Drosophila Genetics Simulation

Publication No. 10998
Drosophila Genetics Simulation
Introduction
Explore how the appearance of an organism relates to its genetic makeup using this interactive Drosophila Genetics card
simulation. Simulate a monohybrid genetic cross between wild-type and sepia fruit flies.
Concepts
• Genotype vs. phenotype
• Monohybrid cross
Background
Genetics is the scientific study of heredity. Scientists substitute simple organisms for humans when studying inherited diseases and disorders. About 60% of the genes that are known to cause human disease have a recognizable match in the genetic
code of the common fruit fly (Drosophila melanogaster), and 50% of Drosophila’s protein sequences are similar to those of mammals. Fruit flies are commonly used in genetic research because these gene and protein similarities are contained in an organism
with only four pairs of chromosomes—the X/Y sex chromosomes and three autosomes, numbered 2, 3 and 4. The four pairs of
chromosomes contain 132 million base pairs of DNA, comprising 13,676 genes. For comparison, the human genome has 3.2 billion base pairs, which make up 20,500 genes on 23 chromosomes. Other advantages to using Drosophila are that they breed and
mature rapidly, are inexpensive and easy to raise, produce several hundred offspring per generation, and require very little space.
The fruit fly is also an ideal candidate for genetic studies because simple mutations cause obvious phenotype (the outward appearance of an organism) differences, and its genome map has been fully sequenced (completed in 2000).
Genes are sections of a chromosome that code for individual proteins. A trait is defined as a physical characteristic that can
be passed from parent to offspring. Alternate forms of a gene are called alleles. Most organisms have two copies of every gene,
one inherited on the chromosome from the mother and one on the chromosome inherited from the father. Individuals carrying two
identical versions or alleles of a given gene, which may be either AA or aa, are said to be homozygous for the gene. Similarly,
when two different alleles are present in a gene pair, labeled Aa, the individual is said to have a heterozygous genotype. The
homozygous dominant genotype (AA) and the heterozygous genotype (Aa) will both show dominant phenotypes (because A is
dominant to a) whereas the homozygous recessive genotype (aa) will exhibit a recessive phenotype. These rules apply not only for
a single characteristic or traits resulting from a monohybrid cross, but also for a dihybrid cross in which two genes associated with
different traits with contrasting characteristics are considered. A special case exists for genes on the sex chromosomes. Since the Y
chromosome contains very few genes, the only copy of a gene in a male resides on the X chromosome which may cause a recessive gene to be expressed even though there is only one copy of the gene present. Sex-linked inheritance occurs mostly in males
because a female has two copies of the X chromosome and therefore her genotype will follow normal inheritance rules.
Drosophila Characterization
Like all insects, Drosophila have three main body parts: the head, the thorax, and the abdomen (see Figure 1). The major structures on the head of a wild-type fruit fly are the large red
compound eyes. There are also two antennae on top of the fly’s head used for smelling. The
mouth is a proboscis—the fly lowers it to suck up food like a vacuum cleaner. The thorax has
six legs, two wings and, on the dorsal (top) side, a number of long dark bristles. Females have
stripes on every segment of their abdomen. Males have shorter abdomens, and the last few segments of the abdomen are solid black. Males also have a set of brown anal plates on the ventral
(bottom) side of the abdomen (see Figure 2 on page 2).
Figure 1. Drosophila
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Sexing Flies
In selecting flies for genetic mating, it is absolutely essential that the sex of each fly be properly identified. Identification of
sex is most reliably done by examination of the genital organs with the aid of magnification, using a stereoscope. The external
reproductive organs of both the male and the female are located on the ventral, posterior part of the abdomen (see Figure 2). The
male genitalia are surrounded by heavy, dark bristles that are not found on the female. This characteristic is quite distinct even in a
fly that has just emerged from the puparium. Female genitalia are seen as a small bump on the end of the abdomen. The posterior
part of the abdomen is quite dark in males and considerably lighter in females. The tip of the abdomen is also rounded in males
and more pointed in females. Male fruit flies tend to be smaller than females.
A. Male
Large
band at
end of
abdomen
Left Foreleg
Ventral
Dorsal
B. Female
Stripes
Dorsal
Left Foreleg
Ventral
Figure 2. Dorsal and Ventral View of Drosophila
With practice and care, the front legs can also be used to distinguish the sexes. There are sex combs on the front legs of the
male fly (used for grasping the female).
Drosophila Mutations
The wild-type fruit fly has full wings, red eyes, and brownish-tan coloring, along with bristles and antennae. There are many
trait mutations available for crossing. Most mutations involve a change in the eyes, wings, bristles or antennae. The changes may
be the complete absence of the feature, such as no eyes, a change in shape, such as bar-shaped eyes, or a change in color, such as
white eyes. Each mutant type is given a name suggesting the main distinguishing feature. The name is usually a descriptive adjective, such as “black,” or a noun, such as “bar.” For convenience in listing and labeling, a representative symbol is assigned to each
mutant type. By convention, if the trait is recessive it is listed as lowercase letter(s), while dominant traits are listed as uppercase
letter(s). Wild-type is designated by a plus sign (+). See Table 1 for a list of common trait mutations in Drosophila.
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© 2011 Flinn Scientific, Inc. All Rights Reserved.
10998
Table 1. Common Drosophila Mutations
Symbol
Dominant or
Recessive
Bar
B
Dominant
White
Yellow
Apterous
w
y
ap
Recessive
Recessive
Recessive
Black
b
Recessive
Dumpy
Lobe
Vestigial
Ebony
dp
L
vg
e
Recessive
Dominant
Recessive
Recessive
Sepia
se
Recessive
Trait
Description
Chromosome #
Eyes are restricted vertically to a narrow bar in males and in
homozygous females.
