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
7. ___C__A cell is exposed to a substance that prevents it from dividing.
The cell becomes larger and larger. This situation
8. ___E__Resolving power:
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
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
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?
19.___B__Which of the following about substrate-level phosphorylation is
20.____A______ All of the following reactions occur in the mitochondria
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?
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
24.____E______ During chemiosmosis,
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
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:
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;
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
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).
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
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)
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