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Examination
5MO021 / 3MB002 Cell Biology, V10
Date:
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February 19, 2010
09.00 - 15.00
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The exam contains two parts, I) multiple choice questions and II) short answer questions.
Each part starts with instructions on how to answer the questions.
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Part I: Multiple Choice questions,
- Circle the correct answer
- Mark only one answer per question
- If you change your answer, be sure that all previous marks are erased completely.
Incomplete
erasures may be read as multiple answers
- Each correctly answered question will be awarded 1p
Q1: The different phospholipids in biological membranes….
A) are present in the same molecular ratios in all membranes of a single organism
B) are present in the same molecular ratios in both halves of the bilayer
C) move rapidly in the plane of the membrane
D) move rapidly from one half of the bilayer to the other
E) are the most important carriers of ions across the membranes
Q2: To alter membrane fluidity, cells can adjust the number of double bonds in their….
A) cholesterol molecules
B) phospholipids
C) integral membrane proteins
D) carbohydrates
E) lipid-bound proteins
Q3: Which of the following molecules has the highest rate of diffusion across a phospholipid
bilayer?
A) ATP
B) serine
E) K+
D) NO
E) insulin
Q4: You are studying the transport of a certain type of molecule into cells. You find that
transport slows down when the cells are poisoned with a chemical that inhibits energy
production. Under normal circumstances, the molecule you are studying is probably
transported into the cell by….
A) simple diffusion.
B) facilitated transport.
C) active transport.
D) osmosis.
E) exocytosis.
Q5: Which phospholipid is negatively charged?
A) Phosphatidylcholine
B) Phosphatidylserine
C) Phosphatidylethanolamine
D) Sphingomyelin
E) All of the above
Q6: Which of the following polymers are not connected through covalent bonds?
A) RNA
B) Peptide
C) Glycogen
D) DNA
E) Microtubules
Q7: While viewing a slide of rapidly moving sperm cells, a student concludes that these cells
require a large amount of energy to maintain their activity. The organelle that most directly
provides this energy is known as….
A) Golgi apparatus
B) Centrosome
C) ribosome
D) mitochondrion
E) lysosome
Q8: During nuclear import which of the following occurs? Pick the TRUE statement
A) The nuclear import receptor uses the energy from the hydrolysis of Ran-GTP to Ran GDP
to bind cargo with a NLS.
B) The nuclear import receptor releases its cargo when Ran-GTP binds to a conserved
loop in the receptor.
C) The nuclear import receptor simultaneously binds Ran-GDP and cargo with a NLS.
D) The nuclear import receptor releases its cargo when Ran-GDP binds to a conserved loop in
the receptor.
E) The nuclear import receptor releases its cargo when Ran GEF promotes the exchange of
Ran-GDP to Ran-GTP.
Q9: Insulin is a protein that is produced by certain pancreatic cells and secreted into the
bloodstream. Which of the following choices best describes the route of insulin from its
production to its exit from the cell?
A) Rough ER, Golgi, plasma membrane
B) Rough ER, transport vesicles, Golgi apparatus, transport vesicles, plasma membrane
C) Rough ER, lysosomes, transport vesicles, plasma membrane membrane
D) Rough ER, Golgi apparatus, smooth ER, cell membrane
E) Rough ER, plasma membrane
Q10: Vesicles are transported from the ER to the Golgi apparatus along….
A) microtubules
B) microtubules and intermediate filaments
C) intermediate filaments
D) actin filaments
E.) actin filaments and intermediate filaments
Q11: What is the known function of SNARE proteins?
A) Forming transport vesicles
B) Controlling the initial trafficking and docking of transport vesicles to target membranes
C) Mediating fusion of transport vesicles with target membranes
D) Ensuring that only properly folded proteins are packaged into transport vesicles
E) Mediating vesicle attachment to actin filaments
Q12: Which of these polymers is abundant inside the nucleus?
A) collagen
B) intermediate filaments
C) actin filaments
D) microtubules
E) All of the above
Q13: It has been proposed that mitochondria are modern descendants of primitive forms of
prokaryotic cells that took up residence within primitive cells and evolved there. Which one
of the following is false evidence for this view?
A) Prokaryotic cells and mitochondria have similar DNA
B) Mitochondria have prokaryotic ribosomes
C) Mitochondria can conduct their own protein synthesis
D) Mitochondria have a complete set of genes, therefore they can function independently
of the host's genes
E) None of the above
Q14: Only certain cells in the body are target cells for the steroid hormone aldosterone.
Which of the following is the best explanation for why these are the only cells that respond to
this hormone?
A) Only target cells are exposed to aldosterone
B) Only target cells contain receptors for aldosterone
C) Aldosterone is unable to enter nontarget cells
D) Nontarget cells destroy aldosterone before it can produce its effect
E) Nontarget cells convert aldosterone to a hormone to which they do respond
Q15: Arrestin helps "reset" signal transduction pathways involving G proteins by….