Eyes are a distinctive white in color.
Body color is yellow.
Wings are absent.
Black color on the ends of the legs, wing veins, and the body.
Pigmentation darkens with age.
Wings shortened 25%, to approximately the length of the body.
Eyes greatly reduced in size, with indentation at anterior edge.
Stumpy, underdeveloped wings.
Body color is shiny black.
Red-brown eyes at emergence darken to sepia and ultimately
to black as the fly ages.
X
X
X
2
2
2
2
2
3
3
Punnett Squares
Punnett squares will be used in this activity to determine the gene combinations that might result from Drosophila crossings.
A sample Punnett square for a monohybrid cross between a dumpy female (dp/dp) and a wild-type male (+/+) is shown in Figure
3 below. Notice how the gametes are individually represented in the Punnett square. In this cross, all of the resulting phenotypes
are wild-type flies.
P
dp/dp
+/+
Gametes
+
+
dp
dp/+
dp/+
dp
dp/+
dp/+
Figure 3.
In a dihybrid cross, two pairs of contrasting characteristics are compared simultaneously. For example, a heterozygous nonvestigal winged female with non-ebony body color (vg+/vg e+/e) is crossed with a heterozygous male with non-vestigal wings and
non-ebony body color (vg+/vg e+/e). In the dihybrid cross represented above, four possible gamete combinations (vg+e+, vg+e,
vge+, and vge) would be placed in a four-column by four-row Punnett square and crossed with one another to find the resulting
offspring.
Materials
Fruit Fly Genetics Card Deck
Monohybrid Cross Sheet
Safety Precautions
This classroom activity is considered nonhazardous. Follow all standard classroom safety guidelines.
Procedure
Part I. Monohybrid Cross
1. A monohybrid cross will be simulated as a wild type (+) male fly will be crossed with a virgin female sepia fly (se). The
genotype symbol for this parent (P) fly cross is written as se/se and +/+. The parent fly genotype symbols are already provided on the Monohybrid Cross Sheet.
2. The cards from the Fruit Fly Genetics Card Deck represent the phenotypes of the flies. Locate a female sepia Fruit Fly
Card and a male wild type Fruit Fly Card from the Fruit Fly Genetics Card deck. Use the information from the Background
section to help identify these cards.
3. Place these cards on the P squares of the Monohybrid Cross Sheet.
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© 2011 Flinn Scientific, Inc. All Rights Reserved.
10998
4. Record the corresponding gamete symbols in the Punnett square headers below the P generation. The gamete for each
header of the Punnett square is simply one-half of each parent’s genotype symbol. For example, the male wild type fly will
have a + in each of the top two empty gamete boxes.
5. Complete this cross by writing in the genotype for each gamete combination in the four squares below the parent cards.
The resulting genotype(s) represent the F1 generation.
6. Locate the corresponding Fruit Fly Cards for each F1 genotypes. The fruit fly cards may be male or female. Place the correct cards over each written genotypes for the F1 generation. Remember that the wild type gamete + is dominant. These
cards represent the F1 phenotypes.
7. Cross an F1 female (would be virgin in an actual cross) with an F1 male. Record the genotype symbols for each of these
flies next to the F1 Parents boxes.
8. Place a male Fruit Fly Card and female Fruit Fly Card from the F1 generation from step 7 on each of the F1 parent genotype symbols.
9. Record the corresponding gamete symbols in the Punnett square headers below F1 parent cards.
10. Complete this cross by writing in the genotype for each gamete combination in the four squares below the F1 parent cards.
The resulting genotype(s) represent the F2 generation.
11. Locate and place the correct Fruit Fly Cards for each of the resulting F2 genotypes. The fruit fly cards may be male or
female. Place the correct cards over the written genotypes for the F2 generation. These cards represent the F2 phenotypes.
Disposal
The cards used in this activity may be saved and stored for future use.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Evidence, models, and explanation
Constancy, change, and measurement
Content Standards: Grades 5–8
Content Standard A: Science as Inquiry
Content Standard C: Life Science, structure and function in living systems, reproduction and heredity, populations and
ecosystems, diversity and adaptations of organisms
Content Standards: Grades 9–12
Content Standard A: Science as Inquiry
Content Standard C: Life Science, the cell, molecular basis of heredity, biological evolution, interdependence of organisms; matter, energy, and organization in living systems
The Drosophila Genetics Simulation is available from Flinn Scientific, Inc.
Catalog No.
FB1912
Description
Drosophila Genetics Simulation
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
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© 2011 Flinn Scientific, Inc. All Rights Reserved.
10998
P
se / se
+/+
Gametes
M
O
N
O
H
Y
B
R
I
D
C
R
O
S
S
F1
Parents
Gametes
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© 2011 Flinn Scientific, Inc. All Rights Reserved.
10998
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© 2011 Flinn Scientific, Inc. All Rights Reserved.
10998
Publication No. 10882
Codon Bingo
Introduction
Codon Bingo is a stimulating game that involves deciphering the genetic code. The game is designed to give students practice
with transcription and translation of codons while at the same time generating full class participation. As students play the game,
they develop increased proficiency while unraveling the genetic code found in the base pairs. After playing Codon Bingo, the students will find it easier to transcribe the DNA base pair messages into mRNA codons and to translate the mRNA codons into an
amino acid sequence.
