BIOL251 – Cell Biology
Exam #1
NAME: __________________________________
Obesity is a health risk in many parts of the world. In
an attempt to combat this phenomenon, many
different food additives have been developed as a
means of reducing the caloric value of foodstuffs.
Xylitol: A sugar alcohol used as an artificial
sweetener
Xylitol is an artificial sweetener that simulates the
same sweet sensation as common sugars, such as
sucrose. However, Xylitol has a much lower caloric
value both chemically as well as physiologically as it
is absorbed/metabolized by humans more slowly
than sucrose.
As a side-note, dental carries (cavities in your teeth)
are also a problematic result of eating foods high in
sugar. The sugar is metabolized by bacteria in your
mouth resulting in the generation of acid. This
lowering of the pH surrounding the teeth causes
degradation of the protective outer layer of enamel
on teeth and can result in cavities.
Xylitol is often advertised as both low-calorie as well
as something that prevents tooth decay.
1. Based on the above information, what is the most
likely explanation for Xylitol’s purported
promotion of dental health?
a. Xylitol forms a protective barrier around the
teeth, preventing decay.
b. Xylitol triggers a cell signaling cascade that
causes teeth to generate more enamel than
normal.
c. Oral bacterial cells, like human cells, are
less able to absorb and metabolize xylitol
when compared to normal sugar, like
sucrose, resulting in less acid formation
and thus less tooth decay.
d. Xylitol acts as a mutagen, damaging bacterial
DNA in the oral cavity, preventing tooth
decay.
Tuesday, 14 Feb 2022
Under normal circumstances, eating sugar triggers
the release of insulin in humans. Insulin then tells
cells to take up sugar out of the blood stream.
Diabetics have malfunctioning insulin signaling –
either they lack the ability to make insulin (type I
diabetes) or their cells no longer respond properly to
insulin signaling (type II diabetes). In both cases,
since insulin signaling is not fully functioning, they
can suffer from hyperglycemia, that is, aberrantly
high levels of sugar in the bloodstream, while the
cells in the body that need that sugar starve.
There is a very weak insulin response to ingestion of
xylitol, relative to normal starches and sugars.
Interestingly, however, dogs have a massive insulin
response to the sweetener to the point where
relatively small amounts of it can be fatal. Ingestion
of xylitol by dogs triggers a massive release of
insulin that causes the dog’s cells to take up a large
proportion of sugar out of the bloodstream, leading
to hypoglycemia, that is, very low amounts of sugar
in the blood. Animals suffering from hypoglycemia
can suffer from weakness, seizures, and coma. Do
not let your dog get into any food/gum that contains
xylitol.
2. Based on the above information, what is the most
likely explanation for how xylitol exhibits such a
different response in dogs relative to humans?
a. Xylitol’s antimicrobial properties damaged
the canine microbiome to the point that it
causes organ failure.
b. Dogs are genetically distinct from humans
and thus may have different forms of the
genes that respond to molecules like xylitol
and sugar, explaining the toxic effects of
xylitol.
c. Dogs do not normally eat sugars, therefore
consumption of high-sugar foods is generally
toxic to dogs.
d. Dogs likely have enzymes that convert
xylitol to a toxin that triggers DNA damage
in important cells that results in organ failure.
3. The reduced caloric benefit of xylitol has been
established, however, more work is needed to
fully support the hypothesis that xylitol promotes
dental health. What would be the most
appropriate means of testing whether or not
BIOL251 – Cell Biology
Exam #1
xylitol is better for dental health than other
dietary sugars?
a. A retrospective analysis (looking back in
time at existing data sets) of the numbers of
cavities in people who chew gum with xylitol
compared to people who don’t chew gum at
all.
b. A meta-analysis (an analysis of a large
number of smaller studies already completed)
of all the studies on xylitol that were
assessing insulin response and weight loss.
c. A double-blinded, placebo-controlled trial
comparing formation of dental carries
(cavities) in subjects who chewed gum with
xylitol each day compared to those
chewing placebo/control gums contain
either sugar or another artificial
sweetener.
d. A survey of dentists regarding their opinions
on the benefits of chewing gum containing
xylitol.
