Enzymes

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Enzymes

• Chapter 6
• Biology Campbell Reece

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What are enzymes?

• Catalyst a chemical agent that speeds up a
  reaction without being used up
• Can be used over and over again
• Enzyme a protein that is a catalyst
• Enzyme names usually end in ase
• Ex. Sucrase (breaks down sucrose)
• Amylase (breaks down amylose)
• DNA Polymerase (makes a copy of DNA)

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Pectinase

• An enzyme used in the food industry to increase
  fruit juice production
• Enzyme breaks down the polysaccharides in the
  cell walls of fruit to increase the juice
  extraction.
• Increases the volume of juice extracted

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Activation Energy

• A.K.A free energy of activation (EA)
• Usually comes in the form of heat
• Initial investment of energy for starting a
  reaction
• The reactants must be energized or activated in
  order to break and reform bonds

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Activation Energy

• Is this reaction endergonic or exergonic?
• Exergonic-releases energy
• Endergonic-absorbs energy

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How Enzymes Lower the EA Barrier

• An enzyme lowers the EA barrier
• It hastens reactions that would occur anyway

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Enzyme-Substrate Complex

• Substrate the reactant(s) an enzyme acts on
• Enzymes only bind to their specific substrate
• The enzyme binds to its substrate(s) at the
  active site to form the enzyme-substrate complex
• The substrate fits the active site
• The enzyme changes shape slightly to fit around
  the substrate more snugly (induced fit)

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Enzyme-Substrate Complex
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Enzyme-Substrate Complex
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How Enzymes Work

• Enzyme binds to the substrate at the active site
• Weak interactions (hydrogen or ionic bonds) hold
  the substrate in
• Side chains (R groups) of the amino acids in the
  active site catalyze the conversion of substrate
  to product(s)
• The product(s) depart the active site
• The enzyme is now free to bind to another
  substrate

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Factors That Affect Enzymes

• ? temperature, ? rate of enzymatic reaction (to a
  point)
• Each enzyme has an optimal temperature at which
  it operates best
• Each enzyme has an optimal pH (usually between
  6-8)

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Cofactors and Enzyme Inhibitors

• Cofactors non-protein helpers (vitamins)
• If the cofactor is organic it is called a
  coenzyme
• Competitive inhibitors block the substrate from
  entering the active site
• Noncompetitive inhibitors bind to another part
  of the enzyme, therefore changing its shape
• Some toxins, poisons and antibiotics are
  irreversible inhibitors

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Enzyme Inhibitors