Concepts
• Amino acids
• Nucleotide (base) pairing rules
• Transcription
• DNA
• RNA
• Translation
Background
The DNA that makes up the human genome can be subdivided into genes. Each gene encodes for a protein (or part of a protein) that performs a specific function in a cell. The two-step process of transcription and translation is responsible for transforming the DNA instructions into a functional protein. During transcription the DNA code is copied into a strand of messenger RNA
(mRNA). The nucleotide pairing rules for transcribing DNA to RNA are slightly different than the base pairing rules for replicating a strand of DNA. In DNA, the purine adenine (A) always pairs with the pyrimidine thymine (T), and the pyrimidine cytosine
(C) always pairs with the purine guanine (G). In RNA, the pyrimidine cytosine (C) still pairs with the purine guanine (G), but the
purine adenine (A) pairs with the pyrimidine uracil (U). The strand of mRNA travels out to the cytoplasm of the cell. In the cytoplasm a ribosome binds to the mRNA strand at a specific point called a start codon. The ribosome reads three mRNA nucleotides
at a time—these base triplets are called codons.
A single mRNA nucleotide sequence—adenine-uracil-guanine (AUG)—acts as the starting point for the translation of any
mRNA into a chain of amino acids. There are three different codons that are read as “stop” by the ribosome, causing the ribosome
to detach from the mRNA strand. The remaining 61 of the 64 possible nucleotide combinations codons correspond to one of the
twenty amino acids used to form an amino acid chain that will become a protein. Each mRNA codon is matched to an anticodon
on a transfer RNA (tRNA) molecule. The tRNA molecule has two key areas that are important for translation. The first area is
the anticodon. The anticodon is a triplet base nucleotide sequence that mirrors and is complementary to the 64 codon sequences
found in mRNA. The second area on tRNA has a specific amino acid bonded to it. The codons are a universal code, meaning that
each mRNA codon codes for the same amino acid in all living things from bacteria to humans. It is the specific sequence of amino
acids that varies in different proteins. Changes in the amino acid sequence cause the amino acid string to bend and fold in unique
ways, creating unique proteins for each organism.
Materials
Amino Acid Decoding Chart
Index cards, 64
Bingo card, blank
Small cups to hold the bingo chips
Bingo chips, 25 per student
Procedure
1. Using index cards, create the bingo “draw cards” by writing the name of an amino acid, an mRNA codon for that amino
acid (or stop), and the DNA code that corresponds to the mRNA codon. Create one card for each of the 64 RNA codons.
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2. Create bingo cards using a word processing program. Bingo cards have five columns and five rows, creating twenty-five
empty boxes. If desired, a free-space may be added to the center box of each bingo card.
3. Have the students randomly write the name of all 20 amino acids plus stop on the bingo card. Five amino acids must be
used twice to fill the bingo card. Note: Students should not use methionine or tryptophan more than once as they only have
one RNA code.
4. Give an Amino Acid Decoding Chart and a small cup containing 25 bingo chips to each student.
5. Shuffle the bingo draw cards and begin the first game.
6. Draw one bingo draw card. Call out the mRNA codon. Students must use the Amino Acid Decoding Chart to translate the
mRNA codon into the amino acid. If the student’s bingo card has the amino acid, a bingo chip should be placed on that
box.
7. Lay the bingo draw card to one side. It will be used to check the winner’s bingo card. Give the students enough time—
especially in the beginning of the game—before drawing the next game piece.
8. Continue to call out mRNA codons until a student says “Bingo!” Check the winner’s bingo card against the bingo draw
cards. If the student has made a mistake continue to call out new mRNA codons; otherwise, have the students clear the
bingo cards and start a new game.
9. Advanced variation—rather than call out mRNA codons, call out the DNA bases. Students must first transcribe the DNA
to mRNA, and then translate the mRNA code to the amino acid.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Systems, order, and organization
Content Standards: Grades 5–8
Content Standard A: Science as Inquiry
Content Standard C: Life Science, reproduction and heredity
Content Standards: Grades 9–12
Content Standard A: Science as Inquiry
Content Standard C: Life Science, molecular basis of heredity
Tips
• Most student textbooks contain an amino acid decoding chart or table. Three versions are typically found in textbooks—
two versions are tables, whereas the third version is circular with the amino acids appearing as “spokes on a wheel.” Allow
students to use the type of chart they are likely to use during a test.
• Bingo may be called when any five spaces across are filled, either horizontally, vertically or diagonally. Four corners, postage stamp, or blackout are less traditional bingo choices. Play the game with as many or as few bingo variations as you
desire.
Acknowledgment
Special thanks to Cynthia Mannix for bringing this activity to our attention.
A Codon Bingo Kit is available from Flinn Scientific, Inc.
Catalog No.
FB1112
Description
Codon Bingo Kit
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
–2–
© 2011 Flinn Scientific, Inc. All Rights Reserved.
10882
Amino Acid Decoding Chart
mRNA
Phenylalanine
Glutamic Acid
Serine
Glycine
Aspartic Acid
Tyrosine
Gly
Alanine
Glu
Phe Leu
Ser
U C A G U C AG U
CA
C
G
Tyr
U
p)
Ala G
U
C (sto )
G U
A
A (stop
C
A
C
G
U
C
A
U Cys
G
C
Val A
A (stop)
C
G
U
G Trp
U
G
U
G
Arg A
U
C
C
A Leu
G
Ser U
C
A
G
U
A
C
C
A
Lys
C
A
U G
U
G Pro
G
U
Asn
A
C
CU
A
G
G A
His
C U G A CU
Thr
Asp
Valine
G
U
A
C
(sta
r
Cysteine
Tryptophan
Leucine
Proline
Gln
t)
Met
Lysine
AG
Ile
Arg
Asparagine
Histidine
Threonine
Isoleucine
Glutamine
Methionine
Arginine
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10882
© 2011, Flinn Scientific, Inc. All Rights Reserved. Reproduction permission is granted to science teachers who are current customers of Flinn Scientific, Inc. Batavia, Illinois, U.S.A. No part of this
material may be reproduced or transmitted in any form or by any means, electronic or mechanical, including, but not limited to photocopy, recording, or any information storage and retrieval system,
without permission in writing from Flinn Scientific, Inc.
