BIOL2210: Introductory Cell Biology Sample Midterm Examination

Transcription

1 Name: Student ID#: BIOL2210: Introductory Cell Biology Sample Midterm Examination Total marks: 65 Total time: 75 minutes 1. PRINT your name and student number in the spaces provided at the top left corner of this page AND on the Test Scoring Answer Sheet. 2. This examination consists of three parts numbered Section A, B, and C. Please attempt ALL questions. 3. Section A will be answered IN PENCIL on the provided Test Scoring Answer Sheet. ONLY Test Scoring Answer Sheets will be marked for Section A. 4. Sections B and C will be answered in the spaces provided on the question paper itself. Questions answered in pencil will not be considered for re-marking. Please do not use red ink. Section B Marks Section C Total for B and C

2 Section A Select the BEST answer to the question provided and mark it on your Test Score Answering Sheet. A correct answer is worth one mark. Section A is worth a total of 25 marks. 1. Which of the following scientists was responsible for proposing the third tenet of the Cell Theory? a) Robert Brown b) Matthias Schleiden c) Rudolf Virchow d) Theodor Schwann e) Louis Pasteur 2. Why are most cells small in size? a) In order to maximize surface area-to-volume ratio for exchange between the cell and its environment. b) In order to maintain an efficient diffusion rate within the cytoplasm. c) In order to maintain essential concentrations of compounds needed for various processes within the cell. d) All of the above e) None of the above 3. The high concentration of Na + outside a eukaryotic cell, relative to the interior, is maintained by a) passive diffusion. b) a facilitative transporter. c) a voltage-gated channel. d) a ligand-gated channel. e) direct active transport. 4. How does a deficiency in vitamin C affect the cell? a) It results in the synthesis of defective collagen α-chains which fail to form a stable triple helix. b) It causes excessive hydrogen bonding between hydroxyl groups of proline and lysine, resulting in decreased tissue elasticity. c) It leads to increased interactions between collagen and elastin, resulting in decreased tissue elasticity. d) It prevents the removal of the C and N terminal amino acids from procollagen by procollagen peptidase. e) None of the above.

3 5. The polarity of an individual microfilament can be demonstrated by "decorating" it with this molecule and then viewing the microfilament using electron microscopy. a) F-actin b) S1 myosin fragment c) talin d) α-actinin e) more than one of the above 6. Which of the following characteristics is shared by prokaryotes and eukaryotes? a) The presence of a nucleus b) The presence of mitochondria c) Extensive RNA processing d) The presence of ribosomes e) None of the above 7. In sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), individual proteins migrate in the electric field at rates determined by their a) density b) size c) charge d) shape e) more than one of the above 8. Which of the following compounds could be composed of fatty acyl chains, a glycerol backbone, a phosphate group and inositol. a) phospholipid b) sphingolipid c) glycophosphatidylinositol (GPI)-anchored protein d) sterol e) glycolipid 9. Which class of integral membrane proteins join cells of similar type to one another? a) laminins b) vinculins c) integrins d) collagens e) cadherins

4 10. During the synthesis of cellulose microfibrils, the coordinated movements of cellulose synthase complexes in the plane of the plasma membrane are directed by a) microfilaments. b) intermediate filaments. c) hemicellulose. d) spectrin. e) microtubules. 11. Which of the following types of microscopy relies on the ability of a molecule to absorb light at one wavelength and emit photons of a longer wavelength? a) brightfield microscopy b) phase contrast microscopy c) confocal laser-scanning microscopy d) transmission electron microscopy e) more than one of the above 12. Which of the following scientists first proposed that the plasma membrane of a cell is composed of a lipid bilayer? a) Gorter and Grendal b) Davson and Danielli c) Robertson d) Singer and Nicholson e) Overton 13. Which of the following structures help to form the blood-brain barrier by restricting the movement of extracellular material between adjacent cells? a) gap junctions b) tight junctions c) desmosomes d) focal adhesions e) adherens junctions 14. Where would you most likely find cellulose macrofibrils arranged in different layers oriented at different angles? a) cytoplasm b) primary cell wall c) middle lamella d) secondary cell wall e) basal membrane

