Aleks , problem set, and lab write up

The Chemistry of FoodPreparation for Lab
Read the lab procedure and answer the embedded questions. You may need to consult
your textbook as well as the supplementary materials posted on Canvas. Note that you will
not be turning in the embedded questions as part of your lab write-up. Instead, use these
embedded questions to guide your preparation for the experiments.
1. Covalent bonds occur when atoms share…
2. Building a molecule from simpler components is called anabolism. Breaking a
substance down is called…
3. The protein in gelatin that allows it to form a gel is called…
4. An enzyme in pineapple capable of digesting the protein in gelatin is called…
5. For each of the following substances, identify whether it is a carbohydrate, lipid,
protein, or “other”.
i. vegetable oil
ii. lactase
iii. amylase
iv. starch
v. lactose
vi. distilled water
6. Each of the following statements applies to one of the tests we will perform in Part III of
this lab. Give the name of the appropriate test.
i. Uses strips that change color in the presence of the test substance
ii. Requires that the test solution be heated
iii. A very dark colored solution indicates that a lot of starch is present
7. Developing predictions: If the lactase enzyme is effective in breaking down lactose,
would you expect to see a positive or negative result for the glucose test (“positive” =
glucose is present)? Explain.
8. Developing predictions: If the amylase enzyme is effective in breaking down the cracker,
would you expect to see a positive or negative result for the presence of starch?
Explain.
The Chemistry of Food
Courtesy of Grace Sparks, Seattle Central Community College, and J. Walny, A.
Rubenstein, and E. Matthews, Michigan State University.
Carbohydrates, lipids, and proteins are relatively large molecules that play many important
roles in living organisms. The basic framework or “backbone” of all these macromolecules
consists of carbon atoms.
• Why is carbon a particularly useful element to form large molecules?
In lab, we will use a suite of chemical tests to 1) detect the types of molecules present in
various food items, and 2) study how enzymes affect the molecules present in food items.
Learning Objectives
● Make accurate conclusions on the macromolecule content of food based off of your
experimental results.
● Learn and apply the proper terminology to describe the molecular structure of the 4
major categories of biological macromolecule.
● Learn how to utilize positive and negative controls in the interpretation of
experimental results.
Background: Biological Macromolecules
Carbohydrates come in several basic forms.
The simplest sugars are called
monosaccharides, and they contain 3-7 carbon
atoms, often bonded together in a ring structure.
Glucose is a very common 6-carbon sugar.
When two monosaccharides bond together, they
form a disaccharide, such as sucrose. Many
monosaccharide subunits bonded together forms
a polysaccharide, a much more complex
carbohydrate. Starch, cellulose, and glycogen
are common examples of polysaccharides. Our
test methods will allow us to easily detect starch and also reducing sugars (detected when
copper is reduced to give a red color). Glucose and fructose should test positive, but
sucrose (a disaccharide) may not.
• If the disaccharide sucrose is made of a glucose bonded to a fructose, do you think
copper will give a red color after sucrose is broken down by heat or acid?
There are many different types of lipids. They are
all grouped together as lipids because at least some
part of the molecule does not dissolve in water. Oil
and vinegar salad dressing requires vigorous shaking
because the oil and vinegar (which is a water-based
solution) do not mix well. We will use a simple test to
help determine whether or not lipids are present in
our samples.
Most proteins are very large
molecules with complex
shapes. These shapes are
formed by the interactions
among many amino acids
subunits bonded in a long
Insulin, a signaling protein,
chain. Amino acids join to one
represented in two ways.
another by a specific type of
covalent bond called a peptide bond.
Proteins serve many functions, including structures, signaling, and facilitating chemical
reactions. Each function is dependent upon the protein’s folded shape. Proteins that are
chemical catalysts are called enzymes. Please note that not all enzymes are proteins, but
most are!
Read the following protocols to understand how we will test for various biological
macromolecules and observe how enzymes can break them down.
Lab Protocol
1.
Enzymatic activity of saliva.
Background: As food is broken down by the
teeth by way of chewing (the process of
mastication), saliva is provided by the salivary
glands. This is where chemical digestion
begins. Saliva, among other important
substances, contains an enzyme called amylase
that aids in the breakdown of the polysaccharide
starch. Enzymes are strings of amino acids,
joined by peptide bonds, that are responsible for
catalyzing both synthesis (anabolic) and
decomposition (catabolic) reactions. Amylase
breaks up long starch molecules into smaller
sugar molecules.