A) binding to receptors, preventing them from phosphorylating themselves
B) phosphorylating receptors, preventing them from interacting with G proteins
C) binding to phosphorylated receptors, preventing them from interacting with G
proteins
D) binding to phosphorylated G proteins, preventing them from interacting with receptors
E) stimulating G proteins to hydrolyze GTP to GDP
Q16: Which of the following statements most accurately describe the activation of Akt:
A) Akt is phosphorylated by PI 3-kinase, recruited to the membrane and then activate by
PDK1.
B) PI 3-kinase creates docking sites for PDK1 and Akt at the plasma membrane,
facilitating phosphorylation of Akt by PDK1.
C) PI 3-kinase phosphorylates PDK1, which in turn phosphorylates Akt, activating it.
D) A receptor tyrosine kinase acts through Grb to activate Ras which activates MAP kinase
which phosphorylates and activates Akt.
E) PI 3-kinase cleaves PIP2 into diacylglycerol (DAG) and IP3. IP3 activates PDK1 which, in
turn, phosphorylates and activates Akt.
Q17: Suppose you thoroughly and adequately examined a particular type of human cells,
using microscopy, and discovered that it completely lacked actin filaments. You would then
conclude with absolute certainty that this cell also lacked….
A) transcription from the actin gene
B) splicing of the primary transcript from the actin gene
C) translation of actin mRNA
D) both A), B) and C)
E) none of the above
Q18: Most of the ATP consumed during skeletal muscle contraction is hydrolyzed by….
A) Actin
B) Tropomyosin
C) ADF/Cofilin
D) CapZ
E) Myosin II
Q19: Place the following structures in order of size, from the smallest to the largest.
1. Protofilament
2. Microtubule
3. α-tubulin
4. Tubulin heterodimer
5. Mitotic spindle
A) 3,2,4,1,5
B) 5,1,2,4,3
C) 2,3,4,1,5
D) 3,4,1,2,5
E) 3,4,5,1,2
Q20: The stage of mitosis when sister chromatids separate from each other and migrate to
opposite poles of a cell is called…..
A) interphase
B) prophase
C) metaphase
D) anaphase
E) telophase
Q21: Which of the following in NOT correct about p53.
A) p53 functions in growth arrest
B) p53 functions in apoptosis
C) p53 is induced by DNA damage
D) p53 regulates Rb expression
E) p53 regulates p21 expression
Q22: BCL2 is an oncogene and functions in…..
(A) the intrinsic apoptotic pathway to prevent cell death
(B) promoting progression through the G2/M cell cycle checkpoint
(C) preventing DNA repair.
D) promoting mitogen signaling
E) an anti-growth signalling pathway and protects the cell from this type of signaling
Q23: Which of the following is a characteristic function of a tight junction?
A) Forms connection between desmosomes
B) Stabilizes intermediate filaments
C) Allows passage of ions and small molecules between the cytosol of neighbouring cells
D) Prevents flow of fluids between cells
E) None of the above
Q24: Which cell-matrix junction are integrins and keratin intermediate filaments part of?
A) tight junctions
B) hemi-desmosomes
C) desmosomes
D) adherens junctions
E) focal adhesions
Q25: The process of angiogenesis during tumor growth involves….
A) Endothelial cell proliferation
B) Endothelial cell migration
C) Matrix degradation
D) Cell signaling
E) All of the above
Q26: The diameter of most animal cells ranges from….
A) 1.0 to 10 µm.
B) 0.01 to 0.1 µm.
C) 10 to 100 µm.
D) 100 to 1000 µm.
E) 0.1 to 1.0 µm.
Q27: Which of the following is a feature found in BOTH prokaryotic and eukaryotic cells?
A) extensive array of intermediate filaments
B) multiple linear chromosomes in each cell
C) ribosomes that accomplish protein synthesis
D) mitotic spindles that partition chromosomes into the daughter cells
E) All of the above are found in both types of cells.
Q28: Knowing what you know about phospholipid bilayers; if you wanted to build your own
membrane protein, what would your amino acids need to have in order to stay in the
membrane?
A) negatively charged groups
B) hydrophilic groups
C) positively charged groups
D) hydrophobic groups
E) glycosylations
Q29: What make parts of the endoplasmic reticulum rough? The presence of….
A) budding vesicles
B) proteins in the membrane
C) ribosomes
D) glycosylations
E) intermediate filaments
Q30: The proteins that make up the electron transport chain in animals are located….
A) on the outer mitochondria membrane
B) on the inner mitochondria membrane
C) in the mitochondria matrix
D) in the cytoplasm
E) in the nucleus
Q31: CFTR is a human plasma membrane glycoprotein. If a cell is currently synthesizing
CFTR, in what areas of the cell will these proteins be found?