Regarding the claim that xylitol influences dental
health, here are a few arguments that could be made.
Please evaluate them by identifying which logical
fallacy is being used, if any.
4. Xylitol is good for dental health because there is
well-controlled clinical, empirical evidence
supporting the claim.
a. The genetic fallacy
b. The fallacy fallacy
c. False cause
d. The bandwagon fallacy
e. No logical fallacy is being used
5. No one has proved that xylitol isn’t good for
dental health, so therefore it must be.
a. Burden of proof
b. Genetic fallacy
c. Strawman
d. Ad hominem
e. No logical fallacy is being used
Tuesday, 14 Feb 2022
6. Xylitol occurs naturally in very small amounts in
many different types of fruit. It makes a much
better artificial sweetener that other artificial
sweeteners, and is probably good for dental
health, because it’s found in plants.
a. Black and white
b. Tu quoque
c. Special pleading
d. Naturalistic fallacy
e. No logical fallacy is being used
Exobiologists (biologists who research the
possibility of life outside of Earth) work closely with
astronomers to come up with efficient ways to detect
the potential presence of life on other worlds that are
light years away. There are many different
techniques and many different variables that could be
used.
7. RNA is thought to have played an important role
in the evolution of life for which of the following
reasons?
I.
It occurs in enormous quantities
naturally in inorganic materials.
II.
In encodes genetic information that
can be transmitted from generation to
generation.
III.
It can catalyze some cellular
functions.
a. I only
b. II only
c. III only
d. I and II
e. II and III
8. In the formation of the earliest eukaryotic cells,
which of the following components most likely
arose the most recently?
a. DNA genome
b. Plasma membrane
c. Flagellum
d. Mitochondria
BIOL251 – Cell Biology
Exam #1
9. Which of the following macromolecules could
hypothetically yield the most diverse array of
constituent monomers after complete hydrolysis?
a. DNA
b. Glycogen
c. DNA polymerase (a protein)
d. RNA
e. Stearic acid (an 18-carbon fatty acid)
(Role-play) If you were an exobiologist, working for
NASA, and were tasked with analyzing a particularly
interesting meteorite that landed on Earth, how you
go about analyzing it for various biological
macromolecules? See questions below for each type
of macromolecule and choose the most appropriate
analysis technique.
10. Amino acids and proteins
a. Light microscopy
b. Taste it
c. MALDI-TOF-MS
d. HPLC-MS/MS
e. Next generation sequencing (NGS)
11. Lipids
a. Light microscopy
b. Taste it
c. MALDI-TOF-MS
d. HPLC-MS/MS
e. Next generation sequencing (NGS)
12. Carbohydrates
a. Light microscopy
b. Taste it
c. MALDI-TOF-MS
d. HPLC-MS/MS
e. Next generation sequencing (NGS)
Let’s say that you used the correct technique to
analyze the amino acids and proteins and discovered
something incredible: several proteins that are
between 10-100 amino acids long!
Tuesday, 14 Feb 2022
Your first suspicion is that this might be protein
contamination from the landing site or from the
collection team or from the lab.
13. Which of the following would be the most
convincing piece of evidence suggesting that the
proteins came from an extraterrestrial source?
a. The amino acids that make up the
different proteins are a 50:50 mixture of Land D- enantiomers.
b. The proteins are all globular
c. Most of the proteins are glycosylated
d. The proteins are held together with disulfide
bonds
e. Some of the very, very short proteins appear
somewhat similar to ones found on earth
14. If, in your analysis, you discovered that all of the
proteins appear identical to proteins commonly
found in plant life in the landing area as well as
human proteins found in skin cells, but still
argued that while it appears that it’s all
contamination from Earthly sources, but that
some of the proteins are likely from
extraterrestrial life, as a compromise, you would
be committing which logical fallacy?
