Metabolism: Energy and Enzymes

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Metabolism Energy and Enzymes

• Chapter 6

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Outline

• Forms of Energy
• Laws of Thermodynamics
• Metabolic Reactions
• ATP
• Metabolic Pathways
• Energy of Activation
• Enzymes
• Photosynthesis
• Cellular Respiration

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Forms of Energy

• Kinetic - Energy of motion.
• Mechanical
• Potential - Stored energy.
• Chemical

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Laws of Thermodynamics

• First law (law of conservation of energy) states
  
• Energy cannot be created or destroyed, but it can
  be changed from one form to another.
• Second law states
• Energy cannot be changed from one form to another
  without a loss of usable energy.

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Cells and Entropy

• Second law can also be explained as every energy
  transformation makes the universe less organized
  and more disordered.
• Entropy
• Second law means that every cellular process
  increases the total entropy of the universe.

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Cells and Entropy
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Metabolic Reactions

• Metabolism - Sum of cellular chemical reactions.
• Reactants and products
• Free energy is the amount of energy available to
  perform work.
• Exergonic Reactions - Reactants have more free
  energy than products.
• Endergonic Reactions - Products have more free
  energy than reactants.

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ATP

• Adenosine triphosphate (ATP) is constantly being
  generated from Adenosine diphosphate (ADP).
• Composed of adenine and ribose (adenosine) and
  three phosphate groups.

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ATP Cycle
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Coupled Reactions

• In coupled reactions, the energy released by an
  exergonic reaction drives an endergonic reaction.

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Coupled Reactions
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Function of ATP

• Chemical Work - Energy needed to synthesize
  macromolecules.
• Transport Work - Energy needed to pump substances
  across plasma membrane.
• Mechanical Work - Energy needed to contract
  muscles, beat flagella, etc.

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Metabolic Pathways

• Reactions are usually part of a series of linked
  reactions.
• Begin with a particular reactant and terminate
  with an end product.
• Enzymes are protein molecules that function as
  organic catalysts to speed a chemical reaction.

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Energy of Activation

• The energy that must be added to cause molecules
  to react with one another is called the energy of
  activation.
• Enzymes lower energy of activation by bringing
  the substrates into contact with one another.

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Energy of Activation
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Enzyme-Substrate Complex
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Enzyme-Substrate Complex

• In most instances, only the active site complexes
  with the substrates.
• Active site undergoes a change in shape to
  accommodate the substrates.
• Induced fit model

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Enzyme Speed

• Generally, enzyme activity increases as substrate
  concentration increases.
• More collisions between substrate molecules and
  the enzyme.
• As temperature rises, enzyme activity increases.
• Warmer temperatures cause more effective
  collisions between enzyme and substrate.

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Enzyme Speed

• If temperature rises beyond a certain point, the
  enzyme becomes denatured and the enzyme activity
  levels out.
• Enzymes also have an optimal pH.

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Enzyme Concentration

• Cells regulate which enzymes are present and/or
  active.
• Enzyme Cofactors
• Vitamins
• Phosphorylation
• Enzyme Inhibition
• Feedback Inhibition

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Feedback Inhibition
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Feedback Inhibition

• Most metabolic pathways are regulated by another
  type of feedback inhibition.
• End product of the pathway binds to an allosteric
  site.
• Binding shuts down the pathway, and no more
  product is produced.

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Oxidation-Reduction

• In redox reactions, electrons pass from one
  molecule to another.
• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• Oxidation and reduction always take place at the
  same time as one molecule accepts the electrons
  given up by another molecule.

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Photosynthesis

• Carbon dioxide water solar energy yields
  glucose and oxygen.
• 6 CO2 6 H2O energy ? C6H12O6 6 O2
• Chloroplasts capture solar energy and convert it
  via electron transport chain to ATP.
• Coenzyme active during photosynthesis.
• NADP 2e- H ? NADPH

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Cellular Respiration

• Glucose oxygen yields carbon dioxide water
  energy.
• C6H12O6 6 O2 ? 6 CO2 6 H2O energy
• Most oxidations involve a coenzyme
• NAD 2e- H ? NADH

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Electron Transport System

• A series of membrane-bound carriers that pass
  electrons from one carrier to another.
• High-energy electrons delivered, and low-energy
  electrons leave.

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ATP Production

• Chemiosmosis Production of ATP due to a hydrogen
  ion gradient across a membrane.

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Review

• Forms of Energy
• Laws of Thermodynamics
• Metabolic Reactions
• ATP
• Metabolic Pathways
• Energy of Activation
• Enzymes
• Photosynthesis
• Cellular Respiration

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