Metabolism Is the Sum of Cellular Reactions

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Metabolism Is the Sum of Cellular Reactions

• Metabolism - the entire network of chemical
  reactions carried out by living cells
• Metabolites - small molecule intermediates in the
  degradation and synthesis of polymers
• Catabolic reactions - degrade molecules to create
  smaller molecules and energy
• Anabolic reactions - synthesize molecules for
  cell maintenance, growth and reproduction

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Fig 10.1 Anabolism and catabolism
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Common themes of organisms
1. Organisms or cells maintain specific internal
concentrations of inorganic ions, metabolites and
enzymes 2. Organisms extract energy from external
sources to drive energy-consuming reactions 3.
Organisms grow and reproduce according to
instructions encoded in the genetic material

• 4. Organisms respond to environmental influences
• 5. Cells are not static, and cell components are
  continually synthesized and degraded (i.e.
  undergo turnover)

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Fig 10.2 Forms of metabolic pathways
Linear Cyclic
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Metabolic Pathways Are Regulated

• Metabolism is highly regulated to permit
  organisms to respond to changing conditions
• Most pathways are irreversible
• Flux - flow of material through a metabolic
  pathway. Flux depends upon (1) Supply of
  substrates (2) Removal of products (3) Pathway
  enzyme activities

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Feedback inhibition

• Product of a pathway controls the rate of its own
  synthesis by inhibiting an early step (usually
  the first committed step (unique to the
  pathway)

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Feed-forward activation

• Metabolite early in the pathway activates an
  enzyme further down the pathway

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Major Pathways in Cells

• Metabolic fuels
• Three major nutrients consumed by mammals
• (1) Carbohydrates - provide energy(2) Proteins
  - provide amino acids for protein synthesis and
  some energy(3) Fats - triacylglycerols provide
  energy and also lipids for membrane synthesis

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Fig 10.5

• Overview of catabolic pathways

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Catabolism produces compounds for energy
utilization

• Three types of compounds are produced that
  mediate the release of energy
• (1) Acetyl CoA (2 carbon units for metabolism)
• (2) Nucleoside triphosphates (ATP or GTP)
• (3) Reduced coenzymes (NADH, FADH2, QH2)

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The Free Energy of ATP

• Energy from oxidation of metabolic fuels is
  largely recovered in the form of ATP

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Fig 10.7

• Hydrolysis of ATP

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ATP is an energy-rich compound

• A large amount of energy is released in the
  hydrolysis of the phosphoanhydride bonds of ATP
  (and UTP, GTP, CTP)
• All nucleoside phosphates have nearly equal
  standard free energies of hydrolysis

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Energy source of phosphoanhydrides
(1) Electrostatic repulsion among negatively
charged oxygens of phosphoanhydrides of ATP (2)
Solvation of products (ADP and Pi) or (AMP and
PPi) is better than solvation of reactant ATP (3)
Products are more stable than reactants There
are more delocalized electrons on ADP, Pi or AMP,
PPi than on ATP
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Enzymatic reactions often require ATP energy to
drive reactions
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Reduced Coenzymes Conserve Energy from Biological
Oxidations
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Fig 10.1 Anabolism and catabolism
Glucose
ATP
CO2
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Fig 11.1

• Catabolism of glucose via glycolysis and the
  citric acid cycle

NADH
NADH, FADH2
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Table 11.1
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Fig 10.5

• Overview of catabolic pathways

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