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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
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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) Figure 39A.1 / 39.1
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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!
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Lipid digestion by lipase (pancreatic lipase) (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) Figure 39A.1 / 39.1
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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
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Salivary Amylase Digestion of Starch Tube no. Additives (3 gtt ea) 1A2A3A4A Boil amylase 4 min, then add starch 5A6A 0C0C37 C Incubation condition IKI test (color change) Positive ( ) or negative ( ) result Benedict’s test (color change) Positive ( ) or negative ( ) result Additive key: Amylase Starch Maltose Water Add acid
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Salivary Amylase Digestion of Starch Tube no. Additives (3 gtt ea) 1A2A3A4A Boil amylase 4 min, then add starch 5A6A 0C0C37 C Incubation condition IKI test (color change) Positive ( ) or negative ( ) result Benedict’s test (color change) Positive ( ) or negative ( ) result Additive key: Amylase Starch Maltose Water black + - blue yellow - - blue yellow - + orange black + - blue yellow - + orange dark partial + yellowish partial + Add acid
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Unnumbered Figure 39.3 Pancreatic Lipase Digestion of Fats Tube no. 37 C Positive ( ) or negative ( ) result Additive key: Lipase 1L Boil lipase 4 min, then add litmus cream. 2L 3L 4L 5L 4B 5B 37 C 0C0C0C0C Color change Incubation condition Additives (5 gtt ea) Litmus cream Water Pinch bile salts 15
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Pancreatic Lipase Digestion of Fats Tube no. 37 C Positive ( ) or negative ( ) result Additive key: Lipase 1L Boil lipase 4 min, then add litmus cream. 2L 3L 4L 5L 4B 5B 37 C 0C0C0C0C Color change Incubation condition Additives (5 gtt ea) Litmus cream Water Pinch bile salts 15 bluish purple bluish purple pink -++ - - purple bright pink pinkish purple +++ + -/+ bluish purple
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