metabolism i-chp-15-bioc-361-version-oct-2012 - intro
DESCRIPTION
from Campbell Biochemistry 6th Ed. Intro to metabolsim, catabolism, anabolism, ATP, NAD+, reduction, oxidation etc.TRANSCRIPT
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
The Nature of Metabolism
• Metabolism:Metabolism: the chemical reactions of biomolecules. It is the biochemical basis of life processes• catabolism:catabolism: the breakdown of larger molecules into
smaller ones; an oxidative process that releases energy
• anabolism:anabolism: the synthesis of larger molecules from smaller ones; a reductive process that requires energy
A Comparison of Catabolism and Anabolism• Metabolism is the sum total of the chemical reactions
of biomolecules in an organism
Summary
• In catabolism, 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 anabolism, 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
Coenzymes used in Biologically important Redox Reactions• Conversion of ethanol to acetaldehyde is a two-
electron oxidation
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 portion. 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
The Structures and Redox States of the Nicotinamide Coenzymes
FAD/FADH2
• Flavin adenine dinucleotide (FAD) is also a biological oxidizing agent
• Protons, as well as, electrons are accepted by FAD
The Structures of Riboflavin, Flavin Mono-nucleotide (FMN), and Flavin Dinucleotide (FAD)
Coupling of Production and Use of Energy
• The coupling of energy-producing and energy-requiring 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- bonds that require or release convenient amounts of energy, depending on the direction of the reaction
• ATP is essential high energy bond-containing compound
• Phosphorylation of ADP to ATP requires energy• Hydrolysis of ATP to ADP releases energy
The Phosphoric Anhydride Bonds in ATP are “High Energy” Bonds
ATP
• 4 (-) charges on ATP and 3 on ADP, therefore ATP is less stable.
• Why is ATP less stable, charge-wise, than ADP?• Energy must be expended to put on additional
negative charge on ADP• Also, entropy loss when ADP is phosphorylated
because there is a potential loss of resonance hybridization of inorganic phosphate (Pi) upon phosphorylation of ADP to ATP
Loss of a Resonance-Stabilized Phosphate Ion in Production of ATP
ATP Hydrolysis Decreases in Electrostatic Repulsion• Marked decrease in
electrostatic repulsion of -phosphate of GDP upon hydrolysis of ATP to ADP
Role of ATP as Energy Currency
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
Coenzyme A in Activation of Metabolic Pathways• A step frequently encountered in metabolism is
activation• activationactivation:: the formation of a more reactive
substance • A metabolite is bonded to some other molecule and
the free-energy change for breaking the new bond is negative.
• Causes next reaction to be exergonic
Two Ways of Looking at Coenzyme A
• Coenzyme A (CoA-SH) contains units of 2-2-mercaptoethylaminemercaptoethylamine, pantothenic acid, and 3’,5’-ADP
The Hydrolysis of Acetyl-CoA
• The metabolically active form of a carboxylic acid is the corresponding acyl-CoA thioester, in which the thioester linkage is a high-energy bond
The Role of Electron Transfer and ATP Production in metabolism
Summary
• Metabolic pathways proceed in many stages, allowing for efficient use of energy
• Many coenzymes, particularly coenzyme A(CoA) play a crucial role in metabolism