The Generation of Biochemical Energy

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Chapter 21

• The Generation of Biochemical Energy

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Energy and Life

• Energy is required for all of lifes functions
  (e.g. mechanical work, chemical synthesis, moving
  molecules within cells)

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Energy and Life

• The energy required by humans is released from
  the food that we eat
• Food contains stored energy
• Our body breaks down food through a combustion
  reaction
• Generates a lot of energy
• Energy must be released from food gradually
• Energy must be stored in accessible forms

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Energy and Life

• Release of energy from storage must be finely
  controlled so that it is available exactly when
  and where it is needed.
• Just enough energy must be released as heat to
  maintain constant body temperature.
• Energy in a form other than heat must be
  available to drive chemical reactions that are
  not favorable at body temperatures.

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Energy and Life
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Energy and Biochemical Reactions

• Review Energy of Chemical Reactions Chapter 7
• A favorable chemical reaction involves the
  release of energy exergonic reaction
• ?G must be negative
• ?G ?H - T ?S
• Do not confuse exergonic with exothermic.
• Exothermic simply describes energy released in
  the form of heat
• But a reaction can be endothermic and still be
  exergonic because ?G relies on heat and degree of
  disorder

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Energy and Biochemical Reactions

• Review of Chemical Energy
• An endergonic reaction, unfavorable reaction, is
  a reaction in which energy must be absorbed in
  order for the reaction to proceed
• ?G will be positive
• Again an endothermic reaction ?H is not the
  same as an endergonic reaction

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Energy and Biochemical Reactions
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Energy and Biochemical Reactions
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Cells and Their Structure

• There are two main categories of cells
• prokaryotic cells, usually found in single-celled
  organisms including bacteria and blue-green algae
• eukaryotic cells, found in some single-celled
  organisms and all plants and animals.

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An Overview of Metabolism and Energy Production

• Together, all of the chemical reactions that take
  place in an organism constitute its metabolism.
• Metabolic pathways may be linear, cyclic, or
  spiral.

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An Overview of Metabolism and Energy Production

• Catabolism Metabolic reaction pathways that
  break down food molecules and release biochemical
  energy.
• Anabolism Metabolic reactions that build larger
  biological molecules from smaller pieces.

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Strategies of Metabolism ATP and Energy Transfer

• ATP is an energy transporting material
• Adenosine Triphosphate

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Strategies of Metabolism ATP and Energy Transfer

• ATP is an energy transporter because its
  production from ADP requires an input of energy
  that is stored and released wherever needed.
• Biochemical energy is gathered from exergonic
  reactions that produce ATP. The ATP then travels
  to where energy is needed, and through hydrolysis
  releases the energy for whatever work must take
  place.

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Strategies of Metabolism Metabolic Pathways and
Coupled Reactions

• Not every kind of metabolic reaction is
  spontaneous
• ADP ? ATP ?G 7.3 kcal/mol
• The metabolic strategy for dealing with what
  would be an energetically unfavorable reaction is
  to couple it with an energetically favorable
  reaction so that the overall energy change for
  the two reactions is favorable.

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Strategies of Metabolism Metabolic Pathways and
Coupled Reactions
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Strategies of Metabolism Metabolic Pathways and
Coupled Reactions

• The energy provided by an exergonic reaction is
  either released as heat or stored as chemical
  potential energy in the bonds of products of the
  coupled endergonic reaction.

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Strategies of Metabolism Oxidized and Reduced
Coenzymes

• The net result of catabolism is the oxidation of
  food to release energy.
• Many metabolic reactions are oxidationreduction
  reactions.
• Oxidation can be loss of electrons, loss of
  hydrogen, or gain of oxygen.
• Reduction can be gain of electrons, gain of
  hydrogen, or loss of oxygen.
• Oxidation and reduction always occur together.

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Strategies of Metabolism Oxidized and Reduced
Coenzymes

• A steady supply of oxidizing and reducing agents
  must be available, so a few coenzymes
  continuously cycle between their oxidized and
  reduced forms.

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Strategies of Metabolism Oxidized and Reduced
Coenzymes

• Example Consider reaction of malate to form
  oxaloacetate from the Citric Acid (Krebs) Cycle

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Strategies of Metabolism Oxidation and Reduction
of Coenzymes

• Because the reduced coenzyme NADH have picked up
  electrons to form the H-C bond, they are referred
  to as electron carriers (21.9)

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Citric Acid Cycle
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The Electron-Transport Chain and ATP Production

• At the conclusion of the citric acid cycle, the
  reduced coenzymes formed in the cycle are ready
  to donate their energy to making additional ATP.

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Harmful Oxygen By-Products and Antioxidant
Vitamins

• More than 90 of the oxygen we breathe is used in
  electron transportATP synthesis reactions.
• In these and other oxygen-consuming redox
  reactions, the product may not be water, but one
  or more of three highly reactive species.

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Harmful Oxygen By-products and Antioxidant
Vitamins

• Protection
• Enzymes such as catalase
• Vitamins E, C, and A

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Homework

• 21.1-21.9, 21.11-21.16, 21.18, 21.19,
  21.21-21.26, 21.28, 21.30, 21.32, 21.38, 21.40,
  21.44, 21.46, 21.48, 21.50, 21.52, 21.54, 21.56,
  21.58, 21.60, 21.62, 21.64, 21.66, 21.68, 21.72,
  21.76