Metabolism

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Metabolism

• an introduction
• Chapter 6

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I Metabolism the sum of all chemical processes
within an organism.

• CATABOLIC PATHWAYS
• - release energy by breaking down complex
  molecules to simpler molecules
• ANABOLIC PATHWAYS
• - consume energy to build complicated molecules
  from simpler ones

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Metabolic reactions are often coupled, so that...

• ...energy released from a catabolic reaction can
  be used to drive an anabolic reaction.

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II. Energy Transformation... from one form to
another.

• Energy is the capacity to do work.
• Kinetic Energy is the energy of motion.
• Potential Energy is stored energy that matter has
  because of location or structure.
• Chemical Energy is potential energy stored in
  molecular structure.

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Bioenergetics is the study of how organisms
manage their energy resources.

• Organisms transform energy.
• These energy transformations of life are subject
  to the laws of thermodynamics.

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III. Laws of Thermodynamics

• First Law of Thermodynamics
• Energy can be transferred and transformed, but it
  cannot be created or destroyed.
• or the energy of the universe is constant.
• Second Law of Thermodynamics
• Every energy transfer or transformation makes the
  universe more disordered.
• or every process increases the entropy of the
  universe.

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• The entropy of a system may decrease, but the
  entropy of the system plus its surroundings must
  always increase.
• Living things are open systems therefore energy
  is transferred between the system and the
  surroundings.

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Remember that

• Animals take in complex high energy food
  molecules and extract chemical energy to create
  and maintain order. Living things are organized!
• Animals return to their surroundings simpler
  lower energy molecules (CO2 water)
  and heat.

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IV. What about Free Energy ?

• Free Energy is the part of a systems energy that
  can perform work when temperature is uniform
  throughout the system.
• Its called free energy because it is available
  to do work, not because it can be spent without
  cost to the universe.

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Unstable systems ...

• have more free energy.
• will move toward a more stable state.
• have greater capacity to do work.

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Relationships of Free Energy
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Free Energy and Metabolism

• Exergonic reactions (energy outward) proceed
  with a net release of free energy. They occur
  spontaneously.
• Endergonic reactions (energy inward) absorb free
  energy from the surroundings. They are
  nonspontaneous.

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If a process is spontaneous, then the system
must either

• give up energy
• give up order
• or both.

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Think about the following spontaneous
processes

• water flows downhill
• objects of opposite charge attract
• ice cubes melt at room temperature

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So...

• A process that cannot occur on its own is
  nonspontaneous
• it will happen only if there is an external
  energy source!

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Metabolic disequilibrium is necessary for life
a cell at equilibrium is dead.

• For example,
  during cellular respiration a steady
  supply of high energy reactants such as glucose
  and removal of low energy products such as CO2
  and H2O, maintain the disequibilium necessary for
  respiration to proceed.

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• EXERGONIC RXNS
• Products have less free energy than reactants
• Reaction is energetically downhill
• Spontaneous reaction

• ENDERGONIC RXNS
• Products store more free energy than reactants
• Reaction is energetically uphill
• Nonspontaneous reaction

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V. ATP powers cellular work

• by coupling exergonic reactions with endergonic
  reactions.

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ATP (adenosine triphosphate) the immediate
source of energy that drives cellular work

• Mechanical work --
• such as beating of cilia, muscle contraction,
  cytoplasmic flow, and chromosome movement
• Transport work --
• such as pumping substances across membranes
• Chemical work --
• such as the endergonic process of polymerization

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ATP
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The ATP Cycle Energy released by catabolism is
used to phosphorylate ADP regenerating ATP. ATP
couples the cells energy yielding processes to
the energy-consuming ones.
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VI. Enzymes in review

• Enzymes are biological catalysts that
• end in -ase.
• affect the rate of a reaction but remain
  unchanged by it.
• are complementary to the substrate on which
  they act.

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Enzyme particpates but remains unaltered.
à
à

• dissacharide hydrolase H2O à 2
  monosaccharides hydrolase
• sucrose sucrase H2O à glucose
  fructose sucrase

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The catalytic cycle of an enzyme
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Enzymes have 2 important sites.

• Active site Enzymes are complementary to the
  substrate on which they act. This place where
  the enzyme and substrate match perfectly is the
  active site.
• Allosteric site An enzyme with this second site
  has an allosteric effector which fits in it
  exactly and changes the shape of the active site!
  This will either activate or deactivate the
  enzyme.

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Deactivation by allosteric effector

• substrate
• active site
• enzyme
• allosteric site
• allosteric effector

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Enzymatic Control

• Feedback Inhibition - one of the products acts as
  an allosteric effector, inactivating the enzyme
  when amounts of it are high.
• Competitive Inhibition - occurs when the active
  site is occupied by some other substance. The
  regulatory compound and the substance compete for
  the active site of the compound. Ex sulfa drugs
• Non-competitive Inhibition - chemicals combine
  with enzyme prevent its function. Ex cyanides,
  mercury, nerve gas, lead poisoning

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Feedback Inhibition one of the products acts
as an allosteric effector, inactivating the
enzyme when amounts of it are high.
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Competitive Inhibition occurs when the
active site is occupied by some other substance.
Both the regulatory compound and the substance
compete for the active site of the compound. Ex
sulfa drugs
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Non-competitive Inhibition chemicals combine
with enzyme prevent its function. Ex mercury
nerve gas, lead poisoning
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Factors affecting Enzyme Activity

• 1. Amount of enzyme present
• 2. Amount of substrate present
• 3. Temperature
• 4. pH
• 5. Chemicals

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Environmental factors affecting enzymes activity

• Each enzyme has an optimal (a) temperature and
  (b) pH that favor the active conformation of the
  protein molecule.

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Enzyme Nomenclature

• Least specific
• dehydrogenase
• hydrolase
• dehydrolase
• Moderately specific
• lypase
• carbohydrase
• Very specific
• sucrase
• carbonic anhydrase