C2006/F2402 '02 -- Review Questions for Exam #3 = Questions from exams 2 & 3 of last year

1. Supposed that proteins P and Q are both made in liver cells. Protein P is a tyrosine kinase receptor. Protein Q is a G-protein linked receptor.

    A. Which protein(s) should be made on ribosomes attached to the ER? (protein P) (protein Q) (both) (neither) (either one or both -- canít predict).

    B. Which protein(s) should have more than one cytoplasmic domain? (protein P) (protein Q) (both) (neither) (either one or both -- canít predict).

    C. Suppose the receptors bind to their respective ligands. Which binding is more likely to trigger an alteration in the state of activation of protein kinase A? (protein P) (protein Q) (either one -- both are equally likely) (neither -- neither of these receptors could trigger this response) AND which binding is capable of generating a second messenger? (protein P) (protein Q) (both) (neither). Explain briefly.

2. Consider the following choices: (Tyrosine kinase) (Protein Kinase A) (Protein Kinase C) (cyclin dependent kinase) (MAP Kinase) (all of these) (none of these). For parts A-D, pick a choice and provide one sentence of back up information.

    A. A G-protein that activates a phospholipase is most likely to lead to activation of ___________________.

    B. Which of these proteins is unstable (or combines with a subunit that is unstable)? ____________________.

    C. Which of these proteins is most likely to be regulated by receptor mediated endocytosis? ______________.

    D. The transition from G2 to mitosis requires the activation of _____________________.

    E. A single type of growth factor, binding to a single type of receptor, should be able to activate _________________________ (Fill in one or more choices for this one -- include all proteins listed that will be activated in the absence of additional transcription). Explain briefly.

3. Consider the following 3 possible mutations.

(1) Adapter protein is inactive. Normal adapter protein binds to activated TK receptor and to Ras.

(2). Ras is constitutively activated.

(3). MEK (MAPK-kinase) is inactive.

For each part of this question, circle one or more answers and explain.

    A. Which of the mutations listed could cause loss of growth control (uncontrolled division)? (1) (2) (3) (none). Explain why each one will or will not cause loss of control.

    B. Consider the normal forms of the genes for the adapter protein, ras, and MEK. Which of these genes  -- in their normal, un-mutated form -- should be considered proto-oncogenes? (Ras) (MEK) (adapter protein gene) (none) AND which of the genes listed should be considered tumor suppressors? ? (Ras) (MEK) (adapter protein gene) (none).

    C. Which of the following combinations would cause loss of growth control? (1+2) (2+3) (1+3) (none). Explain why each combo listed will or will not cause loss of control.

    4. (22 pts). The cells on the ventral side of the neural tube are known as floor plate cells. (See bottom of handout 16B. Ventral = bottom side of diagrams. Floor plate = cells in middle section of ventral/bottom side of neural tube = cells from about 5 o'clock  to 7 o'clock. ) Some cells on the ventral side of the neural tube normally become motor neurons. (These are the cells of neural tube on either side of the floor plate = cells at 4 o'clock and at 8 o'clock.)  If a section of floor plate from a second embryo is placed outside the neural tube, the neural tube cells near the added floor plate become motor neurons. If a section of floor plate is placed near any other structure in the embryo, no additional motor neurons form. Base your answers on these results. (Note: on the actual exam, there was a picture.)

    A. The differentiation of motor neurons is best described as an example of (determination) (embryonic induction) (gastrulation) (mosaic development) (regulative development) (transdetermination) (metamorphosis). Circle all terms that apply.

    B. Suppose that a single type of secreted protein and a single type of receptor are required for differentiation of motor neurons.
    B-1. Which cell type is most likely to be synthesizing the secreted protein? (neural crest) (floor plate) (all neural tube cells other than floor plate) (neural tube cells near the floor plate) (epidermis) (some other cell type) (any of those listed are equally likely).

    B-2. Which cell type is most likely to contain the receptor? ________________________ (same choices) AND the receptor should be (on the cell surface) (inside the cell) (either way). Explain briefly how you arrived at your answers.

    C. Suppose gene ess codes for the secreted protein described in part B that is needed for motor neuron differentiation. (Assume the protein has no other function.) Gene ess has 2 alleles, S and s. Allele S codes for a normal protein. Allele s codes for a protein that works at 25 deg. C but is irreversibly inactivated at 37 deg. C.

You have zygotes with the ss genotype. If you let them develop at 25 C until adulthood they have a normal phenotype. If you let them develop at 37 C they are abnormal. You try the following 2 experiments with ss organisms:
    (1) You grow them at 25 C until the end of gastrulation; then shift temperature to 37 C.
    (2) You grow them at 37 C until the end of gastrulation; then shift temperature to 25 C.

    C-1. Which experiment will probably produce an adult with normal motor neurons? (1) (2) (both) (neither).

    C-2. Given your answer to C-1, what should happen in normal SS embryos? The product of gene ess should be made (before gastrulation) (after gastrulation) (either way) AND gene ess should be transcribed in (floor plate cells) (cells that will become motor neurons) (both) (neither) AND the product of gene ess should be active (before gastrulation) (after gastrulation) (either way).
    Explain how the activity of gene ess and its product would produce these results. (If you can think of more than one way these experiments could come out, pick one. Then be sure all your answers are consistent, and explain your reasoning for this one case.)

Following questions are Multiple choice: 3 points each, no explanations.

