BIO132 Lab 7:
Exercise 39A/39 Chemical Processes of Digestion
Digestion = hydrolysis reactions involving enzymes
(enzymes = biological catalysts)
-a specific enzyme acts on a specific substrate using water to break
chemical bonds resulting in particular products
-the specificity is based on the active site of the enzyme; a space in
folded protein structure where the substrate will fit and bind
-enzymes are usually named for their substrate and end in “-ase”
Cofactor
Figure 39A.1 / 39.1
Starch digestion by amylase
(amylase)
Starch (amylose) + water -------------------------> maltose
Assay for enzyme (amylase) activity:
Assay for starch:
Lugol’s IKI + starch = blue/purple/black precipitate
Assay for maltose:
Benedict’s reagent + maltose = green, yellow, orange, red
precipitate (green = less maltose, red = more)
Lipid emulsification by bile
(mix)
Fats and oils + bile --------------------------> emulsified fats
(tiny droplets suspended in water)
allows easier access by water-soluble enzymes
*NOT digestion!
Lipid digestion by lipase
Figure 39A.1 / 39.1
(pancreatic lipase)
Triglycerides + water ---------------------------> glycerol + fatty acids
Assay for enzyme (lipase) activity:
Litmus cream = milk cream (triglycerides) + litmus pH indicator
Neutral to alkaline pH litmus is purple to blue (cream is neutral)
Acidic pH litmus is pink (assay for fatty acids which have acid pH)
Enzymes are biological catalysts, proteins that function to “speed up”
chemical reactions by holding substrate in the active site.
Enzymatic reactions can be impacted by environmental conditions:
-Enzymes have optimal temperatures and pH for their activity.
-Human digestive enzymes have an optimal temperature equal to body
temperature (37°C). Most have an optimal pH around neutral
(pH7)
-If the temperature is too high, or pH is too acidic or basic, enzymes can
be denatured and will no longer catalyze the reaction.
-If the temperature is too low, enzymes will function slowly or not at all
in the reaction.
native conformation
denatured
Salivary Amylase Digestion of Starch
Tube no.
1A
2A
3A
4A
37C
0C
Add acid
37C
37C
37C
37C
IKI test
(color change)
Positive () or
negative ()
result
Benedict’s
test
(color change)
Positive () or
negative ()
result
Additive key:
 Amylase
6A
Boil amylase
4 min, then
add starch
Additives
(3 gtt ea)
Incubation
condition
5A
 Starch
 Maltose
 Water
Salivary Amylase Digestion of Starch
Tube no.
1A
2A
3A
4A
37C
0C
Add acid
Incubation
condition
37C
IKI test
(color change)
yellow black yellow
37C
37C
37C
black
yellow
-
-
+
-
+
Benedict’s
test
(color change)
blue
blue
orange
blue
Positive () or
negative ()
result
-
-
+
-
Additive key:
 Amylase
6A
Boil amylase
4 min, then
add starch
Additives
(3 gtt ea)
Positive () or
negative ()
result
5A
 Starch
 Maltose
 Water
dark
partial +
orange yellowish
+
partial +
Unnumbered Figure 39.3
Pancreatic Lipase Digestion of Fats
Tube no.
1L
2L
3L
4L
5L
4B
5B
37C
0C
37C
0C
Boil lipase
Additives
(5 gtt ea)
4 min, then
15
add litmus
cream.
Incubation
condition
37C
37C
37C
Color change
Positive () or
negative ()
result
Additive key:
 Lipase
 Litmus cream
 Water
 Pinch bile salts
Pancreatic Lipase Digestion of Fats
Tube no.
1L
3L
2L
4L
5L
4B
5B
37C
0C
37C
0C
Boil lipase
Additives
(5 gtt ea)
4 min, then
15
add litmus
cream.
Incubation
condition
37C
Color change
Positive () or
negative ()
result
37C
37C
bluish bluish
purple purple
-
bluish purple
-
-
Additive key:
 Lipase
 Litmus cream
 Water
 Pinch bile salts
bright pinkish
purple
pink
pink purple
++ -/+ +++ +