Cell Biology Exam #2-Spring 2000

 

Name___________________    Lab section__________________

Multiple choice.  Choose the best answer (2 points each).

1.__C___ Which of the following cell parts does not arise from vesicles of the E.R.?  a) lysosomes; b) Golgi apparatus; c) cytoskeleton; d) vacuoles; e) nuclear membrane

2.___C__ Microtubules and microfilaments are involved in all of the following processes except:  a) movement of organelles through the cytoplasm of the cell; b) separation of chromosomes on the spindle fibers; c) protein synthesis; d) movement of cells by cilia or flagella.

3.____D_ Which of the following is least associated with membrane bound ribosomes: a) secreted proteins; b) protein synthesis; c) rough E. R.; d) lipid synthesis.

4.___B__ A cell that produced a lot of secreted glycoproteins would be expected to have more of this type of organelle than a cell that did not secrete any glycoproteins:  a) nucleus; b) Golgi apparatus; c) lysosomes;  d) mitochondria; e) chloroplasts.

5.___A__ Which one of the following structures is directly involved in the direct passage of electrical signals between cells as, for example, in the vertebrate heart?  a) gap junctions  b) desmosomes  c) tight junctions  d) plasmodsemata

6.____B_ If a cell lacked ribosomes, it would not be able to
a)  form a spindle apparatus.  b)  synthesize proteins.  c)  respire.  d)  hydrolyze fat.
e)  form a Golgi vesicle.

7. ___C__A cell is exposed to a substance that prevents it from dividing. The cell becomes larger and larger. This situation
a) should present no problem to the cell since it can continue to perform all other necessary functions
b) should present no problem to the cell because the surface area of the cell will increase as the volume of the cell increases
c) will eventually be problematic since the cell's ability to absorb nutrients through its outer membrane will not keep pace with increasing cytoplasmic needs
d) should be beneficial since the cell will be able to divert the ATP normally used for cell division to other processes
e) both a and b

8. ___E__Resolving power:
a) is the ability of an optical instrument to show two objects as separate.
b) is the measure of an image's clarity.  c) is the ability of an optical instrument to magnify an image.  d) is the ability of an optical instrument to estimate the size of an image.  e) both a and b
 
9.___D__A child is hospitalized for a series of chronic bacterial infections and dies despite heroic efforts. At autopsy, the physicians are startled to see that the child's white blood cells are loaded with vacuoles containing intact bacteria. Which of the following explanations could account for this finding?
a) A defect in the Golgi apparatus prevented the cells from processing and excreting the bacteria.
b) A defect in rough endoplasmic reticulum prevented the synthesis of the antibodies (defensive proteins) that would have inactivated the bacteria.
c) A defect in the cell walls of the white blood cells permitted bacteria to enter the cells.
d) A defect in the lysosomes of the white blood cells prevented the cells from destroying engulfed bacteria.
e) A defect in the surface receptors of the white blood cells permitted bacteria to enter the cells.

10. ___D__The accumulation by active transport of large amounts of solutes in a plant's water vacuole helps to keep:  a) the environment hypertonic compared to the inside of the plant cell; b) the plant cell plasmolyzed; c) the plant cell from having too much excess ATP; d) the plant from wilting.

11.___E__ Receptor mediated endocytosis:  a) is a form of active transport; b) is a form of facilitated diffusion; c)describes the method by which vacuoles from the ER fuse to the membranes of the Golgi apparatus ; d) is a specialized type of exocytosis; e) is a way to transport specific substances from the environment in to the cell.

12.___A__ According to the fluid-mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?  a) they move laterally (side to side) along the plane of the membrane; b) they frequently flip-flop from one side of the membrane to the other; c) they occur as an uninterrupted bilayer with membrane proteins restricted to the surface of the membrane; d) they have hydrophilic tails in the interior of the membrane.

13.___C__ Which of the following would most likely be the function of a peripheral membrane protein located on the cytoplasmic side of the cell membrane?
a) cell-cell recognition; b) hormone receptor; c) anchorage of the cell membrane to the cell's cytoskeleton; d) carrier molecule.