a. Genetic fallacy
b. Middle ground
c. Texas sharpshooter
d. Ambiguity
e. No logical fallacy is being used
15. There are 3 different lipid bilayers that separate
the interior of the nucleus from the exterior of the
cell. Two of these lipid bilayers are the plasma
membrane and the nuclear envelope. What
organelle’s membrane makes up the third lipid
bilayer?
a. The mitochondrion
b. The Golgi apparatus
c. The peroxisome
d. The rough endoplasmic reticulum
e. The cell wall
16. Which of the following activities supports
getting students to study from their incredibly
BIOL251 – Cell Biology
Exam #1
expensive textbooks and do the heavy-lifting of
learning the material?
a. Dr. Burns lecturing on the terms in the
textbook
b. Providing
extra
credit
points
for
extracurricular activities
c. Students taking weekly quizzes
d. Going over case studies and real-life
examples in class
17. Which of the following is NOT one of the three
core tenets of Scientific Teaching?
a. Alignment
b. Active Learning
c. Diversity
d. Assessment
18. One of the most effective ways of studying
material for class is to:
a. Only work alone
b. Only work in teams
c. Go over the material alone then study with
a team
d. Only look at the material the day before the
exam
b.
c.
d.
e.
Tuesday, 14 Feb 2022
The contents of the lysosome originate in
the smooth ER
The lysosome can fuse with an endosome
The lysosome functions in export packaging
all of the above
Your bones are in a perpetual cycle of being built and
torn apart. There are two different cell types that are
responsible for this remodeling:
Osteoblasts - build up bone mass
Osteoclasts - degrade bone mass
Both of these cells types are active all the time,
though the relative balance of their activities changes
in response to bone damage (like a break), bone
stress (like that generated during exercise), blood
calcium levels, and the influences of a variety of
hormones including osteocalcin, parathyroid
hormone, estrogen, testosterone and others.
Parathyroid hormone (PTH) is secreted by the
(surprise) parathyroid glands in the neck. PTH shifts
the relative activity of the bone-building and bonedegrading cells in favor of breaking down bone and
releasing the calcium stored in the bone material into
the bloodstream.
19. There are only 20 naturally occurring amino
acids.
a. TRUE
b. FALSE
20. DNA is synthesized in the 3’ to 5’ direction in
a. prokaryotes.
b. eukaryotes.
c. archaea.
d. all of the above
e. none of the above
21. RNA is synthesized in the 3’ to 5’ direction in
a. prokaryotes.
b. eukaryotes.
c. archaea.
d. all of the above
e. none of the above
22. Which of the following is true of a lysosome?
a. The lysosome may function in glycosylation
23. Based on the structure shown above, what type
of hormone is PTH?
a. it is likely a protein hormone
b. it is likely a steroid hormone
c. it is likely glycosylated
d. it is likely a very large molecule
e. it is likely a very small molecule
24. What do you predict would be the most effective
means of administration of PTH to a patient,
assuming they needed a dose?
a. Orally in pill form
BIOL251 – Cell Biology
Exam #1
b. Orally as a liquid suspension
c. As a rectal suppository
d. As a dissolvable sublingual tablet (under the
tongue)
e. As a subcutaneous injection (under the
skin)
Tuesday, 14 Feb 2022
“One possible explanation for the limited success of
calcium supplementation is that even when there is
abundant calcium in the body, unless the cells that
add it to bone mass are more active than those that
are removing it from bone mass, there will be very
little improvement, if any.”
Interestingly, only osteoblasts have receptors for
PTH. Once they have been signaled by PTH, the
osteoblasts begin secreting a soluble signaling
protein called RANKL that increases nearby
osteoclast proliferation and activity.
27. Based on the above correct information, which
of the following is a reasonable statement?
a. Boosting the level of calcium in the blood
stream and diet is an effective therapy to
combat osteoporosis.
b. High levels of calcium in the diet and blood
serum are not an effective preventative
measure or therapy for osteoporosis.
