Lab Activity 30

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Lab Activity 30

• Digestive Enzymes

Portland Community College BI 233
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Cellular Reactions

• All molecules have energy barriers to prevent
  spontaneous breakdown
• Enzymes speed up the cells chemical reactions by
  lowering energy barriers
• The amount of energy needed to overcome the
  energy barrier is the energy of activation (EA)
• Enzymes lower the EA for chemical reactions to
  begin decreases the amount of energy the
  reactants must absorb

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Energy of Activation (EA)
EA without enzyme

• For a reaction to occur, an energy barrier must
  be overcome
• Enzymes make the energy barrier smaller

EA with enzyme
starting substance
energy released by the reaction
products
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Enzymes

• A protein that acts as biological catalysts by
  lowering the activation energy
• Increase the rate of chemical reactions
• Are highly specific, they only act on one
  substrate or reaction
• Not consumed in the reaction
• E S ??ES complex ?? E P
• If there is no enzyme, the reaction will still
  happen, eventually Enzymes cannot make a
  non-spontaneous reaction spontaneous

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Enzymes

• Environmental conditions affect enzymes
• Temperature
• pH
• Salt concentration
• When you denature an enzyme, you change its
  shape

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Enzyme Helpers

• Some enzymes require non-protein cofactors
• Some are inorganic metal ions of zinc, iron, and
  other trace elements
• Some are organic molecules called coenzymes
• Includes vitamins or altered vitamin components

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Enzyme Inhibitors

• Inhibitors block enzyme action
• A competitive inhibitor takes the place of a
  substrate in the active site
• A noncompetitive inhibitor alters an enzymes
  function by changing its shape

NORMAL BINDING OF SUBSTRATE
Substrate
Active site
Enzyme
Non-competitiveinhibitor
Competitiveinhibitor
ENZYME INHIBITION
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Condensation (aka Dehydration Synthesis)

• Two molecules combine
• Water is a byproduct

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3
2
4
3
2
1
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Hydrolysis

• Type of cleavage reaction
• Opposite of condensation

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2
3
4
2
1
3
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Chemical Digestion

• Most digestive enzymes catalyze hydrolysis
  reactions.
• Addition of H2O breaks polymers into smaller
  subunits (monomers, dimers ect..)

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Four types of Macromolecules
Monomer(s)
Polymer(s)
Class
Carbohydrates
monosaccharides
polysaccharides
Proteins
amino acids
polypeptides
fats, steroids phospholipids
fatty acids and glycerol
Lipids
Nucleic acids
nucleotides
polynucleotides
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Carbohydrate Digestion

• Goal 1 Break complex carbs (starch) down to
  oligosaccharides, trisaccharides, disaccharides
• Salivary Amylase (minor) breaks complex carbs
  (starch, glycogen) to oligosaccharides,
  trisaccharides, and disaccharides. Inactivated by
  gastric acid.
• Pancreatic amylase (major)
• Amylase in breast milk

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Carbohydrate Digestion

• Goal 2 further breakdown into monosaccharides
• Use brush border enzymes on microvilli of small
  intestine
• 1. Lactase breaks lactose into glucose
  galactose
• 2. Maltase breaks maltose into 2 glucoses, (also
  works on oligosaccharides)
• 3. Sucrase breaks sucrose into glucose fructose

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Lugols IKI

• IKI potassium iodide
• Indicator for starch
• Turns black in the presence of starch

Positive result for starch
Negative result for starch
IKI alone
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Benedicts Solution

• Benedict's solution is used to detect the sugars
  glucose or maltose
• It is a blue solution that will turn red-orange
  (brick red) when heated in the presence of
  glucose or maltose
• (note that a sucrose solution would not change
  color)

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Benedicts Solution
Before heating
After heating
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Protein Digestion

• Goal 1 Break Proteins down into smaller
  polypeptides
• Pepsin (pepsinogen from stomachs chief cells)
• HCL in stomach denatures the proteins to enhance
  digestion.
• Pancreatic enzymes trypsin, elastase,
  chymotrypsin carboxypeptidase break large
  polypeptides to small polypeptides peptides

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Protein Digestion

• Goal 2 break polypeptides amino acids.
• On brush border peptidases
• Inside cytoplasm of intestinal cells several
  dipeptidases, tripeptidase break absorbed
  dipeptides and tripeptides into amino acids

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Protein Digestion

• Brush-border membrane peptidases
• Brush-border membrane amino acid transporters
• Brush-border membrane di- and tripeptides
  transporters
• Intracellular peptidases
• Basolateral-membrane amino acid carriers
• Basolateral membrane di- and tripeptides carriers

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Protein Digestion

• BAPNA is a dye attached to an amino acid via a
  peptide bond.
• Peptide bonds are bonds that link amino acids in
  polypeptides.
• When the peptide bond is broken in BAPNA with
  trypsin, the dye is released and turns yellow

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Fat Digestion

• Goal 1 Break Big fat droplets into smaller
  droplets
• Bile salts emulsify
• Smaller spheres of fat have higher surface/volume
• Makes lipase (water soluble enzyme that cant
  penetrate fat droplet) more efficient

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Fat Digestion

• Goal 2 Break triglycerides into monoglycerides
  and fatty acids
• Gastric Lipase from chief cells in fundus of
  stomach (20 of digestion)
• Digestion products monoglycerides and fatty
  acids
• Pancreatic Lipase (80),
• Digestion products monoglycerides and fatty
  acids
• Milk-derived lipase in breast milk
• Digestion products fatty acids and glycerol

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Litmus Cream

• Litmus is a pH indicator- purple in storage
  bottle
• It comes mixed with cream (a triglyceride source)
• Triglyceride digestion by lipase releases fatty
  acids.
• These fatty acids drop the pH, and litmus turns
  PINK

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The End
The End