Transcript Lab Exercise 39 - PCC - Portland Community College

Lab Activity 30
Digestive Enzymes
Portland Community College
BI 233
Cellular Reactions
• All molecules have energy barriers to prevent
spontaneous breakdown
• Enzymes speed up the cell’s 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)
• For a reaction to
occur, an energy
barrier must be
overcome
• Enzymes make the
energy barrier
smaller
EA
without
enzyme
starting
substance
EA with
enzyme
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
NORMAL BINDING OF SUBSTRATE
Substrate
Active
site
• A competitive
inhibitor takes
Enzyme
the place of a
substrate in the
Nonactive site
Competitive
competitive
• A noncompetitive inhibitor
inhibitor
inhibitor alters an
enzyme’s function
by changing its shape
ENZYME
INHIBITION
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Condensation
(aka Dehydration Synthesis)
• Two molecules combine
• Water is a byproduct
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2
1
3
2
3
4
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Hydrolysis
• Type of cleavage reaction
• Opposite of condensation
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1
2
2
3
4
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
Class
Monomer(s) Polymer(s)
Carbohydrates
monosaccharides
polysaccharides
Proteins
amino acids
polypeptides
Lipids
fatty acids
and glycerol
fats, steroids
phospholipids
Nucleic acids
nucleotides
polynucleotides
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Carbohydrate Digestion
•
Goal #1: Break complex carbs (starch)
down to oligosaccharides, trisaccharides,
disaccharides
1. Salivary Amylase: (minor): breaks complex
carbs (starch, glycogen) to oligosaccharides,
trisaccharides, and disaccharides. Inactivated by
gastric acid.
2. Pancreatic amylase: (major)
3. 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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Lugol’s IKI
• IKI: potassium iodide
• Indicator for starch
• Turns black in the presence of starch
IKI alone
Positive result
for starch
Negative result
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for starch
Benedict’s 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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Benedict’s
Solution
Before heating
After heating
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Protein Digestion
• Goal #1: Break Proteins down into smaller
polypeptides
• Pepsin (pepsinogen from stomach’s 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
1. Brush-border membrane
peptidases
2. Brush-border membrane
amino acid transporters
3. Brush-border membrane diand tripeptides transporters
4. Intracellular peptidases
5. Basolateral-membrane amino
acid carriers
6. 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 can’t
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
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