Objective: Investigate enzyme activity for an enzyme that breaks down polysaccharides.
Materials:
●
●
●
●
●
Fresh Saltine Crackers
Iodine Test Reagent
Benedicts Test Reagent
Hot Water Bath (90°)
Test Tube Holder (1 per
group)
● Test Tubes (4 per group)
● Sample Cups (2 per
group)
● Spatula
● Razor Blade
● positive and negative
controls for both tests (at
instructor’s station)
Procedure:
Now you will test both an unchewed cracker and a chewed cracker for the presence of
sugar and the presence of starch. Here’s how:
1.
First, chew a cracker for one full minute, then spit it into one of the sample cups.
Add enough water to bring it to at least 1 mL.
2.
In a new sample cup, add an unchewed cracker (the same size as the chewed
one), and break it up using a spatula. Add enough water to bring it to at least 2 mLs.
3.
Using a 1 mL pipette with the end cut off 0.5 cm from the tip (your instructor can
show you how), transfer 1 mL of each sample to two labeled test tubes, one for the
Benedict’s test and one for the starch test. You will need to do this for each of the two
samples. When you are finished, you should have a total of 4 tubes to which you will
now be ready to add the test reagents.
4.
Testing for Sugar (Benedict’s Test)
a.
Using a 1 mL pipette, add 1 mL of Benedict’s solution to each of the
cracker sample tubes.
b.
Heat the test tubes (use test tube holder) for 3 minutes in a hot water bath.
c.
Compare with the class positive and negative controls to determine
whether the polysaccharide has been broken down into monosaccharides. A
cloudy precipitate will form that varies from green to yellow to orange to red to
brown in color depending on the concentration of monosaccharides.
5.
Testing for Starch (Iodine Test)
a.
Add 2 drops of iodine to a tube with 1 mL of chewed or unchewed cracker
(the ones you set up in step 3).
b.
Compare with the class positive and negative controls to determine
whether any starch is still remaining (i.e. not yet broken down to sugar). If it
changes color to dark blue or black, starch is present. If the color is brown, no
starch is present.
6.
Answer the questions for this week’s lab write-up.
2.
Pineapple flavored Jello?
Background: Gelatin is obtained from selected pieces of calf
and cattle skins, demineralized cattle bones (ossein), and
pork skin. Contrary to popular belief, hoofs, horns, hair,
feathers, or any keratin material is not a source of gelatin.
There are two forms of gelatin: Type A, derived from acid
processed materials—primarily pork skin; and Type B, derived
from alkaline or lime processed materials—primarily cattle or
calf hides and ossein.
Collagen fibers are made
by the twisting together of
three amino acid chains:
Gelatin is made from a protein
called collagen, a long, fibrous
protein which comes from the
joints of animals. Gelatin
dissolves in hot water and
congeals (jells) at cooler
temperatures. As the
dissolved gelatin mixture cools, the collagen forms into a
matrix that traps the water. As a result, the mixture turns into
the jiggling, wriggling pseudo-solid that we all know and love as Jell-O™.
The pineapple belongs to a group of plants called Bromeliads. The enzyme in fresh
pineapple that is responsible for the breakdown of collagen is bromelain. The process
of canning pineapple denatures (unfolds) the bromelain in such a way that it can no
longer catalyze the breakdown of gelatin.
Objective: Investigate enzyme activity for an enzyme that breaks down proteins.
Materials:
●
Sample Cups (2 per group)
●
Jell-O™ Liquid (sugar free)
●
Fresh Pineapple (1 piece per group)
●
Canned Pineapple (1 piece per group)
Procedure:
1.
Observe the sample cups containing the canned pineapple and fresh pineapple.
These were prepared 24 hrs ago by adding a piece of either fresh or canned pineapple
to a cup of Jell-O.
2.
Answer the questions for this week’s lab write-up.
3.
Lipids, water, and soap!
Background: One of the most important characteristics of fats and lipids, in general, is
their insolubility in water due to their non-polar nature. Lipids are made of long chains
of hydrocarbons with relatively little oxygen atoms. As a result, they tend to be nonpolar and therefore do not dissolve in polar substances such as water. (“Like dissolves
like.”) Polar or charged substances can be dissolved in polar substances and non-polar
substances can be dissolved in non-polar substances.
