from Campbell Biochemistry 6th Ed. Intro to metabolsim, catabolism, anabolism, ATP, NAD+, reduction, oxidation etc.

1. Mary K. Campbell
Shawn O. Farrell
http://academic.cengage.com/chemistry/campbell
Chapter 15
The Importance of Energy Changes and
Electron Transfer in Biology
Paul D. Adams • University of Arkansas

2. The Nature of Metabolism
• Metabolism: the chemical reactions of
biomolecules. It is the biochemical basis of life
processes
• catabolism: the breakdown of larger molecules into
smaller ones; an oxidative process that releases
energy
• anabolism: the synthesis of larger molecules from
smaller ones; a reductive process that requires energy

3. A Comparison of Catabolism and
Anabolism
• Metabolism is the sum total of the chemical reactions
of biomolecules in an organism

4. 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

5. Coenzymes used in Biologically important
Redox Reactions
• Conversion of ethanol to acetaldehyde is a two-
electron oxidation

6. 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

7. The Structures and Redox States of the
Nicotinamide Coenzymes

8. FAD/FADH2
• Flavin adenine dinucleotide (FAD) is also a biological
oxidizing agent
• Protons, as well as, electrons are accepted by FAD

9. The Structures of Riboflavin, Flavin Mono-
nucleotide (FMN), and Flavin Dinucleotide (FAD)

10. 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

11. The Phosphoric Anhydride Bonds in ATP
are “High Energy” Bonds

12. 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

13. Loss of a Resonance-Stabilized Phosphate
Ion in Production of ATP

14. ATP Hydrolysis Decreases in Electrostatic
Repulsion
• Marked decrease in
electrostatic repulsion
of β-phosphate of
GDP upon hydrolysis of
ATP to ADP

15. Role of ATP as Energy Currency

16. 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

17. Coenzyme A in Activation of Metabolic
Pathways
• A step frequently encountered in metabolism is
activation
• activation: 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

18. Two Ways of Looking at Coenzyme A
• Coenzyme A (CoA-SH) contains units of 2-
mercaptoethylamine, pantothenic acid, and 3’,5’-
mercaptoethylamine
ADP

19. 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

20. The Role of Electron Transfer and ATP
Production in metabolism

21. 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