© 2010 Flinn Scientific, Inc. All Rights Reserved.
10998A
Publication No. 11000
Germ Transmission
Introduction
Infections and parasitic diseases may be spread from person to person through air, water, and physical contact. Show students
how easily germs can spread and emphasize the importance of good hygiene using fluorescent lotion.
Concepts
• Disease control
• Fluorescence
• Disease prevention
• Proper hygiene
Background
Contagion, causal agent, and pathogen are broad terms used to describe any virus, bacteria, prion (protein), protozoa, worm
or genetic mutation that causes harm to living things. Most of these potential disease agents are invisible to the naked eye and also
fairly widespread—the majority of surfaces are covered with both beneficial and pathogenic microbes. The type and concentration of pathogenic microbes, combined with the health and immune capabilities of the human host, determine how, when and if
a person will get sick. The study of how and why people and animals become ill and how to prevent and control illness is called
epidemiology.
Epidemiologists define an infectious disease as any disease easily transmitted by contact between a host and a victim. Contact
can be direct between two individuals through kissing, hugging or shaking hands. Contact can also be indirect. In this case the contagion is transmitted by contact with an inanimate object that harbors the pathogen. These inanimate objects are called formites.
Toys, money, kitchen sponges, cups, toothbrushes, and pencils are just a few examples of formites. Formites become infected by
touch, through droplets created by coughing, sneezing, or talking, and also through airborne particles that float in the air for a long
time before eventually settling on the surface of various objects. Formites can be contagious for minutes or days, depending on the
contagion. Disinfecting formites frequently, avoiding the sharing of formites, cleaning hands after touching a formite, and staying
away from other people when they are (or you are) contagious are the best methods of controlling mild illnesses.
Glowing Germ lotion is a handy tool to demonstrate the spread of disease by physical contact. In incandescent light Glowing
Germ appears the same as regular hand lotion. However, in the presence of a black light it fluoresces. Fluorescence only occurs in
the presence of an exciting source. In this case the exciting source is an ultraviolet “black” light.
Energy Level Diagram
Excited
Electronic State
Energy
In fluorescence, when a light source is shined on a material,
a photon is absorbed. The energy from the photon is transferred
to an electron that makes a transition to an excited electronic
state. From this excited electronic state, the electron naturally
wants to relax back down to the ground state. When it relaxes
back down to the ground state, it emits a photon (symbolized by
the squiggly arrow in the diagram). This relaxation may occur in
a single step or in a series of steps. If it occurs in a single step,
the emitted photon will be the same wavelength as the exciting
photon. If the relaxation occurs in a series of steps emitting a
photon along the way, the emitted photon will have a greater
wavelength (lower energy) than the exciting photon.
If the emitted photon’s wavelength is in the visible portion
of the spectrum, we observe a colorful, glowing effect. Emission
of this form is termed fluorescence. This process is practically
instantaneous so the fluorescence is observed as soon as the
exciting source is present, and it disappears as soon as the exciting source is removed.
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Emitted Photon
Ground State
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081110
Materials
Glowing Germ fluorescent lotion
Nitrile gloves
Ultraviolet light source
Safety Precautions
Glowing Germ is a consumer product with minimal safety hazards. Any lotion may cause skin irritation to individuals with
extremely sensitive skin. Wear chemical splash goggles whenever chemicals, heat or glassware are used. Wash hands thoroughly with
soap and water before leaving the laboratory. Please review current Material Safety Data Sheets for additional safety information.
Procedure
1. Put on a clean pair of nitrile gloves.
2. Place Glowing Germ on the hands of one participant. Rub it over the gloves similar to hand lotion.
3. Each participant should shake hands with every other individual in the demonstration.
4. Turn off the lights so the room is dark.
5. Turn on an ultraviolet light and observe where the “germs” have spread.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and
review all federal, state and local regulations that may apply, before proceeding. Place the used gloves as well as the empty bottle
of Glowing Germ in the trash for solid waste disposal according to Flinn Suggested Disposal Method #26a.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Evidence, models, and explanation
Content Standards: Grades 5–8
Content Standard B: Physical Science, properties and changes of properties in matter, transfer of energy
Content Standard F: Science in Personal and Social Perspectives, personal health
Content Standards: Grades 9–12
Content Standard B: Physical Science, structure of atoms, structure and properties of matter, chemical reactions
Content Standard F: Science in Personal and Social Perspectives, personal and community health
Tips
• This demonstration may be done at the beginning of the school year to illustrate why eating or drinking in a lab setting
should not be allowed and why students should always wash their hands before leaving the lab.
• The demonstration is also highly relevant in biology courses to illustrate the spread of bacteria and microorganisms and
the importance of following sterile technique.
• An alternative procedure for this demonstration involves placing Glowing Germ on an object such as a door handle that
will frequently be touched by students. Regular lotion can be used in other locations so it is not as obvious where the
“germs” originated.
• Glowing Germ lotion is used in hand-washing exercises to show rigorous washing for at least 20 seconds is needed to rinse
away microbes. Place lotion on students’ hands and then have them wash for varying amounts of time from 5–20 seconds
before testing under black light.
Materials for Germ Transmission are available from Flinn Scientific, Inc.
Catalog No.
