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.
Marks
Section B
Section C
1.
2.
3.
4.
Total for B and C
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)
b)
c)
d)
e)
2.
Robert Brown
Matthias Schleiden
Rudolf Virchow
Theodor Schwann
Louis Pasteur
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)
b)
c)
d)
e)
4.
passive diffusion.
a facilitative transporter.
a voltage-gated channel.
a ligand-gated channel.
direct active transport.
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.
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)
b)
c)
d)
e)
6.
Which of the following characteristics is shared by prokaryotes and eukaryotes?
a)
b)
c)
d)
e)
7.
density
size
charge
shape
more than one of the above
Which of the following compounds could be composed of fatty acyl chains, a glycerol
backbone, a phosphate group and inositol.
a)
b)
c)
d)
e)
9.
The presence of a nucleus
The presence of mitochondria
Extensive RNA processing
The presence of ribosomes
None of the above
In sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), individual
proteins migrate in the electric field at rates determined by their
a)
b)
c)
d)
e)
8.
F-actin
S1 myosin fragment
talin
α-actinin
more than one of the above
phospholipid
sphingolipid
glycophosphatidylinositol (GPI)-anchored protein
sterol
glycolipid
Which class of integral membrane proteins join cells of similar type to one another?
a)
b)
c)
d)
e)
laminins
vinculins
integrins
collagens
cadherins
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)
b)
c)
d)
e)
microfilaments.
intermediate filaments.
hemicellulose.
spectrin.
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)
b)
c)
d)
e)
brightfield microscopy
phase contrast microscopy
confocal laser-scanning microscopy
transmission electron microscopy
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)
b)
c)
d)
e)
Gorter and Grendal
Davson and Danielli
Robertson
Singer and Nicholson
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)
b)
c)
d)
e)
gap junctions
tight junctions
desmosomes
focal adhesions
adherens junctions
14. Where would you most likely find cellulose macrofibrils arranged in different layers
oriented at different angles?
a)
b)
c)
d)
e)
cytoplasm
primary cell wall
middle lamella
secondary cell wall
basal membrane
15. These are fluid-filled, membrane-bound spherical vesicles surrounded by a single,
continuous lipid bilayer, resembling a natural membrane.
a)
b)
c)
d)
e)
liposomes
micelles
microsomes
lysosomes
a and b
16. Which of the following techniques would most likely be used to separate a protein based on
its size?
a)
b)
c)
d)
e)
thin layer chromatography
affinity chromatography
ion-exchange chromatography
gel filtration chromatography
more than one of the above
17. The fluidity of the cell membrane decreases
a)
b)
c)
d)
e)
as the chain length of saturated fatty acids increases.
as the temperature increases.
as the amount of unsaturated fatty acids decreases.
as the amount of cholesterol in the membrane decreases at higher temperatures.
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)
b)
c)
d)
e)
They are lined with plasma membrane.
The desmotubule provides continuity of cytosol between adjacent cells.
Proteinaceous particles embedded in the plasma membrane serve as molecular sieves.
They allow communication between adjacent cells.
They allow virus particles to move from cell to cell.
20. The tendency of a charged ion to diffuse between two compartments within a cell depends
upon
a)
b)
c)
d)
e)
a chemical or concentration gradient
an electric potential gradient
the availability of ATP
an osmotic gradient
a and b
21. The electron microscope is such a useful tool in cell biology because it provides
a)
b)
c)
d)
e)
f)
the ability to view unfixed, living samples.
high magnification.
high resolution.
high selectivity.
high contrast.
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)
b)
c)
d)
e)
light microscopy
fluorescence recovery after photobleaching
thin layer chromatography
hydropathy plots
more than one of the above
23. Which of the following statements regarding laminins is correct?
a)
b)
c)
d)
e)
They are dimeric proteins linked by disulfide bridges
They consist of a core protein attached to glycosaminoglycans
They contain a series of globular domains connected by short, flexible segments
They consist of three polypeptides attached by disulfide bridges
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)
b)
c)
d)
e)
collagen
elastin
proteoglycans
fibronectins
hemicellulose
25. What cell structures is osmium tetroxide primarily responsible for fixing and staining so that
they can be seen using transmission electron microscopy?
a)
b)
c)
d)
e)
centrioles
chromatin
cell membranes
microfilaments
cell walls
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]
________________________________________________________________________
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]
________________________________________________
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 (SDSPAGE). 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
membranes
top of gel
cathode
intact
trypsin-treated
membranes
triton X-100-permeabilized
and trypsin-treated
membranes
1
2
3
3
4
1
5
bottom of gel
anode
2, 5
1, 2, 5
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]
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]
4. Discuss FOUR of the five related yet distinct roles for membranes in a typical eukaryotic
cell. [4 marks]
Midterm Answer Key
Section A (Total of 25 marks)
1.
2.
3.
4.
5.
c
d
e
a
b
6.
7.
8.
9.
10.
d
b
a
e
e
11. c
12. a
13. b
14. d
15. a
16.
17.
18.
19.
20.
d
e
c
b
e
21.
22.
23.
24.
25.
c
d
d
c
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
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
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 (SDSPAGE). 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
membranes
top of gel
cathode
intact
trypsin-treated
membranes
triton X-100-permeabilized
and trypsin-treated
membranes
1
2
3
3
4
1
5
bottom of gel
anode
2, 5
1, 2, 5
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
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.