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Biology 102
Lab 12
Digestive System Enzymes:
Activity, Purpose, and Optimal
Conditions
1
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
2
Enzymes and Metabolic Reactions
Enzymes 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
3
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?
4
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?
IKI – Potassium Iodide
Benedict’s Reagent
What is an experimental control? What kinds of controls are there?
5
Enzymes used in today’s experiment
2. 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?
BAPNA - Nα-Benzoyl-DLarginine 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.
6
Enzymes used in today’s experiment
3. 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?
Example of using phenol red
as a pH change indicator
Is there anything else
we can use in the lab to
detect pH changes?
Acidic
(below 6.8)
Basic
(above 8.2)
7
Using PhysioEx 9.1
PhysioEX 9.1 is current
8
Using PhysioEx 9.1
Note: PhysioEx 9.1
is most current
version
9
Using PhysioEx 9.1
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Using PhysioEx 9.1
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Using PhysioEx 9.1
12
Using PhysioEx 9.1
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Using PhysioEx 9.1
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Using PhysioEx 9.1
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’.
15
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.
16
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
17
Amylase activity on Starch
18
Amylase activity on cellulose
19
Pepsin activity on BAPNA (protein)
20
Lipase activity on triglycerides
21