AP9080
AP9030
Description
Glowing Germ—Demonstration Kit
Ultraviolet Light Source, 18″
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
–2–
© 2010 Flinn Scientific, Inc. All Rights Reserved.
11000
Publication No. 11010
Digestive Enzymes Demo
Introduction
People must eat to live but how does the body transform food into the essential nutrients (peptides, amino acids, fatty acids,
and glucose) needed to carry out cell processes and cell growth? This demonstration introduces the biochemistry of digestion.
Concepts
• Catalysts
• Digestion
• Enzymes
• Gastrointestinal tract
Background
The human body is composed of millions of cells that need oxygen, water, and nutrients to survive. The amazing transformation of food into simpler molecules that can be absorbed for use by the cells is called digestion. Digestion occurs in the gastrointestinal (GI) tract. The GI tract is a mucous membrane-lined tube that extends from the mouth to the anus. While in the GI tract,
food is first mechanically broken down and then chemically treated with acids, bases, and enzymes within the organs of the digestive system. Enzymes are biochemical catalysts. A catalyst is any substance that causes a chemical reaction to occur without being
permanently altered in the process. A single molecule of a catalyst can perform the same reaction thousands of times in a single
second. Enzymes are globular, three-dimensional proteins with characteristic shapes that allow only a few specific substances
to temporarily bond with the enzyme. Because of the exclusive nature of
has amylase
enzyme/substrate binding, the human body contains thousands of different
mouth
digests
enzymes that are needed to catalyze all the different biochemical reactions
starch
that must occur.
In the stomach gastric juices containing mucus, hydrochloric acid,
pepsinogen, and small amounts of other enzymes continue the process of
digestion. Hydrochloric acid acts to denature (uncoil) the proteins in food
and activates pepsinogen, the inactive precursor of the enzyme pepsin.
Glucose, alcohol, fat-soluble drugs, some salts, and small amounts of water
are absorbed through the walls of the stomach directly into the bloodstream
for transport to the liver, where they are metabolized or sent on to other
cells in the body.
bolus
hydrochloric
acid and
pepsin
digests
into
glucose
has
stomach
protein
into
polypeptides
small
intestine
large
intestine
Once in the small intestine, the remaining food combines with enzymes
from the pancreas and epithelial cells of the small intestine and with bile
salts from the liver. The digestion of carbohydrates into glucose and other
simple sugars is completed in the small intestine by the enzymes sucrase,
maltase, lactase, and pancreatic amylase. The resulting sugars are absorbed
through the mucous lining of the small intestine into the bloodstream for
transport to the liver.
The partially digested proteins from the stomach are still too large to
be absorbed through the small intestine. Pancreatic juice contains three
glucose
chyme
Digestion begins in the mouth. The food mixes with saliva while the
teeth grind the food. Saliva provides the first chemical treatment of the
food. Saliva is composed of a neutral pH mixture of water, mucus, proteins,
mineral salts, and the enzyme amylase. Amylase begins the breakdown of
starch, a carbohydrate, into glucose (see Figure 1). Glucose is the sugar
used during cellular respiration as a source of cellular energy.
body
cells
has
elimination
enzymes
digests
digests
digests
carbohydrates
polypeptides
fats
into
monosaccharides
into
amino
acids
into
fatty acids
& glycerol
liver
Figure 1.
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11010
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peptidases that complete the digestion of protein into amino acids for absorption into the bloodstream. Each peptidase in the pancreatic juice is very specific and splits the bonds only between particular combinations of amino acids. Nucleases found in pancreatic juice convert the nucleic acids found in the food into nucleotides, which are also absorbed and transported to the liver.
Fats (lipids) are hydrolyzed into fatty acids and glycerol by intestinal and pancreatic lipase with help from bile salts secreted
by the liver. Hepatic cells of the liver produce bile, which is stored in the gall bladder before being excreted into the small intestine. Bile salts help with the digestion of fat globules by acting like soap. The globules of fat are small clumps of lipids that stick
together during digestion. Bile salts break the globules into smaller drops, creating greater surface area for pancreatic lipase to
break the lipids into fatty acids and glycerol which are also transported to the liver. The material remaining in the small intestine
travels to the large intestine where more mucous is added and where water and electrolytes are absorbed before the “waste” is
expelled from the body.
Materials (for each demonstration)
Albumin, 1 g
Starch solution, 0.5%, 100 mL
Amylase, 1 g
Water, deionized or distilled
Biuret test solution, 20 mL
Graduated cylinders, 100-mL, 3
Hydrochloric acid solution, 0.01 M, 50 mL
Marker
Iodine solution, I2/KI, 1 mL
Plastic cups, clear, 16-oz, 7
Pepsin, 0.5 g
Stirring rods
Safety Precautions
Biuret test solution contains copper(II) sulfate and sodium hydroxide and is a corrosive liquid. It is moderately toxic by
ingestion and is dangerous to skin and eyes. Hydrochloric acid solution is an eye and skin irritant. Iodine solution contains iodine
and potassium iodide and is an eye and skin irritant; it will stain skin and clothing. Avoid contact of all chemicals with eyes and
skin. Wear chemical splash goggles and chemical-resistant gloves and apron. Wash hands thoroughly with soap and water before
leaving the laboratory. Follow all laboratory safety guidelines. Please review current Material Safety Data Sheets for additional
safety, handling, and disposal information.
Preparation
Prepare the following solutions up to five days in advance of the lab.
• Use 100 mL of DI water to prepare a 1% albumin (protein) solution. Add 100 mL of the DI water to 1 g of albumin. Gently
mix and refrigerate. Note: Either egg or bovine albumin will provide accurate results however, bovine albumin is easier to
dissolve in water.
