digestion = hydrolysis reactions involving enzymes (enzymes = biological catalysts) -a specific...
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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”
BIO132 Lab 7: Exercise 39A/39 Chemical Processes of Digestion
Cofactor
Starch digestion by amylase (amylase)(amylase)
Starch (amylose) + water -------------------------> maltoseStarch (amylose) + water -------------------------> maltoseAssay 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)
Figure 39A.1 / 39.1
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 (pancreatic lipase)(pancreatic lipase)
Triglycerides + water ---------------------------> glycerol + fatty acidsTriglycerides + 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)
Figure 39A.1 / 39.1
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.
Additives(3 gtt ea)
1A 2A 3A 4A
Boil amylase4 min, thenadd starch
5A 6A
0C37C37C37C37C37CIncubationcondition
IKI test(color change)
Positive () ornegative ()result
Benedict’stest(color change)
Positive () ornegative ()result
Additive key:
Amylase Starch Maltose Water
Add acid
Salivary Amylase Digestion of Starch
Tube no.
Additives(3 gtt ea)
1A 2A 3A 4A
Boil amylase4 min, thenadd starch
5A 6A
0C37C37C37C37C37CIncubationcondition
IKI test(color change)
Positive () ornegative ()result
Benedict’stest(color change)
Positive () ornegative ()result
Additive key:
Amylase Starch Maltose Water
black
+
-
blue
yellow
-
-
blue
yellow
-
+
orange
black
+
-
blue
yellow
-
+
orange
dark
partial +
yellowish
partial +
Add acid
Unnumbered Figure 39.3
Pancreatic Lipase Digestion of Fats
Tube no.
37C
Positive () ornegative ()result
Additive key:
Lipase
1L
Boil lipase4 min, thenadd litmuscream.
2L 3L 4L 5L 4B 5B
37C 37C 37C 37C0C 0C
Color change
Incubationcondition
Additives(5 gtt ea)
Litmus cream Water Pinch bile salts
15
Pancreatic Lipase Digestion of Fats
Tube no.
37C
Positive () ornegative ()result
Additive key:
Lipase
1L
Boil lipase4 min, thenadd litmuscream.
2L 3L 4L 5L 4B 5B
37C 37C 37C 37C0C 0C
Color change
Incubationcondition
Additives(5 gtt ea)
Litmus cream Water Pinch bile salts
15
bluishpurple
bluish purple pink
- ++- -
purplebright pink
pinkishpurple
+++ +-/+
bluishpurple