1. Portland Community College
Lab Activity 30
Digestive Enzymes
Portland Community College
BI 233

2. 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

3. Energy of Activation (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

4. 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

5. Enzymes Environmental conditions affect enzymes: Temperature pH
Salt concentration
When you “denature” an enzyme, you change its shape

6. 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

7. NORMAL BINDING OF SUBSTRATE
Enzyme Inhibitors
Inhibitors block enzyme action
A competitive inhibitor takes the place of a substrate in the active site
A noncompetitive inhibitor alters an enzyme’s function by changing its shape
NORMAL BINDING OF SUBSTRATE
Substrate
Active site
Enzyme
Non-competitive inhibitor
Competitive inhibitor
ENZYME INHIBITION

8. Condensation (aka Dehydration Synthesis)
Two molecules combine
Water is a byproduct 1 2 3 1 2 3 4

9. Hydrolysis Type of cleavage reaction Opposite of condensation 1 2 3 4

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

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

12. 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

13. 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

14. Lugol’s IKI IKI: potassium iodide Indicator for starch
Turns black in the presence of starch
IKI alone
Positive result for starch
Negative result for starch

15. 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)

16. Benedict’s Solution
Before heating
After heating

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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%),
Milk-derived lipase: in breast milk
Digestion products: fatty acids and glycerol

23. 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

24. The End
The End