Topic 4' Metabolism

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Topic 4. Metabolism
September 28, 2005 Biology 1001
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4.1 Introduction to Metabolism

• Metabolism is the totality of an organisms
  chemical reactions
• Reactions are arranged in metabolic pathways or
  series where each step is catalyzed by an enzyme

• Metabolic pathways are either catabolic or
  anabolic
• Catabolic pathways are degradative, and release
  energy
• Anabolic pathways consume energy to build larger
  molecules from smaller ones

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Chemistry Thermodynamics

• Bioenergetics is the study of how organisms
  manage their energy resources
• Energy is the capacity to cause change. Forms of
  energy include
• Kinetic the energy of motion
• Thermal the random kinetic energy of atoms or
  molecules
• Potential the energy of location or structure
• Chemical the potential energy of molecules
  during a chemical reaction
• Thermodynamics is the study of energy
  transformation
• The first law of TD - the energy of the universe
  is constant
• The second law of TD energy transformation
  increases the entropy or randomness of the
  universe
• Living organisms increase entropy despite
  biological order

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Chemistry Thermodynamics
PE KE
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4.2 - ATP Powers Cellular Work

• Work involves using energy to move matter against
  opposing forces
• Organisms perform three kinds of work
• Mechanical, transport, chemical
• To do work organisms couple endergonic reactions
  with exergonic ones, a process called energy
  coupling
• The molecule used to power cellular work by
  energy coupling is adenosine triphosphate - ATP

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ATP
A high-energy bond
Figure 8.9 ATP Hydrolysis
Figure 8.8 The Structure of ATP
An exergonic reaction
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Energy Coupling
The exergonic hydrolysis of ATP is coupled to an
endergonic reaction by way of a phosphorylated
intermediate
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The Regeneration of ATPThe ATP Cycle

• ADP gets phosphorylated back to ATP using energy
  released by catabolic reactions in the cell and
  inorganic phosphate
• This shuttling of inorganic phosphate and energy
  from ATP to an intermediate and back to ATP is
  the ATP cycle

Fig. 8.12
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4.4 Enzymes and Metabolism(We will do Topic 4.3
with Topic 9)

• A catalyst is a chemical agent that speeds up a
  reaction without itself being consumed
• An enzyme is a protein that functions as a
  biological catalyst
• Both exergonic and endergonic reactions require
  enzymes to occur at appropriate rates in the cell
• This is because of the activation energy required
  to get a reaction started
• Enzymes lower the activation energy barrier and
  allow reactions to proceed more quickly

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How Enzymes Work
Figures 8.14 8.15
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How Enzymes Work - The Catalytic Cycle
Figure 8.17 - The active site and the catalytic
cycle of an enzyme
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Features of the Catalytic Cycle

• The reactant that an enzyme acts on is called a
  substrate
• The enzyme binds to the substrate forming an
  enzyme-substrate complex
• Only a restricted part of the enzyme usually
  binds to the substrate the active site
• Binding to the active site may involve induced
  fit
• Enzymes use a variety of mechanisms to lower
  activation energy
• When the products are released the enzyme is free
  to enter another cycle

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More About Enzymes

• Enzymes are substrate- and reaction-specific
• Enzymes catalyze reactions in both directions,
  depending on the relative concentration of
  reactants vs. products
• Enzymes do not change the overall energy of the
  reaction
• Enzymes may require cofactors, called coenyzmes
  if they are organic molecules
• Enzymes are affected by environmental factors
  such as temperature and pH

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Temperature and pH affect enzyme activity

• Each enzyme has an optimal temperature at which
  its reaction rate is greatest, one that allows
  the greatest number of molecular collisions but
  does not denature the enzyme
• 35-40oC for humans, 70oC for prokaryotes living
  in hot springs
• Similarly, enzymes operate best at their optimal
  pH, usually between 6 and 8