14.___C___The main problem with the Davson-Danielli model of membrane structure was that it:  a) did not account for the phospholipid bilayer  b) phospholipid fluidity was impossible  c) it placed membrane proteins in a layer on the membrane surface  d) early electron micrographs clearly did not support this model  e) nothing is wrong with the model, and it is accepted today by cell biologists

15..___E__The first scientist (s) to propose that cell membranes are phospholipid bilayers.a) H. Davson and J. Danielli b) I. Langmuir c) C. Overton d) S. Singer and G. Nicolson  e) E. Gorter and F. Grendel
 
16.___A__Small, nonpolar, hydrophobic molecules such as fatty acids
a) easily pass through a membrane's lipid bilayer  b) very slowly diffuse through a membrane's lipid bilayer  c) require transport proteins in order to pass through a membrane's lipid bilayer d) are actively transported across cell membranes
e) enter the cell via endocytosis

17.___B__Some protozoans have special organelles called contractile vacuoles that continually eliminate excess water from the cell. The presence of these organelles tells you that the environment :  a) is isotonic to the protozoan  b) is hypotonic to the protozoan  c) is hypertonic to the protozoan  d) contains a higher concentration of solutes than the protozoan  e) both c and d

18.____E_If placed in tap water, an animal cell will undergo lysis whereas a plant cell will not. What accounts for this difference?
a) expulsion of water by the plant cell's central vacuole   b) the relative impermeability of the plant cell membrane to water  c) the relative impermeability of the plant cell wall to water d) the fact that plant cells are isotonic to tapwater  e) the relative inelasticity and strength of the plant cell wall

19.___B__Which of the following about substrate-level phosphorylation is false:
a) it involves an enzymatic transfer of phosphate groups; b) it requires membranes in order to occur; c) an organic molecules is the source of the high energy phosphate that is donated to ADP; d) it does not occur during the operation of the electron transport system.

20.____A______ All of the following reactions occur in the mitochondria except:
a) conversion of pyruvate to ethanol; b) conversion of pyruvate to acetyl Co-A; c) TCA cycle; d) the electron transport system; e) chemiosmotic oxidative phosphorylation.

21.___B___ The electrons released by FADH2 during its oxidation to FAD by the electron transport system finally end up as part of this molecule: a) glucose; b) water; c) carbon dioxide; d) ATP e) NAD+

22___A__ A mutant protist is found in which some mitochondria lack an inner mitochondrial membrane. Which of the following pathways would be completely disrupted in these mitochondria?
a) chemiosmosis    b) alcoholic fermentation   c) the Krebs cycle   d) glycolysis   e) both c and d

23.___D__Which of the following coenzymes would have to be continually present in the cell in order for the oxidation reactions of glycolysis to occur?
a)  FADH2; b) NADH ; c) ATP; d) NAD+; e) all of the above.
 
 

24.____E______ During chemiosmosis,
a) energy is generated because H+ ions move freely across the phospholipid bilayer of the mitochondrial membranes  b) ATP is synthesized when H+ ions move through a channel protein (ATP ase) in the inner membrane   c) energy is generated by coupling endergonic  reactions with other exergonic reactions  d) a concentration gradient is generated when large numbers of H+ ions are passively transported from the matrix of the mitochondrion to the mitochondrion's intermembrane space    e) both b and c

25.___C__   The conversion of pyruvate into lactic acid in human cells during fermentation occurs for the same fundamental purpose that this set of reactions takes place:  a) glycolysis; b) TCA cycle; c) electron transport system; d) decarboxylation  e)feedback inhibition

26.__D___ Which of these processes may occur in the cytoplasm of an animal cell:
a) chemiosmotic ATP synthesis; b) the electron transport system; c) the TCA cycle; d) substrate level phosphorylation; e) all of the above.

27.___D__ The greatest percentage of the total amount of ATP produced by the aerobic respiration of 1 glucose molecule is produced by this system:
a) glycolysis; b) fermentation; c) TCA cycle; d) the electron transport system.

28.___C__ 8 molecules of NADH  are produced per glucose molecule during this process:  a) fermentation; b) the electron transport system; c) the Kreb's cycle; d) glycolysis;
e) a & d.

29. (6 points)  What is the purpose of cell fractionation?  How is cell fractionation accomplished?  What role does differential centrifugation play in this process?

The purpose is to separate cell organelles for further study and characterization.  Cell fractionation involves two steps:  1) homogenization-breaking open the cell in such a way that the organelles are not destroyed  2) separation-This is accomplished by differential centrifugation.  This technique separates organelles in a centrifuge tube based upon difference in the organelleís densities.  The more dense the organelle, the faster it moves to the bottom of the tube at a given speed.
 
 

30. (4 points) Referring to the concept of conformational change, describe how the hydrolysis of ATP is coupled to the operation of the NA+/K+ pump.  You do not have to describe the complete cycle of events relating to the operation of the pump.  Just concentrate on those events of the cycle (remember the diagram from your book) illustrating the operation of the Na+/K+ pump) that are the direct result of the hydrolysis of ATP.
 