5. An action potential has just occurred in a neuron, and the membrane is hyperpolarized. At this point, the concentration of K+ inside the cell is ____ the concentration of K+ in the fluid that surrounds the cell.

    a. higher than     b. lower than     c. equal to

6. The refractory period occurs in a neuron because of the time needed for

a. a neurotransmitter to diffuse across the synaptic cleft.
b. the Na/K pump to restore the membrane potential to resting
c. the voltage-gated Na channels to open
d. the voltage-gated K channels to open
e. the voltage-gated Na channels to return to the closed state

7. The equilibrium potential for an ion refers to

  1. the membrane potential that occurs when the ion concentration is equal on both sides of the membrane.
  2. the electrical charge that is needed to balance the concentration gradient of that ion across the membrane.
  3. the proportion of the membrane potential that is due to that particular ion.
  4. the potential that occurs when permeability to Na equals permeability to K.
  5. the potential at the peak of the action potential, when the rate of incoming ions equals that of outgoing ions.

8. A cell is made more permeable to sodium ions. As a result, the equilibrium potential for Na should

  1. become more positive b. become more negative c. not change

9. South America Indians used a kind of tree sap to produce a toxin called woorali, which they would spread over tips of their arrows. An animal shot with the poisonous arrow would be quickly paralyzed. European explorers brought this toxin to Claude Bernard, who sought to discover the mechanism by which woorali acts. He tied a string around the left leg of a frog, which stopped the flow of blood to the left leg, (but the cells could survive normally for the duration of this study). He then injected woorali into the frog, and it was carried by the blood to all parts except for the left leg. Next, he used an electrode to stimulate the nerves leading to the leg muscles. The nerves were stimulated where they exited the spinal cord, above the string, so both the left adn right nerves there had been exposed to woorali. When he stimulated the left nerve, the left leg muscle did contract. When he stimulated the right nerve, the right leg muscle did not contract.

Considering these results, and what you know about membrane proteins, you could conclude that woorali inhibited (voltage-gated channels) (ligand-gated channels) (mechanically-gated channels) (leak channels) (DHP or ryanodine receptors) which allowed the passage of (Na+) (K+) (Ca++). Explain. Your explanation should include which type(s) of channels may possibly have been affected, and which type(s) of channels could not have been affected by woorali. (13)

10. The all-or-none principle of nerve action states that

  1. The action potential moves all the way down the axon, or not at all.
  2. The action potential is produced in all the dendrites of a neuron, or none at all
  3. The action potential always reaches a certain potential, or doesnít occur at all
  4. At one point in the action potential, the channels for all types of ions are open, and another point, the channels for none of the ions are open.

11. A neuron and its attached muscle is placed in a fluid in which Ca++ has been replaced by a different divalent cation (X++). This will make it harder to

  1. generate an action potential when the neuron is stimulated with electrical current
  2. get neurotransmitter release when the neuron is stimulated with electrical current
  3. get muscle contraction when the muscle is stimulated with electrical current
  4. a and b e. a and c f. b and c g. a and b and c

12. When the sarcomeres in a muscle are at their shortest possible length, you would expect to find the t-tubules are

    1. at resting potential     b. hyperpolarized     c. depolarized

13. Myoglobin is a protein that binds oxygen. Based on the spelling of the word, you could assume that myoglobin stores oxygen in

  1. mitochondria     b. glands     c. muscle     d. the CNS     e. Schwann cells and oligodendrocytes

14. When HIV infects the brain, it can lead to the death of brain neurons as a result of paracrine signals released from

  1. Glial cells
  2. Motor neurons
  3. Parasympathetic ganglia
  4. Sympathetic ganglia
  5. Sensory neurons

15. Prior to secretion of ______ an action potential develops in the cell that secretes it.

16. When we eat other animal species, we generally eat their skeletal muscles, though sometimes we eat other organs, such as the brain. Which food would be higher in protein? Higher in fat? Explain. Your answer should indicate the specific types and locations of the protein and fat in the brain and muscle cells. (8)

17. "Not poppy, nor mandragora, nor all the drowsy syrups in the world shall ever medicine thee to that sweet sleep which thou ouídst yesterday", said Iago, suggesting that thereís no drug that would ever again let Othello get a good nightís sleep. The poppy and mandrake plants have long been known to contain compounds that could put a person to sleep, but only recently have scientists discovered the receptors that are stimulated by these compounds, called opiates. There are 3 such receptors. When stimulated, mu receptors leads to opening of K+ channels, lambda receptors leads to inhibition of adenyl cyclase, and kappa receptors leads to closing of Ca++ channels.

    A. Stimulation of which receptor is most likely to cause an IPSP? Explain briefly. (4)

No explanation for these:

    B. After opiates are used repeatedly, the postsynaptic cell often requires a greater than normal stimulus to respond. This is most likely due to (down-regulation of opiate receptors) (up-regulation of opiate receptors) (lengthening of the relative refractory period) (lengthening of the absolute refractory period) . (2)

    C. Sometimes one neuron, say A, sends axon terminals that form a synapse on another neuron, say B, but instead of synapsing on B's cell body or dendrites, neuron A synapses on B's axon, just near the axon terminal. Suppose A synapses on B's axon and B then synapses on C's cell body. (On the actual exam, there was a picture, which you can try to recreate from the information given here.) When A is stimulated, there is a decrease in EPSP's measured on the membrane of C's cell body. The opiate receptor at C is likely to be (mu) (lambda) (kappa). (2)

    D. The finding that humans have receptors for a plant compound suggests that there may be some molecule normally produced by humans which is the natural ligand for this receptor. The natural ligands are called endorphins, and are cleaved from POMC, the pre-prohormone for ACTH. Endorphins must be synthesized in the (dendrites) (cell body) (axon) (axon terminal) of the neuron that releases them. (2)