Dr. Reichler’s Bio 301L MWF 9-10am Print
Exam #3 December 6, 2006
Read each question carefully and don’t hesitate to
ask if a question seems unclear. If possible, answer each
question in the space provided, but if needed, continue on the
back. If you use a drawing as part of your answer, be sure to
also include a written explanation. These questions have specific
answers, although for some, more than one answer is possible. To
receive full credit you must clearly and fully answer the question
being asked. This exam is worth 103 points with the points for
each question noted in parentheses.
1. How can telomere length be used to determine someone’s risk of
developing cancer? (8 pts)
Telomeres get shorter by either DNA
damage and/or DNA replication. During DNA replication mutations
occur. The cause of cancer is mutations so telomere shortening by
either DNA damage or during DNA replication will be evidence of an
increased risk of cancer.
2. What are two characteristics that would make a tumor difficult to
treat? (6 pts)
Any two of: MDR
over-production, malignant because the ECM or cell attachment protein
under-production, over production of blood vessel inducing proteins
3. How can an HIV infection increase the chance of skin cancer? (6 pts)
HIV infects T-cells, and the T-cells
are responsible for getting rid of abnormal cells like cancer
cells. As the HIV virus kills T-cells, there are fewer T-cells to
rid the body of abnormal cells.
4. Why are telomeres short in an animal that has been cloned, and why
is this bad for the animal?
Telomeres shorten due to DNA damage
and/or during DNA replication. Older cells will have replicated
many times and/or have some DNA damage. Therefore the cells used
for cloning will have short telomeres. If the telomeres get too
short, the cell cannot divide. So short telomeres may limit an
5. Which cell has more methylated DNA, a totipotent cell or a
pluripotent cell? Why? (8 pts)
A pluripotent cell has more
methylated DNA. Totipotent cells can become any type of cell, but
a pluripotent cell can become only certain types of cells. The
limit in the pluripotent cell is that some genes are methylated and
their expression is suppressed.
6. What are two instances when a virus cannot be detected by
B-cells? Explain. (8 pts)
During the lysogenic phase it has
inserted its DNA into the host cell DNA, and when it is replicating
inside a cell. B-cells can only recognize foreign particles
outside the cell, so in both instances it is inside the cell and
therefore undetectable by B-cells.
7. Are stomach acids needed in the stomach even when no food is
present? Why or why not? (6 pts)
Yes, to kill pathogens that are
filtered in the nose and throat by cilia, and then swallowed into the
8. What stimulus could a human respond to that would not involve
neurons? (6 pts)
(Very few people answered this
question correctly, and so it was not graded, and the grades were
calculated out of 94 points.)
Infection by a pathogen. The
immune system recognizes the foreign object, but does not require
activation of neurons.
9. Does a neuron use more energy at rest or when transmitting a
signal? Why? (6 pts)
At rest pumps that use ATP are needed
to maintain the separation of positive charges outside the neuron.
10. If you blocked the release of neurotransmitters from the rods in
your eye, would you perceive that as light or dark? Why? (8 pts)
Light. Rods secrete an
inhibitory neurotransmitter. The absence of this inhibition
activates the subsequent neurons and is perceived as light.
11. What would happen in a muscle cell without tropomyosin? (8 pts)
It would remain contracted. The
myosin and actin would be locked together, and the sarcomere would be
12. What two nutrients would you want to eat to ensure effective muscle
movement? Describe why each one is important for muscle movement.
Any two of: calcium- to
activate muscle contraction by binding to tropomyosin. Amino
acids- for the production of the muscle proteins actin, myosin,
and tropomyosin. Sugars, fats, proteins- to produce the ATP
needed for muscle contraction. Na+/K+- for neuron signaling to
activate the muscle.
13. What would be unusual about an animal with very sharp teeth and a
long digestive system? (8 pts)
Sharp teeth usually indicate a
carnivore that needs to catch and hold prey, and a long digestive
system is usually indicative of a herbivore that needs the longer
digestive system to extract the nutrients from the harder to digest
14. Would the specific immune system be able to kill a pathogen in your
small intestine? Why or why not? (8 pts)
No, the small intestine is outside
the body and the blood where B-cells and T-cells circulate does not
come into contact with the inside of the small intestine.
Bonus: What evidence suggests that the effects of birth season on
exam scores do not occur during the first few weeks of fetal
development? (3 pts)
The correlation between birthday and
exam scores is different in males and females, but during the first few
weeks of development all human fetuses are developing as females.
So if the effect occurs during the first few weeks, it should be the
same in both sexes.