• The starch solution may either be purchased (Flinn Catalog No. S0151) or prepared. To prepare, boil 100 mL of DI water.
Add a small amount of the boiling DI water to 0.5 g of starch. Mix well, forming a paste. Continue to add 10 mL of boiling water to the bottle until the entire 100 mL of boiling water has been added. Allow the solution to slowly cool to room
temperature or refrigerate.
Prepare the following solution the day of the lab.
• Prepare a 1% pepsin solution by adding the 50 mL of 0.01 M hydrochloric acid to 0.5 g of pepsin. Mix well. The solution
should have a pH of 1.5 to 2.5.
• Use 100 mL of DI water to prepare 1% amylase solution. Add 100 mL DI water to 1 g of amylase. Mix well.
Procedure
Part A. Protein Digestion
1. Add 50 mL of the 1% albumin solution to each of two clear plastic cups.
2. Add 50 mL of DI water to one of the two plastic cups. Mix well.
3. Add 50 mL of the 1% pepsin solution to the second plastic cup. Mix well.
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© 2010 Flinn Scientific, Inc. All Rights Reserved.
11010
4. Wait 2 minutes before adding 10 mL of biuret test solution to each cup. Mix well.
5. Observe the color and appearance of the resulting solution in each cup and record the observations in the data table on the
Digestive Enzyme Demo Worksheet. Note: Biuret test solution is bluish-purple in the presence of polypeptides and lavender pink in the presence of amino acids.
6. Answer questions 1 and 2 on the Digestive Enzyme Worksheet.
Part B. Carbohydrate Digestion
7. Add 50 mL of the 1% starch solution to each of two clear plastic cups.
8. Add about 5 drops of iodine to each of the two clear plastic cups.
9. Add 50 mL of DI water to one of the two plastic cups. Mix well.
10. Add 50 mL of the 1% amylase solution to the second plastic cup. Mix well.
11. Observe the color and appearance of the resulting solution in each cup and record the observations in the data table on the
Digestive Enzyme Demo Worksheet. Note: Dark black color indicating a positive starch test will fade in the cup containing
the amylase solution as the enzyme digests the starch into sugars.
12. Answer questions 3 and 4 on the Digestive Enzyme Demo Worksheet.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and
review all federal, state and local regulations that may apply, before proceeding. Excess biuret test solution may be neutralized
with acid according to Flinn Suggested Disposal Method #10. Excess hydrochloric acid may be neutralized with base according
to Flinn Suggested Disposal Method #24b. Excess iodine solution may be reduced with sodium thiosulfate solution according to
Flinn Suggested Disposal Method #12a.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Evolution and equilibrium
Form and function
Content Standards: Grades 5–8
Content Standard A: Science as Inquiry
Content Standard C: Life Science, structure and function in living
Content Standard F: Science in Personal and Social Perspectives, personal health
Content Standards: Grades 9–12
Content Standard A: Science as Inquiry
Content Standard C: Life Science, matter, energy, and organization in living systems
Content Standard F: Science in Personal and Social Perspectives, personal and community health
Tips
• Biuret test solution does not contain the compound biuret. Biuret is the simplest compound that gives a positive test result
with biuret test solution.
• Catalysts cause slow reactions to occur more quickly by lowering the activation energy necessary for the reaction to occur.
A ski lift is an analogy for a catalyst. If the reaction is “skiing,” then the skier must first get to the top of the ski hill. One
option is for skiers to climb to the top and once they reach the top, enjoy the potential energy they earned as they ski back
down the hill. The ski lift allows many more skiers to reach the top of the hill very quickly without the skiers expending
much energy. Once at the top, they still enjoy the same energy release as they ski down the ski hill. The reaction can occur
many, many more times and the ski lift (the catalyst) is not changed during the process.
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© 2010 Flinn Scientific, Inc. All Rights Reserved.
11010
• For an advanced class you may want to use this activity to introduce the terms substrate, active site, cofactors, coenzymes,
and the induced fit theory.
• In order to help students understand that amylase is found in saliva, have each student chew on an unsalted, unsweetened
saltine type cracker until the cracker tastes sweet. The sweetness is due to the amylase hydrolyzing the starch into glucose
and other mono- and disaccharides. Complete this activity in a food-appropriate area.
Sample Data Table (Student data will vary.)
Cup Contents
Observations
Protein, water, and biuret
Bluish-purple, cloudy
Protein, pepsin, and biuret
Pinkish-purple, clear
Starch, water, and iodine
Dark blue-black
Starch, amylase, and iodine
Brown
Answers to Questions (Student answers will vary.)
1. Compare and contrast the observations of the biuret test results. Describe the evidence, if any, for the digestion of protein
using pepsin.
The cup containing protein solution, water and biuret test solution is the negative control. The solution is a cloudy, bluepurple color indicating this cup is positive for polypeptides. The cup containing protein solution, pepsin and biuret is a
clear, pink-purple color. Pepsin digests the albumin protein leaving peptides which gives a pink-purple biuret test.
2. The pepsin solution was prepared using 0.01 M hydrochloric acid in order to optimize the pepsin enzyme. Why was this
necessary?
Pepsin is active in the acidic environment of the stomach. A basic or neutral pH would inactivate the enzyme.
3. Compare and contrast the iodine test results for starch and starch/amylase. Explain the test results based on the activity of
amylase.
The cup containing the starch, water, and iodine solution is the control sample yielding a positive iodine test for starch.
The remaining cup contains starch, amylase, and iodine. It has a negative iodine test because the amylase has hydrolyzed
the starch to glucose.