In our digestive systems, lipids are, in part, broken down by bile, which is produced by
the liver and aids in the digestion of fats in the small intestine. Bile is not an enzyme,
but it does help the enzymes do their job. Bile helps create microscopic fat globules (a
process called emulsification).
Emulsification is important because it allows lipases (important digestive enzymes
that break down fats) to attack and break down the smaller fat globules. Larger fat
globs would mean that the lipases could not access the fats (lipids) on the interior of the
lipid globs.
In this lab, you will use soap to mimic the action of bile. Soap is unique in that a soap
molecule has a polar (charged) end and a non-polar (non-charged) end. The non-polar
end interacts with and dissolves grease, oil, or fat, while the polar end interacts with a
polar substance such as water molecules. In this way, it can separate lipid molecules.
Objective: Investigate the behavior of lipids and use soap to mimic the action of bile.
Materials
●
Clean Test Tubes (2 per group)
●
Water
●
Vegetable Oil
●
Dish Soap
Procedure:
1.
Obtain two clean test tubes (no soap or oil).
2.
Fill each 1/3 full with water.
3.
Fill each 1/3 full with oil.
4.
Add about 1 drop of soap to one of the test tubes.
5.
In your lab notebook, draw a “before” picture of the two test tubes.
6.
Cover the openings of the test tubes with hands/fingers and shake them
vigorously.
7.
In your lab notebook, draw an “after” picture of the two test tubes.
8.
Answer the questions for this week’s lab write-up.
4.
Lactose intolerance and glucose.
Background: Lactose is the sugar found in milk and therefore has the common name
“milk sugar.” Lactose is a disaccharide composed of glucose and galactose sugar
subunits. When humans ingest milk, lactose must be broken down into glucose before
it can be used as an energy source. The enzyme responsible for breaking down or
“digesting” lactose is called lactase.
Normally, all people are born with the ability to make lactase and can easily digest the
lactose in mother’s milk and later in dairy products. However, for some people,
increasing age means loss of the production of lactase. Loss of lactase production can
begin as early as two years of age in some individuals and appears to occur more
frequently and earlier in individuals of African or Asian heritage. Individuals who do not
produce lactase cannot break down the sugar lactose into its component parts.
Since only glucose passes from the intestines into the blood, lactose sugar remains in
the intestinal tract until it leaves the body in the feces. The lactose, however, is used as
an energy source by the fermentative bacteria present in the intestines. As a result of
the bacteria’s fermentation, gas is released. This can cause bloating, cramps, and
diarrhea. Lactaid and similar over-the-counter medications contain the enzyme lactase.
When these pills are taken in sufficient amounts with dairy products, people who are
normally unable to enjoy dairy products can digest lactose and avoid the uncomfortable
side effects they normally experience.
Diabetics have a problem where excess glucose appears in the blood and urine,
causing damage to organs like the eyes and kidneys. To monitor this glucose, test
strips are sometimes used to test the urine for excess glucose. A chemical indicator on
the end of the dipstick changes color in the presence of glucose. The glucose test
strips that you will be using turns from pink (no sugar) to dark purple (presence of
sugar). Note: An indicator is a substance that changes color in the presence of a
particular chemical. There is an additional indicator at the end of each strip that tests
for the presence of albumin, a protein, but you can disregard it for this test.
Objective: Investigate the enzyme activity of an enzyme that breaks down a
disaccharide into two monosaccharides.
Materials
●
Glucose Test Strips (2 per group)
●
Sample Cups (1 per group)
●
Lactaid Pills (1 per group)
●
Milk
Procedure:
1.
Answer the first question for this exercise in your lab write-up before proceeding
with the lab activity.
2.
Fill a sample cup 1/3 full of plain milk.
3.
Test the plain milk with a glucose test strip and record the results in your lab
notebook.
4.
Crush up ½ of a Lactaid pill with a mortar and a pestle.
5.
Add the pill powder to the milk.
6.
Stir with a fresh glucose test strip (10 seconds minimum) and record the results
in your lab notebook.
7.
Answer the remaining questions for this week’s lab write-up.
Lab Write-Up:
You may work together to answer these questions in lab. For your lab write-up, type
your final answers (using complete sentences) into a separate document.
(Part 1) Enzymatic activity of saliva.