5 15. These are fluid-filled, membrane-bound spherical vesicles surrounded by a single, continuous lipid bilayer, resembling a natural membrane. a) liposomes b) micelles c) microsomes d) lysosomes e) a and b 16. Which of the following techniques would most likely be used to separate a protein based on its size? a) thin layer chromatography b) affinity chromatography c) ion-exchange chromatography d) gel filtration chromatography e) more than one of the above 17. The fluidity of the cell membrane decreases a) as the chain length of saturated fatty acids increases. b) as the temperature increases. c) as the amount of unsaturated fatty acids decreases. d) as the amount of cholesterol in the membrane decreases at higher temperatures. e) more than one of the above. 18. Which of the following statements regarding the basement membrane is incorrect? a) The basement membrane provides a barrier to macromolecules moving towards the plasma membrane. b) The basement membrane provides mechanical support for attached cells. c) The basement membrane is a lipid bilayer located at the basal surface of epithelial cells. d) The basement membrane is a sheet that surrounds connective tissue. e) The basement membrane plays a role in cell-cell and cell-surface interactions. 19. Which of the following statements regarding plasmodesmata is incorrect? a) They are lined with plasma membrane. b) The desmotubule provides continuity of cytosol between adjacent cells. c) Proteinaceous particles embedded in the plasma membrane serve as molecular sieves. d) They allow communication between adjacent cells. e) They allow virus particles to move from cell to cell.

6 20. The tendency of a charged ion to diffuse between two compartments within a cell depends upon a) a chemical or concentration gradient b) an electric potential gradient c) the availability of ATP d) an osmotic gradient e) a and b 21. The electron microscope is such a useful tool in cell biology because it provides a) the ability to view unfixed, living samples. b) high magnification. c) high resolution. d) high selectivity. e) high contrast. f) all of the above. 22. Which of the following techniques could be used to identify the transmembrane domain(s) of an integral membrane protein? a) light microscopy b) fluorescence recovery after photobleaching c) thin layer chromatography d) hydropathy plots e) more than one of the above 23. Which of the following statements regarding laminins is correct? a) They are dimeric proteins linked by disulfide bridges b) They consist of a core protein attached to glycosaminoglycans c) They contain a series of globular domains connected by short, flexible segments d) They consist of three polypeptides attached by disulfide bridges e) More than one of the above 24. Which component of an animal cell s ECM plays a similar role to pectin in the plant cell wall? a) collagen b) elastin c) proteoglycans d) fibronectins e) hemicellulose

7 25. What cell structures is osmium tetroxide primarily responsible for fixing and staining so that they can be seen using transmission electron microscopy? a) centrioles b) chromatin c) cell membranes d) microfilaments e) cell walls

8 Section B Provide the correct answer to the questions below. Record your answers in the provided spaces. DO NOT USE ACRONYMS. Section B is worth a total of 20 marks. 1. Name two components of the extracellular matrix involved in primordial cell migration. [2 marks] 2. What does amphipathic mean? [1 mark] 3. Name one adhesive component of plant cell walls. [1 mark] 4. Which structure found in eukaryotic cells is proposed to have evolved from an aerobic heterotrophic prokaryote engulfed by an anaerobic, heterotrophic prokaryote? [1 mark] 5. What is the name of the model proposed to explain the molecular mechanism responsible for ciliary or flagellar motility? [1 marks] 6. Name two actin-binding proteins needed for maintaining microfilaments in highly-ordered bundles in a microvillus. [2 marks] 7. Which technique would most likely be used to separate organelles such as peroxisomes and lysosomes? [1 mark] 8. What is the major protein in the gap junction? [1 mark] 9. What is the term for when an organism can compensate for temperature changes by altering the lipid composition of its membranes? [1 mark]

9 10. What are the two major components of a centrosome? [2 marks] 11. What is the external carbohydrate coating of most animal cells called? [1 mark] 12. This 16 carbon fatty acid can be attached to an internal cysteine residue of certain membrane proteins. [1 mark] 13. What is the term for the simultaneous assembly at one end and disassembly from the other end of a microtubule? [1 mark] 14. What is the name of the jellyfish protein that scientists routinely employ today to study almost all aspects of cell biology? [1 mark] 15. Name two components of lipid rafts. [2 marks] 16. What is the name of the structure shown in the figure on the right? [1 mark]

