Metabolism: Energy and Enzymes

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Metabolism Energy and Enzymes

• Chapter 6

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Energy

• Energy the ability to do work or bring about
  change
• Living things constantly change and perform
  metabolic reaction to develop, grow, and reproduce

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Forms of energy

• Kinetic energy energy of motion
• Mechanical energy application of kinetic energy
• Potential energy stored energy
• Chemical energy energy in found organic
  molecules

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Flow of Energy
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Laws of Thermodynamics

• First Law Law of Conservation of Energy
• Energy cannot be created or destroyed, but it can
  be changed from one form to another
• Plants use solar energy to make carbohydrates
  from CO2 and H2O
• Energy is not destroyed in reactions but rather
  transferred to heat energy

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Laws of Thermodynamics

• Second Law Law of Entropy
• Energy cannot be changed from one form to another
  without the loss of usable energy
• Energy can be lost as heat when heat dissipates,
  it is no longer usable energy
• Every energy transformation makes the universe
  less organized and more disordered (increases
  entropy)

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Metabolism

• Metabolism sum of all the chemical reaction
  that occur in a cell
• Reactants substances that react
• Products substances that are formed

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Free Energy

• Free energy (G) amount of energy available
  after a reaction has occurred
• ?G change in free energy
• ?G(G of products) (G of reactants)
• Exergonic reactions - Products have less free
  energy than reactants
• Endergonic reactions - Products have more free
  energy than reactants

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Exergonic Reaction

• Exergonic Reaction chemical reaction that
  releases energy
• Negative free energy
• -?G G of reactants is greater than G of
  products
• Reaction will proceed spontaneously without input
  of energy
• Free energy released as reaction proceeds

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Endergonic Reaction

• Endergonic Reaction chemical reaction that
  requires the input of energy
• Positive free energy
• ?G G of products is greater than that of
  reactants
• Needs energy input for reaction to proceed

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Coupled reactions

• In body exergonic reactions are often coupled
  with endergonic reactions
• The free energy released by the exergonic
  reaction can be used to drive the endergonic
  reaction

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ATP

• ATP Adenosine Triphosphate
• Used as energy to fuel reactions
• Produced when needed from adenosine diphosphate
  (ADP) and inorganic phosphate ?

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Structure of ATP

• Composed of adenine, ribose and 3 phosphate
  groups
• 3rd PO4 group is easily removed with the release
  of 7.3 kcal per mole

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ATP Cycling
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Coupled Reactions
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Function of ATP

• Chemical work supplies energy needed to
  synthesize macromolecules
• Transport work supplies energy needed to pump
  substances across the plasma membrane
• Mechanical work supplies energy needed to
  contract muscle, beat flagella, etc.

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Metabolic Pathways

• Reactions are usually part of a series of linked
  reactions Metabolic pathways
• Products of earlier reactions become the
  reactants for later reactions
• Begin with a particular reactant, proceeds
  through several intermediates, and terminate with
  an end product
• A ? B ? C ? D ? E

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Enzymes

• Enzymes proteins that function as organic
  catalysts to speed a chemical reaction
• Substrates reactants in enzymatic reactions
• Each enzyme accelerates a specific reaction
• Each reaction in a metabolic pathway requires a
  unique and specific enzyme
• End product will not appear unless ALL enzymes
  present and functional

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Energy of Activation

• Energy of activation the energy that must be
  added to cause molecules to react with one
  another
• 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

• 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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Degradation vs. Synthesis

• Degradation
• Enzyme complexes with a single substrate molecule
• Substrate is broken apart into two product
  molecules
• Synthesis
• Enzyme complexes with two substrate molecules
• Substrates are joined together and released as
  single product molecule

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Enzyme-Substrate Complex
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Enzyme Speed

• Substrate concentration
• Generally, enzyme activity increases as substrate
  concentration increases
• More collisions between substrate molecules and
  the enzyme

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Enzyme Speed

• Temperature
• As temperature rises, enzyme activity increases
• Warmer temperatures cause more effective
  collisions between enzyme and substrate
• If temperature rises beyond a certain point, the
  enzyme becomes denatured and the enzyme activity
  levels out

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Temperature
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Enzyme Speed

• pH
• Enzymes also have an optimal pH

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Enzyme Concentration

• Amount of enzyme available can also limit the
  rate of an enzymatic reaction
• Cells regulate which enzymes are present and/or
  active
• Gene transcription

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Enzyme Cofactors

• Enzyme Cofactors inorganic or organic,
  non-protein molecules required by enzymes to be
  active
• Ions metal ions such as copper, zinc, and iron
• Coenzymes organic, non-protein cofactors

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Vitamins

• Vitamins small organic molecules that are
  required for synthesis of coenzymes
• Can become part of the coenzyme
• Nicotinamide adenine dinucleotide (NAD)
• Nicotinamide adenine dinucleotide phosphate (NADP)

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Phosphorylation

• Phosphorylation addition of phosphate groups to
  a molecule
• Can modify an enzyme to activate it
• Kinases

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Enzyme inhibition

• Enzyme inhibition when active enzyme is
  prevented from combining with its substrate
• Feedback inhibition used to regulate most
  enzymes in the cell
• Competitive product binds to active site of
  enzyme
• Allosteric product binds to a site on the
  enzyme other than the active site and inhibits
  activity

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Feedback Inhibition
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Irreversible Enzyme Inhibition

• Materials that irreversibly inhibit an enzyme are
  known as poisons
• Cyanides inhibit enzymes resulting in all ATP
  production
• Penicillin inhibits an enzyme unique to certain
  bacteria
• Heavy metals irreversibly bind with many enzymes
• Nerve gas irreversibly inhibits enzymes required
  by nervous system

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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 in
  mitochondria and chloroplasts that pass electrons
  from one carrier to another
• Arranged in ordered series
• High-energy electrons delivered, and low-energy
  electrons leave

• Pass electrons from one carrier to another
• Electron energy used to pump hydrogen ions (H)
  to one side of membrane
• Establishes electrical gradient across membrane
• Electrical gradient used to make ATP from ADP
  Chemiosmosis
• Ends with low-energy electrons and high-energy
  ATP

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ATP Production

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

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