1. For the chewed cracker…
a. What color was produced by the Benedict’s test?
b. What color was produced by the Iodine test?
2. For the unchewed cracker…
a. What color was produced by the Benedict’s test?
b. What color was produced by the Iodine test?
3. According to the above results…
a. What type of carbohydrate(s) (monosaccharides and/or polysaccharides) was
(were) present in the chewed sample?
b. What about the unchewed cracker?
4. Does the amylase enzyme catalyze a catabolic or anabolic reaction? Briefly explain
your choice in one complete sentence.
(Part 2) Pineapple-flavored Jello-O?
5. What is the consistency (i.e. texture) of the Jell-O made with the canned pineapple
compared to the Jell-O made with fresh pineapple? What does this tell you about
the reaction that has occurred?
6. Which of the 4 types of biological macromolecule allows Jell-O™ to form a gel?
7. In terms of an enzymatic reaction, is collagen a substrate, an enzyme, or a product?
(see figure 8.13 in your book for help)
8. In terms of an enzymatic reaction, is bromelain a substrate, an enzyme, or a
product? (see figure 8.13 in your book for help)
9. Briefly describe what happens during the cooking of pineapple that affects its
interaction with Jell-O™.
10. What class of monomers (subunits) will the collagen break down into?
11. Fresh pineapple is used as a meat tenderizer. Based on the results of our study,
explain why.
(Part 3) Lipids, water, and soap!
12. Compare your drawings of the oil/water tube and the soap/oil/water tube before and
after shaking. How are the contents of the test tubes different after shaking?
13. Soaps contain amphipathic molecules, molecules that have distinct polar and nonpolar regions. How does this property explain your observations in the “Lipids,
water, and soap” experiment?
14. Look up “bile” in your book. It is a substance manufactured by your gall bladder to
help digest food. What category of biological macromolecule would bile help digest?
15. If bile is not an enzyme, then briefly describe how it helps you digest food?
(Part 4) Lactose intolerance and glucose.
16. If lactase (Lactaid) is added to milk, what should happen?
17. According to your tests, which had a higher concentration of glucose: milk or milk +
Lactaid?
18. The “-ose” ending suggests that lactose is a(n) __________________________.
19. The “-ase” ending suggests that lactase is a(n) __________________________.
20. Is the reaction catalyzed by lactase catabolic or anabolic?
Problem Set III
DNA Structure
TBIOL 130 (Winter ‘23)
Name:
Score:
Answer the following questions to the best of your ability; this exercise is worth 30 points and must be uploaded to Canvas
by midnight on Friday of Week 4 (Jan. 27th). You may work together with a group to complete this exercise, but everyone
must submit their completed problem sets separately. Please note that “work together with a group” does not mean that
you can submit identical answers. In other words, you can consult with your peer(s) on the answer (or the means to come
up with the answer) but you need to answer the questions in your own words.
You may provide your answers in a separate file or within this worksheet (save as a .pdf file) but for the latter, remember
to TYPE YOUR ANSWERS IN RED (or another color of your choice)!
1. You are a graduate student aiming to develop new antibiotics, small organic molecules that bind to and prevent
the activity of proteins involved in processes essential for cell survival or cell division. The data below was
generated after an experiment, where you added a new antibiotic candidate (“drug”) to cultures of bacteria
(prokaryotic cells) or cancer cells (eukaryotic cells). Over a period of 48 hours, you monitored cellular growth
(sampling every 3 hours) and determined how many cells (“cancer” or “bacteria”) were present in your cultures
(measured in cells/mL) after the addition of your candidate antibiotic (“+ drug”) or water (“no drug”). Answer
the questions below based on your interpretation of the data.
• Please note that the use of cancer cells as a measure for how eukaryotic cells would respond to a new
drug treatment is quite common in molecular and cellular biology. You will learn more about the use of
cancer cells to establish immortalized cell lines in Cellular Biology (TBIOL 303) but for now, assume that
the cancerous nature of the eukaryotic cells is irrelevant to the outcome of the experiment. In other
words, any effect observed in these cells will be the result of the drug treatment (and NOT the fact that
these are cancer cells).
a. (1.5 points) State a hypothesis (or the predicted outcome of the experiment) that you could have been
testing using this experimental set up.
