An Introduction to Metabolism

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Chapter 8

• An Introduction to Metabolism

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Organization of the Chemistry of Life into
Metabolic Pathways

• A metabolic pathway has many steps
• That begin with a specific molecule and end with
  a product
• That are each catalyzed by a specific enzyme

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• Catabolic pathways
• Break down complex molecules into simpler
  compounds
• Release energy

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• Anabolic pathways
• Build complicated molecules from simpler ones
• Require energy input

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Forms of Energy

• Energy
• Exists in various forms
• Some forms of energy can perform work

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Forms of Energy

• Kinetic energy
• Is the energy associated with motion
• Potential energy
• Is stored in the location of matter
• Includes chemical energy stored in molecular
  structure (e.g., food)

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The First Law of Thermodynamics

• According to the first law of thermodynamics
• Energy can be transferred and transformed
• Energy cannot be created or destroyed

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• An example of energy conversion
• Plants convert the energy in sunlight to
  synthesize sucrose.

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Free-Energy Change, ?G

• A living systems free energy
• Is energy that can do work under cellular
  conditions

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• If the change in free energy, ?G, during a
  biological process is negative then the reaction
  will proceed spontaneously.

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Exergonic and Endergonic Reactions in Metabolism

• An exergonic (catabolic) reaction
• Proceeds with a net release of free energy and is
  spontaneous

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• An endergonic (anabolic) reaction
• Is one that requires free energy input and is
  nonspontaneous

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ATP is the Chief Energy Molecule of Cells

• Basic Concept ATP drives anabolic
  (endergonic/uphill) reactions

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The Structure and Hydrolysis of ATP

• ATP (adenosine triphosphate)
• Provides energy for cellular functions

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• Energy is released from ATP
• When the terminal phosphate bond is broken

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A Coupled Reaction

• ATP hydrolysis
• Can be coupled to other reactions

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How ATP Performs Work

• ATP drives endergonic reactions
• By phosphorylation, i.e., transferring a
  phosphate to other molecules
• Glu ATP ? Glu-P ADP
• Glu-P NH3 ? Gln P
• Overall
• Glu NH3 ? Gln ?G - 3.9 kcal/mol

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• The three types of cellular work
• Are powered by the hydrolysis of ATP

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The Regeneration of ATP

• Energy yielding (catabolic) pathways are used to
  regenerate ATP from ADP and phosphate
• 107 molecules of ATP used syn. /second/cell