Digestion Lab

Experiment #1:
Carbohydrate Digestion
• Tube 1

Digestion Lab

– 3 ml water

• Tube 2
– 3 ml 0.2% amylase

• Tube 3
– 3 ml 0.2% amylase + 10 drops of
1.0M HCl

• Tube 4

1

2

4

3

– 3 ml 0.2% amylase
– place in hot water bath for 5 min

Experiment #1:
Carbohydrate Digestion
• Add 5.0 ml starch solution to each tube
• Incubate in 37°C bath for
1.5 hr
• Divide contents of each tube evenly into 2 tubes
– Lugol’s Test
– Benedict’s Test

Experiment #1:
Carbohydrate Digestion
• Lugol’s Test
– presence of starch

2

1

1

2

3

4

• add a few drops of Lugol's reagent (iodine)

4

3

1

2

3

4

Experiment #1:
Carbohydrate Digestion

blue = - (none) green = + (a little bit) yellow = ++ (some) orange = +++ (lots)

3

4

or

• Add egg white into each tube
• Tube 1

– presence of maltose

–
–
–
–

2

Experiment #2:
Protein Digestion

• Benedict’s Test
• add 5.0 ml of Benedict's reagent
• immerse in hot water bath for 2 min • rate the amt of maltose present

1

– if starch absent, transparent brown color
– if starch present, opaque black-blue color

– 10 drops of water + 5.0 ml pepsin

• Tube 2
– 10 drops of 1M HCl + 5.0 ml pepsin
1

2

3

4

• Tube 3
– 10 drops of 1M HCl + 5.0 ml pepsin
– place in ice bath

1

2

3

4

5

• Tube 4
– 10 drops of 1M HCl + 5.0 ml water

• Tube 5
– 10 drops of 1M NaOH + 5.0 ml pepsin

1

Experiment #2:
Protein Digestion

Experiment #3:
Fat Digestion
• add 3.0 ml of cream to each tube
• Tube 1

• Incubate tubes 1,2,4 and 5 at
37 C for 1.5 hours
• Observe any digestion of egg white – 5.0 ml water + few grains of bile salts

• Tube 2
– 5.0 ml pancreatin

• Tube 3 undigested – 5.0 ml pancreatin + few grains of bile salts digested

Experiment #3:
Fat Digestion
• Test pH of each solution w/ pH probe
– rinse probe w/ detergent after each test

• Place in 37°C bath
• Retest pH at 20, 40 and 60 min Enzymes
Protein Catalysts
• speed up the rate of chemical reactions
• are not permanently altered in the reactions
• do not change the nature of the reaction

Digestion
•

Physical and chemical break down nutrients into absorbable unit
1. Physical digestion (chewing, mixing)
2. Chemical digestion (enzyme catalyzed)
•
•
•

polysaccharides → monosaccharides proteins → amino acids fats → glycerol + fatty acids

Factors Affecting Enzyme
Activity
• Temperature
– ↑ Temp, ↑ kinetic energy,
↑ reaction rate
– high Temp changes structure of enzymes
• ↓’s enzyme function

2

Factors Affecting Enzyme
Activity
• pH
– 3D structure of enzymes changes at different pH
– optimal enzyme function at specific pH
– ↓ function at higher or lower pH’s

Oxidation-Reduction Reactions

Carbohydrate Digestion
• begins with salivary amylase (ptyalin)
• breaks starch (polysaccharide) into maltose (disaccharide)
• Simple sugars = reducing sugars
– Drive reduction reactions for other substances
– Become oxidized

Benedict’s Test

• oxidation reaction
– reaction in which a molecule loses e-s

• reduction reaction
– reaction in which a molecule gains e-s

• Example
– NADH → NAD+ = oxidation
– NAD+ → NADH = reduction
– O2 + 4H+ + 4e- → 2H2O = reduction

Protein Digestion
• Begins in the stomach
• Gastric Epithelial Cells
– Parietal Cells
• Secrete HCl

– Chief Cells
• Secrete Pepsinogen

• Low pH activates pepsinogen • Pepsinogen autocatalyzes self into pepsin
• Cleaves proteins

• Cu2+ + Maltose (reduced)
→ Cu+ + Maltose (oxidized)
• 4 Cu+ + O2 → Cu2O (orange color)

Protein Digestion
• Continues in small intestine
– chyme enters pyloric sphincter – intestine releases hormone
(secretin), that stimulates the release of pancreatic juices
– Chymotrypsin, trypsin, etc.

• Enzymes activated in intestine • Digest small polypeptides into amino acids

3

Fat Digestion
• Begins in stomach
• Most in small intestine
– (pancreatic and intestinal lipases)

• Fats are nonpolar!
• Digestion depends on the presence of bile from the gall bladder
– emulsification breaks up fat into small droplets

• lipases break triglycerides into monoglycerides + fatty acids
• form micelles in intestinal lumen

Fat Digestion
• absorbed by the epithelium
• reform triglycerides in the epithelial cells
• combined w/ protein to form chylomicrons which are secreted into lacteals
• carried via lymph to the veins

Fat Digestion
• Triglycerides → glycerol + fatty acids
• Fatty acids lower pH of aqueous solutions
– ↑ fat digestion, ↓pH

4