Chapter 13.1: Bioenergetics and Thermodynamics

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Chapter 13.1Bioenergetics and Thermodynamics

• CHEM 7784
• Biochemistry
• Professor Bensley

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Introduction and Chapter 13.1Bioenergetics and
Thermodynamics
Todays Objectives To learn and understand the

• Differences between metabolic, catabolic, and
  anabolic processes
• Thermodynamic applications to metabolic processes
  

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Bioenergetics and Thermodynamics

• Bioenergetics the quantitative study of energy
  transductions (changes from one form to another)
• First Law of Thermodynamics conservation of
  energy

• Second Law of Thermodynamics universe always
  tends towards increasing disorder

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Laws of Thermodynamics Apply to Living Organisms

• In order to maintain organization within the
  themselves, living systems must be able to
  extract useable energy from the surrounding, and
  release useless energy (heat) back to the
  surrounding (Open systems)

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Mathematical Relationships

• ?G ?H - T?S
• Standard free-energy change (?G0) standard
  conditions (298K, 1 atm, 1M initial for both
  reactants and products)
• Biochemical standard state says that H 10-7
  and H2O 55.5 M
• Physical constants based on biochemical standard
  state are written with a prime such as ?G0 and
  Keq

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Mathematical Relationships

• ?G0 -RT ln Keq

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Mathematical Relationships

• ?G is a constant but ?G0 is a function of
  concentrations and temperature
• ?G ?G0 RT ln CcDd
• 
  AaBb
• Spontaneity of a reaction is determined by value
  of ?G not ?G0
• Some thermodynamically favorable reactions do not
  occur at measurable rates (combustion of
  firewood) so they need to be catalyzed (enzymes)

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Mathematical Relationships

• Standard free-energy changes are additive in the
  case of two sequential reactions
• Because of this, the idea of coupling a highly
  exergonic reaction to an thermodynamically
  unfavorable one happens
• Example (Glucose 6-phosphate formation)
• Equilibrium constants are multiplicative in the
  case of two sequential reactions

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Hydrolysis Reactions tend to be Strongly
Favorable (Spontaneous)
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Complete Oxidation of Reduced Compounds is
Strongly Favorable

• This is how chemotrophs obtain most of their
  energy
• In biochemistry the oxidation of reduced fuels
  with O2 is stepwise and controlled
• Recall that being thermo-dynamically favorable is
  not the same as being kinetically rapid