25. Denosumab is an FDA approved antibody
protein that binds to and inhibits RANKL. It is
used pharmacologically to treat patients. What
would you guess its typically use case is (what is
it probably used for)?
a. In patients with hypercalcemia (high blood
calcium levels)
b. In patients at risk of hCG disorders
c. In patients at risk for osteoporosis
d. In patients with dangerously high bone
density
e. In patients suffering from eating disorders
26. Osteoporosis, a weakening of skeletal bones due
to decalcification, is more prevalent in older
women than in older men, and typically begins
following menopause. Menopause reduces the
production of the hormone estrogen by the
ovaries. What role would you predict estrogen
has on osteoclast and osteoblast?
a. Estrogen alters the activity of these two
cell types to favor osteoblasts
b. Estrogen alters the activity of these two cell
types to favor osteoclasts
c. Estrogen triggers the release of human
chorionic gonadotropin from the anterior
pituitary gland
d. I predict that it has no role
When there is a strong hormonal program in place
that is altering the activity of bone remodeling cells
to favor those that break-down bone (osteoclasts),
supplementing with high levels of calcium (from
vitamin pills) only has a small effect on slowing or
preventing osteoporosis. With this information in
mind, please evaluate the following:
Dr. Decker of Platonic University has devised a
therapy for osteoporosis that he is sure will work.
After extensive research involving rigorous animal
modeling and human clinical trials, he discovered
that altering the hormone balance can reset the
relative activities of osteoclasts and osteoblasts,
resulting in maintenance of healthy bone structures.
After presenting his findings at the International
Osteoporosis Foundation meeting, he attempted to
answer some questions from the audience. The first
question, posed by an postdoctoral attendee, was,
“How do you know that this works?” To which Dr.
Decker responded, “Hundreds of patients in my
clinical trial had statistically significantly improved
bone density outcomes when compared to patients
who only received placebo treatments in addition to
standard care.” To which the postdoc replied, “I
don’t buy it. There’s no way that can work.”
28. What logical fallacy is present in Dr. Decker’s
postdoctoral questioner?
a. The Texas sharpshooter fallacy
b. The argument from incredulity
c. The bandwagon fallacy
d. The argument from authority
e. The genetic fallacy
BIOL251 – Cell Biology
Exam #1
Tuesday, 14 Feb 2022
gel results
31. If we consider that the top of the gel is where
the samples were loaded in the wells of the gel
(you can see their outlines in the picture at the
left) and the bottom of the gel, logically at the
bottom, when connecting the electrical terminals
to the gel apparatus, where would you want to
connect the positive, red cathode?
a. At the top of the gel
b. At the bottom of the gel
In the agarose gel image above, there are 5 lanes
that have been loaded with sample and run down
the gel. Lane 1 was loaded with a standard that
contains a mixture of double-stranded DNA
fragments of known sizes to use as a “molecular
ruler.”
29. Which lane contains the sample with the
shortest DNA fragment?
a. 2
b. 3
c. 4
d. 5
30. If you added functional groups to a DNA
fragment to make it have a larger-than-usual
negative charge and then ran it on a DNA
electrophoresis gel, what would be different
compared to a run without the addition?
a. The fragment would appear to be larger than
it actually is.
b. The fragment would appear smaller than
it actually is.
c. The fragment would bind to the gel and not
move.
d. The fragment would be detectable without
staining.
e. There would be no discernable change in the
32. If you were to run a PCR reaction, but you
screwed up and the sequence of one of the
primers doesn’t actually match the template
DNA anywhere, while the other primer was OK,
how many copies of the starting template DNA
would you have after 10 cycles of PCR,
assuming you started with one double stranded
copy [this is tricky, but you should be able to
figure it out if you sketch a bit]?
a. 1 copy of each strand
b. 11 copies of each strand
c. 1 copy of one strand and 11 copies of
another
d. 210 copies of both strands