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Biology 102
Lab 12 Digestive System Enzymes:
Activity, Purpose, and Optimal Conditions
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Objectives for Today
• Become more familiar with some of the enzymes used for chemical digestion
• For each enzyme used in today’s experiment, you should know:– Their major action, i.e., the type(s) of substrates on
which they act
– Their primary site of action in the body
– The optimal pH at which they work
– Additional factors, if any, they need to work efficiently
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Enzymes and Metabolic ReactionsEnzymes are Biological catalysts
• control rates of metabolic reactions• lower activation energy needed to start reactions• globular proteins with specific shapes• not consumed in chemical reactions• *substrate specific
• shape of active site (3D) determines which substrate(s) the enzyme can act on
Figure From: Marieb & Hoehn, Human Anatomy & Physiology, 9th ed., Pearson
Enzymes work optimally under specific conditions of temperature and pH
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Enzymes as Proteins – 3D Structure
Specific folding and bending of a polypeptide or protein.
**It is the 3-D structure of a protein that allows it to perform its specific function.
Secondary structure
Secondary structure
Figure from: Hole’s Human A&P, 12th edition, 2010
What would happen if an enzyme is exposed to extreme heat? pH?
Enzymes used in today’s experiment
1. Salivary amylase– Starch (polysaccharide) → Maltose (disaccharide)
– Salivary glands
– What do you predict is its optimum temp/pH?
– How would we know if this reaction has occurred?
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IKI – Potassium Iodide Benedict’s Reagent
What is an experimental control? What kinds of controls are there?
Enzymes used in today’s experiment2. Pepsin
– Proteins → Peptides, amino acids
– Where is pepsin active in the body? What does it do?
– What do you predict is its optimum temp/pH?
– How would we know if this reaction has occurred?
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BAPNA - Nα-Benzoyl-DL-arginine 4-nitroanilide hydrochloride
(the amino acid, arginine)
Causes solution to turn yellow when cleaved from BAPA by a peptidase
Yellow dye produced by the reaction changes the solution’s optical density; this can be measured by a spectrophotometer. Colorless solutions have an optical density of zero.
Enzymes used in today’s experiment3. Lipase
– Triglycerides → Monoglyceride + 2 Fatty acids
– Where do lipases come from in the body?
– What do you predict is their optimum temp/pH?
– Is there anything else lipases need to function efficiently in the body, e.g., in the intestine?
– How would we know if this reaction has occurred?
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Example of using phenol red as a pH change indicator
Is there anything else we can use in the lab to detect pH changes?
Basic(above 8.2)
Acidic(below 6.8)
Using PhysioEx 9.1
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PhysioEX 9.1 is current
Using PhysioEx 9.1
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Note: PhysioEx 9.1 is most current version
Using PhysioEx 9.1
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Using PhysioEx 9.1
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Using PhysioEx 9.1
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Using PhysioEx 9.1
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Using PhysioEx 9.1
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Using PhysioEx 9.1
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Note: Save this to the desktop and name the file: Lab12_<Day>_Group<#>.pdf
Email me the file ([email protected]), and be sure to email one to yourself and the other members of your group if you want a copy for studying.
Put the names of your group members in the subject line of the email followed by ‘Lab 12’.
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What You Should Do in Lab Today…• Using the DVD version or online version of the
software, access PhysioEx 9.1 in Mastering A&P and do Exercise 8:– Salivary amylase (Activities 1 and 2)
– Pepsin (Activity 3)
– Lipase (Activity 4)
• For each experiment, – Be sure to do the pretest
– Answer the ‘Prediction’ questions as you go
– Generate a PDF file to submit as your lab report (so, you will be submitting 4 PDF files)
• Also submit a Summary Table Lab Report (hard copy) from your group.
For next lab…
• Gross/microscopic anatomy of the urinary system– Human models– Cats
• Gross anatomy of the reproductive system– Human models (no, not live ones!)– Cats
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Amylase activity on Starch
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Amylase activity on cellulose
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Pepsin activity on BAPNA (protein)
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Lipase activity on triglycerides
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