4. Summarize the digestion of a steak and baked potato dinner. Indicate the enzymes responsible for digestion in the mouth,
stomach, and small intestine for the protein and starch components of the meal.
Amylase in the mouth starts digesting the starch of the baked potato. Pepsin and acid begin digesting the steak proteins in
the stomach. The carbohydrates (starch) leave the stomach first and are digested into simple sugars in the small intestine
by sucrase, maltase, lactase, and pancreatic amylase. The protein digestion of the steak continues in the small intestine
when the three peptidases finish splitting the protein into amino acids for absorption into the bloodstream. Nucleases
in the small intestine convert nucleic acids into nucleotides. Finally, fats are hydrolyzed into fatty acids and glycerol by
lipases in the small intestine.
Materials for Digestive Enzymes Demo are available from Flinn Scientific, Inc.
Catalog No.
FB1862
A0300
A0283
B0051
H0014
I0038
P0006
S0151
Description
Digestive Enzymes at Work—Student Laboratory Kit
Bovine Serum Albumin, 10 g
Amylase, 10 g
Biuret Test Solution, 500 mL
Hydrochloric Acid Solution, 0.1 M, 500 mL
Iodine–Potassium Iodide Solution, 100 mL
Pepsin, 25 g
Starch Solution, 0.5%, 500 mL
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
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© 2010 Flinn Scientific, Inc. All Rights Reserved.
11010
Name: ____________________________________
Digestive Enzyme Demo Worksheet
Data Table
Cup Contents
Observations
Protein, water, and biuret
Protein, pepsin, and biuret
Starch, water, and iodine
Starch, amylase, and iodine
Questions
1. Compare and contrast the observations of the biuret test results. Describe the evidence, if any, for the digestion of protein
using pepsin.
2. The pepsin solution was prepared using 0.01 M hydrochloric acid in order to optimize the pepsin enzyme. Why was this
necessary?
3. Compare and contrast the iodine test results for starch and starch/amylase. Explain the test results based on the activity of
amylase.
4. Summarize the digestion of a steak and baked potato dinner. Indicate the enzymes responsible for digestion in the mouth,
stomach, and small intestine for the protein and starch components of the meal.
11010
© 2010 Flinn Scientific, Inc. All Rights Reserved.
Publication No. 11003
Ozone Test Paper
Introduction
We have become all too familiar with “smog-alerts” and television reports asking for us to reduce vehicle traffic due to high
ozone levels. How can we test for ozone? Why is it so bad?
Concepts
• Ozone
• Parts per million/billion
• Air pollution
Background
Our atmosphere is divided roughly into two layers—the troposphere (between 0–9 kilometers above the Earth’s surface)
and the stratosphere (9–15 kilometers above the Earth’s surface). About 90% of all natural ozone (O3) gas exists in the upper
stratosphere.
This so-called “ozone layer” plays a key role in the Earth’s balance, by providing a protective shield for living things against
harmful ultraviolet (UV) radiation from the Sun. The effects of high levels of UV radiation include risks of cancers, cataracts,
immune deficiencies, damage to plants, and other genetic consequences. In the lower levels of the atmosphere (troposphere) ozone
plays a destructive role as an irritant in smog.
In the stratosphere, ozone is usually found in concentrations of about 10–15 parts per million. Tropospheric ozone usually
occurs at about 120 parts per billion. Tropospheric ozone is formed when hydrocarbons and nitrogen oxides from forests, industries and automobile exhaust react with heat and sunlight. In years past, tropospheric ozone didn’t seem to be affecting human
health. But the quantity of ozone that has been recently produced by certain human activities has caused us to rethink acceptable
ozone levels. The concentrations have increased to such high levels that ozone has become a real irritant.
While stratospheric ozone shields us from UV radiation, ozone in the lower troposphere is irritating and destructive to forests, crops, nylons, rubbers and other materials. High concentrations of ground level ozone injure or destroy living tissue and can
be harmful to individuals with respiratory problems. Thus, we have a dual ozone problem—pollution or smog in the troposphere
(“bad ozone”) and depletion of the ozone layer in the stratosphere (“good ozone”). These are two very different problems, both
stemming from human industrial and other activities.
Since 1900, the amount of ozone near the Earth’s surface has more than doubled. In urban areas in the Northern Hemisphere,
high ozone levels usually occur during the warm, sunny summer months from May to September. Typically, ozone levels reach
their peak late in the afternoon, after the Sun has had time to fully react with the exhaust fumes from cars. Tropospheric ozone is
formed by the interaction of sunlight with hydrocarbons and nitrogen oxides which are emitted by automobiles and other industrial activities.
Christian Schoenbein discovered ozone in 1839. He established the presence of ozone in the air and demonstrated that it is
a natural component of the air. He developed a way to measure ozone in the air using a mixture of starch and potassium iodide
spread on filter paper. Schoenbein’s paper can be made and his original test for ozone duplicated. The Schoenbein test is based
upon the oxidizing ability of ozone—ozone is a stronger oxidizing agent than normal oxygen (O2). Ozone in the air will oxidize
potassium iodide on the test paper to produce iodine. The iodine in turn reacts with starch, staining the paper a shade of purple.
The intensity of the purple color will depend upon the amount of ozone present in the air. The darker the color of the paper, the
more ozone present at that location. Two reactions are involved:
2KI + O3 + H2O → 2KOH + O2 + I2
I2 + starch → I2–starch complex
(purple)
EARTH SCIENCE-FAX姠. . .makes science teaching easier.
