Page 10: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/10.jpg)
Coenzymes used in Biologically important Redox Rxns
• Conversion of ethanol to acetaldehyde is a two-electron oxidation
![Page 11: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/11.jpg)
NAD+/NADH: An Important Coenzyme
• Nicotinamide adenine dinucleotide (NAD+) is an important coenzyme
• Acts as a biological oxidizing agent• The structure of NADH is comprised of a
nicotinamide moiety. It is involved in the reaction. It is a derivative of nicotinic acid
• NAD+ is a two-electron oxidizing agent, and is reduced to NADH
![Page 12: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/12.jpg)
Structures & Redox States of Nicotinamide Coenzymes
![Page 13: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/13.jpg)
FAD/FADH2
• Flavin adenine dinucleotide (FAD) is also a biological ______________ agent
• Protons and electrons are accepted by FAD
![Page 14: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/14.jpg)
The Structures of Riboflavin, Flavin Mononucleotide (FMN), and Flavin Dinucleotide (FAD)
![Page 15: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/15.jpg)
Coupling of Production and Use of Energy
• The coupling of ________-____________ and ________-____________ reactions is a central theme in the metabolism of all organisms
• Energy cannot be used directly, must by shuttled into easily accessible forms of chemical energy
• “High Energy” bonds require or release convenient amounts of energy, depending on the direction of the reaction
• ______ is an essential high energy bond-containing compound
• Phosphorylation of ADP to ATP _________ energy• Hydrolysis of ATP to ADP _________ energy
![Page 16: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/16.jpg)
The Phosphoric Anhydride Bonds in ATP
“High Energy” Bonds are in red
![Page 17: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/17.jpg)
ATP
• Four – charges on ATP and 3 on ADP, therefore ATP is ______________ ______________ .
• Why is ATP less stable, charge-wise, than ADP?• Energy must be expended to put an additional
___________________________________________• Also, entropy loss when ADP is phosphorylated
because there is a potential loss of ______________ ______________ of inorganic phosphate (P i) on phosphorylation of ADP to ATP
![Page 18: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/18.jpg)
Loss of a Resonance-Stabilized Phosphate Ion
…in Production of ATP
![Page 19: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/19.jpg)
ATP Hydrolysis Decreases Electrostatic Repulsion
• Marked decrease in ________________ _______________ of -phosphate of GDP
upon hydrolysis of ATP to ADP
![Page 20: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/20.jpg)
Role of ATP as Energy Currency
![Page 21: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/21.jpg)
Summary
• Hydrolysis of ATP to ADP releases energy
• In the coupling of biochemical reactions, the energy released by one reaction, such as ATP hydrolysis, provides energy for another
![Page 22: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/22.jpg)
CoA in Activation of Metabolic Pathways
• A step frequently encountered in metabolism is activation• activationactivation:: the formation of a ___________________
substance • A metabolite is bonded to some other molecule and
the free-energy change for breaking the new bond is ______________ .
• Causes next reaction to be ______________
![Page 23: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/23.jpg)
Two Ways of Looking at Coenzyme A
Coenzyme A (CoA-SH) contains pantothenic acid, 3’,5’-ADP and 2-mercaptoethylamine2-mercaptoethylamine
![Page 24: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/24.jpg)
The Hydrolysis of Acetyl-CoA
The metabolically active form of a carboxylic acid is the acyl-CoA thioester with a high-energy thioester bond
![Page 25: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/25.jpg)
The Role of Electron Transfer & ATP Production in Metabolism
![Page 26: Standard States for Free-Energy Changes](https://reader035.vdocuments.site/reader035/viewer/2022081519/5681359b550346895d9d0cf2/html5/thumbnails/26.jpg)
Summary
• Metabolic pathways proceed in many stages, allowing for efficient use of energy
• Many coenzymes, particularly coenzyme A(HS-CoA) play a crucial role in metabolism