10 Section C Please record your answers to the questions below in the spaces provided. You are welcome to use well-labeled diagrams and/or bulleted phrases to provide answers to the questions. DO NOT USE ACRONYMS. Section C is worth a total of 20 marks. 1. [8 marks] i) [3 marks] Intact red blood cells were purified and either: 1. left untreated referred to as the 'control' sample 2. treated with trypsin - a protease that digests completely portions of proteins if the sites of digestion are accessible 3. permeabilized with the detergent triton X-100 and then treated with trypsin The plasma membrane fractions from the control sample and the two treatment samples were then recovered by ultracentrifugation and their respective membrane proteins separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS- PAGE). Shown below is a schematic illustration of the results of the SDS-PAGE showing the patterns of five bands representing individual proteins obtained from the three samples described above. Of the five proteins indicated, which could be considered to be (answer by inserting the appropriate number): a) a glycophosphatidylinositol (GPI)-anchored protein? b) the plaque protein vinculin? c) integrin? control intact triton X-100-permeabilized membranes trypsin-treated and trypsin-treated membranes membranes top of gel cathode , 5 1, 2, 5 bottom of gel anode

11 ii) Define the Fluid-Mosaic model. [2 marks] iii) Describe three ways in which the lateral movement of integral membrane proteins in the plasma membrane is restricted. [3 marks] 2. Describe the major functional and structural differences between desmosomes and hemidesmosomes. [3 marks]

12 3. [5 marks] i) Draw and label an individual microfilament AND an individual microtubule. [3 marks] ii) Discuss how the drugs taxol and phalloidin affect the cytoskeleton? [2 marks]

13 4. Discuss FOUR of the five related yet distinct roles for membranes in a typical eukaryotic cell. [4 marks]

14 Section A (Total of 25 marks) Midterm Answer Key 1. c 6. d 11. c 16. d 21. c 2. d 7. b 12. a 17. e 22. d 3. e 8. a 13. b 18. c 23. d 4. a 9. e 14. d 19. b 24. c 5. b 10. e 15. a 20. e 25. c Section B (Total of 20 marks) 1. Name two components of the extracellular matrix involved in primordial cell migration. [2 marks] fibronectins and laminins 2. What does amphipathic mean? [1 mark] Contains both hydrophobic and hydrophilic regions. 3. Name one adhesive component of plant cell walls. [1 mark] lignin or hemicellulose or extensin 4. Which structure found in eukaryotic cells is proposed to have evolved from an aerobic heterotrophic prokaryote engulfed by an anaerobic, heterotrophic prokaryote? [1 mark] mitochondria 5. What is the name of the model proposed to explain the molecular mechanism responsible for ciliary or flagellar motility? [1 marks] sliding-microtubule mechanism 6. Name two actin-binding proteins needed for maintaining microfilaments in highly-ordered bundles in a microvillus. [2 marks] fimbrin, villin 7. Which technique would most likely be used to separate organelles such as peroxisomes and lysosomes? [1 mark] density gradient centrifugation

15 8. What is the major protein in the gap junction? [1 mark] connexin 9. What is the term for when an organism can compensate for temperature changes by altering the lipid composition of its membranes? [1 mark] homeoviscous adaptation 10. What are the two major components of a centrosome? [2 marks] centriole and pericentriolar material 11. What is the external carbohydrate coating of most animal cells called? [1 mark] glycocalyx 12. This 16 carbon fatty acid can be attached to an internal cysteine residue of certain membrane proteins. [1 mark] palmitic acid 13. What is the term for the simultaneous assembly at one end and disassembly from the other end of a microtubule? [1 mark] treadmilling 14. What is the name of the jellyfish protein that scientists routinely employ today to study almost all aspects of cell biology? [1 mark] green fluorescent protein 15. Name two components of lipid rafts. [2 marks] Sphingolipid, cholesterol, lipid anchored proteins 16. What is the name of the structure shown in the figure on the right? [1 mark] axoneme