 

When ATP is hydrolyzed, the released phosphate attaches to (phosphorylates) the Na+/K+ Atpase pump.  This phosphorylation causes a conformational change that has the following effects:  1) the carrier opens to the outside (it wa previously open to the inside)  2) the shape of the Na+ binding sites change so that Na+ can no longer bond  3) the shape of the K+ binding sites change so that K+ can now bind (the shape of these sites was previously incorrect and could not bind K+).
 

31. (4 points) What would be the effect on the cellís endomembrane system if you gave the cell a drug that inhibited the process of endocytosis but not the process of exocytosis?  Explain.

All of the membranes of the endomembrane system would eventually become part of the plasma membrane (the endomembrane system would disappear).  Membranes would be lost from the system by exocytosis but not returned to the system by endocytosis.  In order for the endomembrane system and the plasma membrane to maintain their normal size, there has to be an equilibrium between the rates of exocytosis and endocytosis.
 

32. (3 points each) Agree or disagree with the following statements.  In either case, fully defend your answer.

A. Proteins secreted from a cell (insulin being secreted from pancreas cells) are produced  on 80 S ribosomes while proteins that are not secreted from the cell (they remain in the cytoplasm) are synthesized on 70 s ribosomes.

Disagree-Both types of proteins are made on 80s ribosomes.  Secreted proteins are made on 80s membrane bound ribosomes and non secreted proteins are made on 80s free ribosomes.  70 s ribosomes are prokaryotic ribosomes  (these are also found in the mitochondria of a cell but that organelle does not secrete proteins).
 

 
B. The fact that plants actively transport solutes from the soil into their root cells helps to compensate for the fact that plant cells lack an internal skeleton to provide body support.

Agree-This makes the plant root cells hypertonic compared to the soil solution.  Thus water will enter the root cells and keep the cells turgid.  The turgidity of the cells is what gives the tissue support in the absence of an internal skeleton (when the cells lose their turgidity, the tissue wilts).
 

C. The electron transport cannot function unless molecular oxygen (O2) is available to serve as a final electron acceptor.

Disagree-although the electron transport system does need a final electron acceptor that it obtains from the environment, this acceptor does not have to be O2.  Cells that can anaerobically respire (facultative anaerobes) can use terminal electron acceptors other than O2  (such as nitrate).
 

D. The process of cellular respiration has another important function in metabolism in addition to its role of completely oxidizing food molecules to produce energy.

Agree-The catabolic role of respiration is dedicated to producing the maximum amount of ATP.  However, when energy demands are not high, there is an anabolic role to respiration.  This involves producing carbon skeletons (partial breakdown products of respiration pathways)  for the biosynthesis of other organic molecules (converting acetyl-CO-A into fatty acids for lipid synthesis)

 
33. (4 points) Explain how the oxidation of NADH2 and FADH2 by the electron transport system results in the development of an H+ gradient across the inner membrane of the mitochondria.

The oxidation of reduced coenzymes by the ETS is an exergonic process that is used to drive the development of an H+ gradient across the inner membrane of the mitochondria.  The gradient (high H+ in the intermembrane space and low H+ in the matrix) builds up because of three factors: 1) the inner membrane is impermeable to H+  2) some of the ets carriers are hydrogen only carriers while others are electron only carriers   3) these two types of carriers are assymetrically distributed within the inner membrane (electron only carriers facing the intermmebrane space side and hydrogen only carriers facing the matrix side).
 

34. (4 points) Based upon your knowledge of the basic differences between fermentation and aerobic respiration, explain why aerobic respiration of glucose is so much more efficient  at  producing ATP compared to fermentation. You don't have to describe both processes in detail to answer this question, just indicate how the basic differences in the two processes account for the large difference in efficiency of ATP production.

Aerobic respiration has two pathways that fermentation does not (the Krebís cycle and the ETS).  The Krebís cycle finishes the oxidation of pyruvate and produces 8 NADH and one FADH2 per glucose.  These molecules represent potential energy.  The Krebís cycle also produces 2 ATP/glucose by substrate level phosphorylation.  The ETS is the system used for recylcing the reduced coenzymes in aerobic respiration.  This system produces an H+ gradient as it recycles coenzymes and this H+ gradient is the sources of  32ATP/glucose.  The recycling step that fermentation uses does not generate an H+ gradient and, thus, no additional ATP besides what is produced by substrate level phosphorylation in glycolysis.