Problem Set III
DNA Structure
TBIOL 130 (Winter ‘23)
b. (3 points) Were the eukaryotic cells affected by the drug treatment? Briefly explain how you know this
information. You must refer to the graph as part of your answer.
c. (3 points) Were the prokaryotic cells affected by the drug treatment? Briefly explain how you know this
information. You must refer to the graph as part of your answer.
d. (4 points) You decide to submit your data for publication in the Journal of Bacteriology but Reviewer #2 has
requested an additional experiment to confirm your results. They suggest that you add the drug BEFORE the
prokaryotic and eukaryotic cells have reached stationary phase (indicated by the growth curves “leveling
out” towards the end of the 48-hour period in previous graph). In other words, they wanted to see the
effect when the drug is added after cellular growth/replication has already started. Assuming you added
your antibiotic candidate mid-way through the experiment (indicated by red arrow), predict what the
bacterial and eukaryotic growth curves would look like based on your previous results. Briefly explain your
answer.
Problem Set III
DNA Structure
TBIOL 130 (Winter ‘23)
e. (4.5 points) Below are four different commercially-available antibiotics used to treat various bacterial
infections. Each antibiotic targets a different macromolecule, resulting in a halt of cellular division and/or
cell death. Briefly research each antibiotic and determine what macromolecule is ultimately affected by the
drug and why this would be detrimental to the bacterial cell. Portions of this table have been filled out for
you.
Antibiotic Drug
Ampicillin
Macromolecule Affected
(Specific Target)
Effect on Bacterial Cell
Polysaccharide (peptidoglycan)
Antibiotic targets transpeptidase, an enzyme necessary for
the synthesis of peptidoglycan (the polysaccharide
component of cell wall). Since the bacteria cannot
complete the biosynthesis of peptidoglycan, they cannot
complete binary fission and lyse as a result.
Polymyxins
Ciprofloxacin
Tetracycline
BONUS (1 point): Haemophilus influenzae is a Gram-negative bacterium that infects the upper respiratory track and was
once thought to be the causative agent of influenza (back before the influenza virus was identified as the cause of the
disease). Unfortunately, you and your friend James come down with flu-like symptoms over winter break but while James
is diagnosed with an H. influenzae infection, you are diagnosed as having influenza. As you leave the hospital, James is
prescribed the antibiotic Cefotaxime and he insists that you take the medication even though you have been sent home
with instructions to “rest up and drink plenty of fluids.” Briefly explain to James why your influenza infection must be
treated differently than his H. influenzae infection? In other words, why shouldn’t you take antibiotics to combat viral
infections?
Problem Set III
DNA Structure
TBIOL 130 (Winter ‘23)
2. Mice are often used as model organisms to study the genetics underlying aspects of development and disease
owing to their high levels of evolutionary conservation/genetic relatedness to humans. With that in mind, the
data below was generated in an experiment using cells isolated from two different laboratory mice strains
(mouse #1 and mouse #2). The cells that you isolated from the mice were cultured (in a plastic petri dish with
appropriate nutrients and growth factors to promote their growth and survival) in the laboratory for several
weeks and had been split into several different dishes when you notice a little problem. Some of the mouse #2
dishes have cells that are almost all dead and other mouse #2 dishes contain cells that are dividing much more
rapidly than the cells from mouse #1.
Panel A shows blue-fluorescently stained metaphase chromosomes from the mouse #1 and mouse #2 cells. Panel B
shows the relative fraction of cells found at different phases of mitosis. In a separate experiment (data not shown), you
determined that equal fractions of each cell culture were dividing at the same moment in time but determined that they
were progressing through mitosis at different rates.
a. (2 points) What looks different when you compare the chromosomes from mouse #1 and mouse #2 cells
(Panel A)?
b. (2 points) Describe the results shown in Panel B. Refer to Chapter 12 of your textbook if you need to review
cell cycle and the stages of mitosis.
c. (4 points) How might the difference described in question #2A underlie the results described in question
#2B? Discuss the connection between chromosome structure and cell cycle progression as part of your
answer.
Problem Set III
DNA Structure
TBIOL 130 (Winter ‘23)
d. (3 points) Based on the information provided here, provide a hypothesis that may explain why some of the
mouse #2 cells are dying off.
e. (3 points) Propose a follow-up question that you could address using these cells that would build on the
results shown here and allow you to better understand the relationship between mouse #2 genetic/physical
traits and chromosome condensation or progress through mitosis.