The Living World Chapter 5

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An Introduction to Metabolism Chapter 8
Associate Professor Pamela L. Pannozzo Principles
of Biology I BSC 1010
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Metabolism

• Metabolism sum of an organisms chemical
  reactions
• Metabolic pathway a series of chemical
  reactions taking place inside a cell that convert
  molecules to end products
• Catalyzed by enzymes

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Metabolic Pathway

• Catabolic pathway breaks down molecules, may
  release energy
• Anabolic pathway builds complex molecules,
  consumes energy

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Energy

• The ability to do work
• Exists in two states kinetic and potential

Kinetic Energy energy of motion
Potential Energy stored energy
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Forms of Energy

• Energy exists in many forms
• Mechanical, sound, light, electric, heat,
  chemical, etc.
• Heat (thermal) energy form of kinetic energy
  associated with the random movement of molecules
• Chemical energy form of potential energy held
  in the bonds between atoms of a molecule

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Laws of Thermodynamics

• The First Law
• Energy cannot be created or destroyed but it can
  change forms
• During each conversion, some energy is lost into
  the environment as heat energy
• The Second Law of Thermodynamics
• Disorder (entropy) in closed systems is
  continuously increasing
• Each energy transformation increases the entropy
  of the universe

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Spontaneity of Chemical Reactions

• Some chemical reactions occur spontaneously,
  others occur only with an initial input of energy
• Based on free energy changes
• Free Energy G the amount of energy that is
  available to perform work in a cell
• unstable energy
• Measure to determine if a reaction will occur
  spontaneously or not
• ?G ?H T?S
• H total energy
• T temperature
• S entropy

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Spontaneity of Chemical Reactions (cont)

• Spontaneous reactions occur only if the system
  gives up energy or order, or both only where ?G
  is negative
• Systems move toward greater stability, less free
  energy, or equilibrium

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Spontaneity of Chemical Reactions (cont)

• Exergonic reaction net release of free energy
• Occurs spontaneously
• C6H12O6 O2 ? 6CO2 6 H2O ATP heat
• ?G -686 kcal/mol
• Endergonic reaction absorbs energy from its
  surroundings
• Does not occur spontaneously
• Stores free energy in molecules

6CO2 6 H2O sunlight energy ? C6H12O6 O2 ?G
686 kcal/mol
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The Flow of Energy in Living Things

• Sun to Autotrophic organisms
• Capture part of it (2), convert to potential
  chemical energy in the bonds between atoms of
  monosaccharides
• Within Autotrophs and to Heterotrophs
• Heterotrophs consume autotrophs, convert
  monosaccharides into a smaller molecule that
  cells can use called adenosine triphosphate (ATP)

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ATP The Energy Currency of the Cell
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ATP Hydrolysis
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Phosphorylation
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ATP Powers Cellular Work

• Protein synthesis
• Muscle cell contractions
• Vesicular transport

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ATP Powers Cellular Work

• Active transport
• Temperature
• homeostasis
• Ciliar/flagellar
• movements

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ATP Powers Cellular Work

• Protein activation
• Cell shape
• changes

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Enzymes

• Catalyze metabolic reactions that make or break
  molecules
• Activation energy (EA) energy needed to start a
  chemical reaction
• to change the shape of the molecules
• usually heat from surroundings

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Activation Energy
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Enzymes (cont)

• Enzymes lower EA barrier without addition of heat
• Protection of proteins
• Selective metabolic control
• Direction of catalysis determined by amount of
  substrate and enzyme

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Effects on Enzyme Activity

• Temperature
• pH
• Cofactors
• Enzyme inhibitors

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Regulation of Enzyme Activity

• Cofactors/Coenzymes
• Metal ions or organic molecules
• Bind to enzymes or substrates
• Inhibitors
• Permanent inhibition ? covalently bonded to
  enzyme
• Reversible inhibition ? weakly bonded to enzyme
• Competitive inhibitors--resemble substrate
• Noncompetitive inhibitors--bind to non-active
  site area, alter enzyme shape

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Regulation of Enzyme Activity (cont)

• Allosteric Regulation
• proteins function at one site is affected by
  binding of a regulatory molecule at another site
• stimulates or inhibits enzyme
• Feedback Inhibition
• inhibits enzyme

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Regulation of Enzyme Activity (cont)

• Specific Within-Cell Localization
• Enzyme complexes with fixed locations in the cell
• Intermembrane
• Within-organelles