Dr. Reichler’s Bio 301L   MWF 9-10am    Print Name:___________KEY__________
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 (angiogenesis),

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?
(6 pts)
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 animals lifespan.

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 stomach.

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 pulled together.

12. What two nutrients would you want to eat to ensure effective muscle movement?  Describe why each one is important for muscle movement. (8 pts)
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 plant material.

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.