Fall 1996 Biology 111 Exam #1 - Cellular Communications


There is no time limit on this test, though I have tried to design one that you should be able to complete within 2.5 hours, except for typing. You are not allowed to use your notes, old tests, or any books, nor are you allowed to discuss the test with anyone until all exams are turned in at 10:30 am on Monday September 22. EXAMS ARE DUE AT CLASS TIME ON MONDAY SEPTEMBER 22. You may use a calculator and/or ruler. The answers to the questions must be typed on a separate sheet of paper unless the question specifically says to write the answer in the space provided. If you do not write your answers on the appropriate pages, I may not find them unless you have indicated where the answers are.



Please do not write or type your name on any page other than this cover page. Staple all your pages (INCLUDING THE TEST PAGES) together when finished with the exam.

Name (please print):




Write out the full pledge and sign:







How long did this exam take you to complete (excluding typing)?




Lab Questions:

3 pts.
1) What is the percent solution (w/v) of a substance (called Tris) that is 1.35 M and has a molecular weight of 121? For full credit, show how you calculated your answer.

121 X 1.35 = 163.3 g/L

163.3 g /1000 mL

16.3 g / 100 mL = 16.3%


5 pts.
2) Which line (A, B or C) on the graph below depicts the enzyme reaction with the greatest activity? You must explain your answer to receive full credit. The only variable that was changed between A, B and C was the amount of enzyme in the reaction.



C is the reaction with the greatest activity because you can see that the initial slope is the greatest, and as all of the substrate is consumed, the line levels off. This consumption of substrate only happens in reaction C.

2 pts.
3) What roles do isocitrate and NADP+ play in the reaction of IDH?

Isocitrate is the substrate and NADP+ is the coenzyme.

Lecture Questions:

8 pts.
4) List the four fundamental components in evolution.

There is genetic variation in the population.
The population tends to over reproduce which leads to a struggle to survive.
During this struggle, those with a selective advantage will survive and be able to reproduce.
The next generation will inherit the traits that advantageous.

6 pts.
5) List three functions of the endoplasmic reticulum.

There are many, including: the synthesis of lipids, the production of proteins that will be inside organelles or secreted, and the storage of calcium ions.

10 pts.
6) List five different modulating molecules (i.e. modulators) that we have studied so far. For each example you give, explain what molecule is being modified and how its function is changed by this modification.

Again, there are many to choose from, including:
1) cAMP modulates cAMP dependent protein kinase by activating the kinase;
2) acetylcholine modulated the acetylcholine receptor to open the gate and allow Na+ ions to flood into the muscle cell;
3) phosphorylation is a covalent modulator that affects many proteins, including the calcium ions in the cardiac muscle so that they stay open longer (in response to fear).

10 pts.
7) Describe the similarities and differences between ion channels and ion pumps.

Similarities include: both allow ions to cross a membrane; both are integral membrane proteins.
Differences include: channels are selective for ions while pumps are specific; channels do not use ATP to transport the ions while pumps do; channels allow many more ions through per second than do pumps; channels allow ions to go down their concentration gradient while pumps work against the gradient.

10 pts.
8) Describe the steps involved in muscle contraction as myosin goes through its cycle. Restrict your answer to the role played by myosin and do not discuss any other protein except actin.

1) The myosin head is has been phosphorylated and is waiting to bind an action binding site (calcium required to initiate this).
2) The phosphorylated myosin head binds to actin. This causes the myosin head to change its shape.
3) The change in shape causes the phosphate to fall off. This causes the myosin to change its shape.
4) The myosin bends and pulls actin along with it. The myosin head has changed shape so that it can bind ATP.
5) Myosin must bind ATP in order to release the actin. This allows the head to be phosphorylated again and the cylce repeats.

8 pts.
9) We have seen calcium used a number of times in cellular communications. List and briefly describe four examples of how it is used in different situations to facilitate different actions. There are several possible answers but here are 4:

Calcium is used to initiate muscle contraction by indirectly revealing the actin binding site.
Calcium is used in nerve termini to facilitate the exocytosis of neurotransmitter.
Calcium is used in a fertilized egg to facilitate exocytosis and provide the slow block to polyspermy.
Calcium is also used in the egg to activate it and begin mitosis.

10 pts.
10) a) Define the term "membrane potential". The separation of charges across a membrane.

b) What protein is responsible for establishing the resting membrane potential? Na+/K+ pump

c) What is the numerical value associated with the resting membrane potential of a myocyte? -70 mV

d) What role, if any, does calcium play in generating the membrane potential? none

e) Excluding calcium from consideration, what ions are responsible for establishing the membrane potential? sodium and potassium


8 pts.
11) a) What is phosphotidylinositol bisphosphate? It is a phospholipid.

b) What protein is activated to cleave it into two parts? phospholipase C

c) What two parts are produced (give both the abbreviations and the full names)? inositol triphosphate (IP3) and diacylglycerol (DAG)


6 pts.
12) A new gene has been discovered (LQT1) in humans that causes long-QT syndrome (a heart beat irregularity). The gene encodes an ion channel and people with this disease do not produce this channel. If you were the coroner, how could you determine if this were the cause of death? Choose a method that we have covered and explain what you would expect to see if this were the cause. What control would you want to include with your experiment?

I was thinking that the coroner might want to use either gel electrophoresis or better yet, immunofluorescent labeling of the channel. The coroner could take a small sample of tissue, slice it thin, and then use a labeled antibody against this ion channel and see if the channel were present. As a control, one would want to examine a healthy heart sample as well.

6 pts.
13) What does gel electrophoresis allow a researcher to do? This allows the researcher to separate molecules based on their molecular weight (size). One can also compare how much of each molecule is there in multiple samples.

8 pts.
14) What does each of the following enzymes do when each is activated? Make sure you include the substrate and product in your answer.

a) glycogen phosphorylase - cleaves glycogen into glucose-1-phosphate (glucose)

b) adenylyl cyclase - converts ATP into cAMP

c) G protein - converts GTP into GDP or activated the next enzyme in a cascade, like protein kinase C

d) phosphorylase kinase - phosphorylates glycogen synthase (slows it down) and glycogen phosphorylase (speeds it up)

Reutrn to the Biology 111 Page.