INTRODUCTION TO METABOLISM'

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INTRODUCTION TO METABOLISM.

• Chapter 6
• Metabolism, Energy, and Life

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Objectives

• Explain the role of catabolic and anabolic
  pathways in cell metabolism
• Distinguish between kinetic and potential energy
• Distinguish between open and closed systems
• Explain the first and second Laws of
  Thermodynamics
• Distinguish between entropy and enthalpy
• Understand the Gibbs equation for free energy
  change
• Understand how usable energy changes with
  changes in enthalpy, entropy, and temperature
• Understand the usefulness of free energy

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Metabolism

• The sum of all the chemical processes occurring
  in an organism at one time
• Concerned with the management of material and
  energy resources within the cell
• Catabolic pathways
• Anabolic pathways

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Catabolic Pathways

• Pathways that release energy by breaking down
  complex molecules into simpler compounds
• Cellular respiration
• C6H1206 6O2?6CO2 6H20 ENERGY

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Anabolic Pathways

• Pathways that consume energy to build larger,
  complicated molecules from simpler ones
• Polymerization
• Photosynthesis6CO2 6H20 light ? C6H1206 6O2

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Bioenergetics

• Study of how organisms manage their energy
  resources
• Energy is the capacity to do work, to move matter
• Kinetic energy energy that is in motion
• Potential energy stored energy based on location
  or structure
• The rearrangement of atoms in molecules may
  result in the potential energy of the molecule
  being converted into kinetic energy

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Energy LawsLaws of Thermodynamics

• The terms open or closed systems refer to whether
  or not energy can be transferred between the
  system and its surroundings (can energy be
  imported or exported)
• First Law of Thermodynamics Energy can neither
  be created nor destroyed, only transformed from
  one type to another
• Second Law of Thermodynamics Each energy
  transformation results in less usable (ordered)
  energy

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Free EnergyGH-TS
Free energy (G) is the portion of system energy
that can do work under uniform temperature

• Enthalpy or work total energy is a measure of all
  the energy in a system
• Symbolically represented as H

• Entropy is a measure of randomness (disorder)
• Symbolically represented as S

Temperature (T) is measured in 0K
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?G

• The higher the G the more unstable the system
• A change in free energy can occur with metabolism
• Exergonic reactions that lose energy -?G
• Endergonic reactions that gain energy ?G
• Metabolic reactions are often coupled where an
  exergonic reaction might fuel an endergonic
  reaction
• When ?G 0 no work can be done
• When reactions go to equilibrium, ?G
  0(therefor metabolic reactions do not usually
  reach an equilibrium)
• Energy needed for Mechanical, Chemical, and
  Transport workings of the cell

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Objectives

• Explain the role of ATP in the cell
• Describe ATPs composition and how it performs
  cellular work
• Explain the importance of chemical disequilibrium
• Understand the energy profile of a reaction
  including activation energy, free energy change,
  transition state
• Describe the role and mechanisms of enzymes
• Explain how enzyme activity can be controlled by
  environmental factors, cofactors, enzyme
  inhibitors, and allosteric regulators
• Distinguish between allosteric activation and
  cooperativity
• Explain how metabolic pathways are regulated

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ATP

• Energy molecule used to couple exergonic
  reactions to endergonic
• Nucleotide with three phosphate groups attached
  to the ribose sugar
• ATP has a high ?G

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ATP

• Energy is released from ATP through the loss of
  phosphate groups
• Catabolic reaction resulting from hydrolysis
  producing ADP Pi (inorganic Phosphate) energy
  (?G -7.3Kcal/mol in the lab, -13Kcal/mol in
  the cell)

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How ATP works

• Hydrolysis of ATP produces inorganic phosphate
  that is attached to a molecule involved in an
  endergonic process
• Phosphorylation is the process of ATP
  transferring phosphate to a molecule
• Results in a phosphorylated intermediate

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Regeneration of ATP

• ATP loses energy when it phosphorylates an
  intermediate molecule of an endergonic reaction.
  ATP becomes ADP
• Regeneration of ATP occurs when inorganic
  phosphate (Pi) is bound to ADP utilizing energy
  supplied by a catabolic reaction

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Cell Efficiency

• ATP is a good energy source because
• It can participate in a many different kinds of
  reactions within the cell
• Usually is directly involved in reactions
• Little wasted energy during phosphorylation of an
  intermediate
• Enzymes
• Regulation of reactions

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Enzymes

• Enzymes are proteins
• Specific because of conformational shape
• Enzymes are catalysts
• Catalyst chemical that changes the rate of a
  reaction without being consumed
• Recycled
• Enzymes reduce the activation energy of a
  reaction
• Amount of energy that must be added to get a
  reaction to proceed

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Activation Energy

• EA Activation energy
• EA is usually supplied by heat
• Reactants absorb heat increasing ?G making the
  reactants unstable so they react

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How Enzymes Function

• Enzymes are substrate specific
• Substrate any molecule to which an enzyme will
  bind
• Although an enzyme can be a large protein, only a
  specific region of the enzyme interacts with the
  substrate
• Active Site region of enzyme that reacts to
  substrate
• As enzyme and substrate bind, the enzyme shape is
  modified to better fit the substrate
• Induced fit occurs as a result of the enzyme
  substrate complex

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Enzyme activity

• The rate at which an enzyme can function is
  dependant on several factors including
• Temperature
• pH
• The rate of reaction is also influenced by the
  concentration of the substrate or enzyme
• Some enzymes utilize inorganic or organic
  molecules as helpers
• Cofactor inorganic molecule (mineral)
• Coenzyme organic non-protein molecule (vitamin)

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Enzyme Inhibitors

• Enzyme activity may be reduced by molecules
  attaching to the enzyme.
• Inhibition may occur at two different locations
• competitive inhibition inhibitor mimics molecule
  that attaches to active site
• noncompetitive inhibition inhibitor binds to
  enzyme away from the active site resulting in
  modification of active site

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Control of Metabolism

• Allosteric Regulation enzyme function may be
  stimulated or inhibited by attachment of
  molecules to an allosteric site
• Feedback Inhibition end product of metabolic
  pathway may serve as allosteric inhibitor
• Cooperativity single substrate molecule primes
  multiple active sites increasing activity

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