16 Section C (Total of 20 marks) 1. [8 marks] i) [3 marks] Intact red blood cells were purified and either: 2. left untreated referred to as the 'control' sample 2. treated with trypsin - a protease that digests completely portions of proteins if the sites of digestion are accessible 3. permeabilized with the detergent triton X-100 and then treated with trypsin The plasma membrane fractions from the control sample and the two treatment samples were then recovered by ultracentrifugation and their respective membrane proteins separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS- PAGE). Shown below is a schematic illustration of the results of the SDS-PAGE showing the patterns of five bands representing individual proteins obtained from the three samples described above. Of the five proteins indicated, which could be considered to be (answer by inserting the appropriate number): a) 4 a glycophosphatidylinositol (GPI)-anchored protein? b) 3 the plaque protein vinculin? c) 1 integrin? control intact triton X-100-permeabilized membranes trypsin-treated and trypsin-treated membranes membranes top of gel cathode , 5 1, 2, 5 bottom of gel anode

17 ii) Define the Fluid-Mosaic model. [2 marks] Membranes consist of a mosaic of proteins in a fluid lipid bilayer. iii) Describe three ways in which the lateral movement of integral membrane proteins in the plasma membrane is restricted. [3 marks] Any three of the following -interactions with other membrane proteins -fenced in by the cytoskeleton -anchored to (immobilized by) the cytoskeleton -attached to, and movement directed by the cytoskeleton -restricted by the components of the extracellular matrix 2. Describe the major functional and structural differences between desmosomes and hemidesmosomes. [3 marks] -desmosomes are involved in cell-cell interactions -hemidesmosomes are involved in cell-ecm interactions -the integral membrane proteins found in desmosomes are cadherins -the integral membrane proteins found in hemidesmosomes are integrins -the plaque proteins found in desmosomes are desmoplakin and plakoglobin -the plaque protein found in hemidesmosomes is plectin 3. [5 marks] i) Draw and label an individual microfilament AND an individual microtubule. [3 marks] Labels for a microfilament could include: -correctly label the negative and positive ends -label the f-actin protein -indicate that the microfilament is a helical dimer -8 nm diameter -binds ATP/ADP Labels for a microtubule could include: -correctly label the negative and positive ends -label the α-tubulin and β-tubulin dimer -indicate that the microtubule consists of 13 protofilaments -label the GTP cap -binds GTP/GDP -25 nm diameter

18 ii) Discuss how the drugs taxol and phalloidin affect the cytoskeleton? [2 marks] -taxol binds to and stabilizes microtubules (prevents depolymerization) -phalloidin binds to and stabilizes the microfilaments (prevents depolymerization) 4. Discuss FOUR of the five related yet distinct roles for membranes in a typical eukaryotic cell. [4 marks] Defines the boundaries of the cell and delineates its compartments. Membranes act as selectively permeable barriers to ensure that the interior of the cell or an organelle is physically separated (compartmentalized) from its surrounding environment. Sites of specific function. Membranes carry out specific functions because of the types of proteins (and lipids) embedded/associated within them. Membranes regulate the transport of solutes. Membranes provide for and regulate the transport of substances in and out of the cell and organelles including nutrients, water, etc. The mode of transport across different membranes varies including passive transport (simple and facilitated diffusion), active transport (ATPase pumps), endo- and exocytosis and protein translocation complexes. Recognition and transduction of signals for the surroundings. Membranes serve as the sites were the cell (organelles) receives information in the form of signals (e.g. chemical or electrical) from their surroundings. Most incoming signals are ligands (e.g. hormone molecules) that are recognized by membrane-bound receptors that detect and bind to the ligand and then through the process known as signal transduction initiate a series of events within the cell that lead to a response. Membranes mediate cell-to-cell communication. Membranes contain distinct structures (e.g. gap junctions, plasmodesmata, etc.) that allow for the exchange of substances between neighboring cells and thus provide the means for communication in multi-cellular organisms.