IN11003
012210
Materials
Corn starch, 5 g
Glass plate or other flat drying surface
Potassium iodide, KI, 1 g
Graduated cylinder, 100-mL
Water, distilled or deionized, 100 mL
Hot plate
Bag, resealable type (optional)
Paper clips
Beaker, 250-mL
Paint brush
Envelope (optional)
Sling psychrometer or other humidity measuring device
Chromatography paper, 8″ × 8″
Stirring rod
Safety Precautions
Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap
and water before leaving the laboratory. Follow all laboratory safety guidelines. Please review current Material Safety Data
Sheets for additional safety, handling and disposal information.
Procedure
Part A. Ozone Test Paper
1. Weigh 5 g of corn starch and transfer the corn starch to a 250-mL beaker.
2. Measure 100 mL DI water in a graduated cylinder.
3. Add a small amount of DI water to the corn starch and stir well. Repeat this step several times until a thin paste is formed.
Add the remainder of the 100 mL of DI water to the corn starch paste.
4. Heat the corn starch and water on a hot plate. Stir frequently with a stirring rod until the corn starch mixture starts to gel.
The mixture is gelled when it thickens and becomes somewhat translucent.
5. Carefully remove the beaker from the hot plate and add 1 g of potassium iodide. Stir well. Let the solution cool.
6. Place a piece of filter paper on a glass plate or other flat, washable surface.
7. Using a paint brush, spread the starch/potassium iodide solution evenly on one side of the filter paper.
8. Turn the filter paper over and repeat. Note: Apply the paste as uniformly as possible.
9. The paper can be used for testing at this point (proceed to Part B) or it can be readied for storage as described below.
10. Allow the paper to dry. Do not set it in direct sunlight. It can be air-dried overnight or the process can be shortened by
placing the paper in a low-temperature drying oven.
11. When the paper is completely dried, cut the filter paper into 1-inch strips.
12. Store the strips in an envelope placed inside a resealable bag. Note: Keep strips out of direct sunlight.
Part II. Testing for Ozone
13. If the test strip is wet from Part A, continue on to the next step. If the paper was dried in Part A, dip a strip of the dried
ozone test paper in DI water to reactivate before proceeding to the next step.
14. Unfold a paper clip to make a hook on which to hang the ozone test strip.
15. Select an area without drafts and direct sunlight where the ozone test strip can hang freely from the paper clip hook.
16. Determine the relative humidity at the data collection site using a sling psychrometer or other humidity measuring device.
17. Expose the ozone test paper for at minimum of eight hours or overnight.
18. When the strip is retrieved, either seal it in a resealable bag for testing back at the lab or proceed to the next step.
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© 2010 Flinn Scientific, Inc. All Rights Reserved.
11003
19. To observe the test results, dip the paper in DI water. Observe the color and determine the Schoenbein Number using the
Schoenbein Number Scale below.
0–3
No change to little change
4–6
Pink to lavender hues
7–10
Blue to purple
Schoenbein Number Scale
20. Refer to the Relative Humidity Schoenbein Number Chart below. Along the bottom of the chart, find the point that corresponds to the Schoenbein number recorded above. From that point draw a line upward until it intersects the curve that
corresponds to the relative humidity recorded above. To find the ozone concentration in parts per billion, draw a line perpendicular from the intersection point to the vertical axis on the chart. Record the ppb number for the test site.
Relative Humidity Schoenbein Number Chart
20%
30%
40%
50%
60%
180
160
140
70%
Ozone ppb
120
100
80%
80
60
90%
40
100%
20
00
1
2
3
4
5
6
7
Schoenbein Number
8
9
10
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and
review all federal, state and local regulations that may apply, before proceeding. Excess starch/potassium iodide solution may be
disposed of according to Flinn Suggested Disposal Method #26b.
Connecting to the National Standards
This laboratory activity relates to the following National Science Education Standards (1996):
Unifying Concepts and Processes: Grades K–12
Evidence, models, and explanation
Constancy, change, and measurement
Content Standards: Grades 5–8
Content Standard B: Physical Science, properties and changes of properties in matter
Content Standard D: Earth and Space Science, structure of the Earth system
Content Standard F: Science in Personal and Social Perspectives, natural hazards, risks and benefits
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© 2010 Flinn Scientific, Inc. All Rights Reserved.
11003
Content Standards: Grades 9–12
Content Standard B: Physical Science, chemical reactions
Content Standard D: Earth and Space Science, energy in the Earth system
Content Standard F: Science in Personal and Social Perspectives, personal and community health, environmental quality,
natural and human-induced hazards
Tips
• Plan carefully for the ozone test sites. Select areas where the test strips can be hung inconspicuously and undisturbed during the test time frame. Locations should be convenient to reach during class time or after school. Obtain permission or
clearance for all sites as needed.
• This activity works best in areas of low humidity and high ambient ozone concentrations. In some parts of the country
(especially rural areas) this activity may not produce very conclusive or interesting results.
• Check with local authorities to secure ozone readings for the days you conduct this activity. Have students compare their
data with the scientific data. The actual ozone number is not critical. The relative amount of ozone is interesting and the
relative comparisons of various locations can be very revealing. (Near freeways, copy machines, electrical outlets, etc.)
• Ozone has an acrid odor. Older electronic equipment, ozone generating air cleaning machines, and small motors may provide interesting ozone results.
Materials for Ozone Test Paper are available from Flinn Scientific, Inc.
Catalog No.
FB1619
AP5069
S0124
P0278
AP4299
Description
Make Your Own Ozone Testing Kit
Pocket Sling Psychrometer
Starch, Corn, 500 g
Potassium Iodide, 100 g
Chromatography Paper, Pkg. of 100 sheets
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
–4–
© 2010 Flinn Scientific, Inc. All Rights Reserved.
11003