A) Plasma membrane, Golgi apparatus and smooth endoplasmic reticulum
B) Plasma membrane, Golgi apparatus and rough endoplasmic reticulum
C) Plasma membrane, lysosomes and rough endoplasmic reticulum
D) Plasma membrane, vesicles, Golgi apparatus and rough endoplasmic reticulum
E) Plasma membrane
Q32: A researcher made an interesting observation about a protein that was translocated into
the rough endoplasmic reticulum (ER) during its synthesis and eventually ending up in the
plasma membrane. Significantly, the protein in the plasma membrane was found to be slightly
larger than the cognate protein in the ER. The protein was probably changed in the…
A) Golgi apparatus
B) smooth endoplasmic reticulum
C) mitochondrion
D) nucleus
E) lysosome
Q33: Clathrin, a member of the coating protein family, is responsible for….
A) Bending the membrane into a pit
B) Directing the vesicles to the proper compartment
C) Pinching off of the vesicle from the donor compartment
D) Fusing the vesicle to the target compartment
E) The transport of the vesicle along microtubules
Q34: Lysosomes can be expected to be present in large numbers in cells which….
A) secrete peptide hormones
B) are migrating
C) are actively dividing
D) carry out phagocytosis
E) replicate DNA
Q35: If a cell makes both a signaling molecule and the receptor for that signaling molecule,
what is this mode of signaling termed?
A) Paracrine
B) Endocrine
C) Autocrine
D) Neuronal
E) Contact dependent
Q36: Which of the second messengers listed below remains bound to the plasma membrane?
A) Diacylglycerol
B) Ca2+
C) IP3
D) cAMP
E) cGMP
Q37: Which of the signaling receptors are/is generally activated by dimerization induced by
binding to two sites on their ligand?
A) Gated ion channels
B) G protein-coupled receptors
C) Receptor tyrosine kinases
D) Steroid hormone receptors
E) All of the above
Q38: Place the following steps in the correct order in the mammalian Ras signaling pathway:
1. Activation of Ras
2. Activation of a tyrosine kinase transmembrane receptor
3. Activation of MAP kinase
A) 3Æ1Æ2
B) 2Æ3Æ1
C) 2Æ1Æ3
D) 1Æ2Æ3
E) 1Æ3Æ2
Q39: What is the key event that leads to association of a protein with a proteosome?
A) phosphorylation
B) acetylation
C) glycosylation
D) ubiquitination
E) methylation
Q40: Which of the following would INHIBIT the onset of mitosis?
A) binding of M Cyclin to Cdk
B) phosphorylation of Cdk by Wee1
C) phosphorylation of Wee1 by Cdk
D) dephosphorylation of Cdk by Cdc25
E) None of the above
Q41: The stage of mitosis when chromosomes condense to form rod-shaped structures visible
under the microscope is called….
A) interphase
B) prophase
C) metaphase
D) anaphase
E) telophase
Q42: When ATP binds to the head of myosin II it promotes…..
A) binding of myosin to a new actin subunit
B) pivoting of the myosin head and generation of movement
C) release of actin
D) formation of myosin filaments
E) none of the above
Q43: Which of the following processes during animal cell division is not mediated by
microtubules?
A) Movement of the chromosomes to the poles of the cell
B) Movement of the chromosomes to the metaphase plate
C) Contraction of the cleavage furrow
D) Positioning of the cleavage furrow
E) Separation of the centrosomes
Q44: Which of the following modifications occur on nuclear lamins during mitotic entry,
which causes nuclear lamina to disassemble and nuclear envelope to rupture?
A) Glycosylation
B) Ubiquitination
C) Phosphorylation
D) GTP binding
E) Cyclin binding
Q45: A given haploid S. cerevisiae (baker’s yeast) strain has a temperature-sensitive mutation
that inactivates its hexokinase enzyme at the high (restrictive) temperature. (Hexokinase
catalyzes the first reaction in the glycolysis pathway.) A culture of this mutant is grown on
glucose/minimal salts medium (glucose is the only energy source under these conditions) and
then shifted to the restrictive temperature for a couple of hours. Which of the alternatives
below describes the cell cycle stage of most of the cells in the culture?
A) G1 phase
B) S phase
C) G2 phase
D) M phase
E) A mix of cells in G1, S, G2 and M
Q46: Which of the following events is NOT a change experienced by a typical cell committed
to apoptosis?
A) Loss of mitochondrial membrane functions
B) Cytoskeleton collapses
C) DNA breaks into fragments
D) Cell swells and ultimately bursts
E) Nuclear envelope disassembles
Q47: Dye injected into an epithelial cell might be able to enter an adjacent cell through a …..
A) tight junction
B) microtubule
C) desmosome
D) adherence junction
E) gap junction
Q48: Glycosaminoglycan polysaccharides are found on serine and threonine residues in….
A) proteoglycans
B) collagens
C) laminins
D) elastins
E) integrins
Q49: What is acquired during the progression of ALL tumors?
A) loss of the RB gene
B) mutations
C) the ability to synthesize mitogens
D) activation of tumor suppressors
E) loss of the p53 gene
Q50: Which British scientist is credited with coining the term "cell" from the Latin cellulae?
A) Robert Hooke
B) Tord Hagervall
C) Martin Gullberg
D) Anna Arnqvist
E) Ulrich von Pawel-Rammingen
Q51: What would happen in a cell in which the Importins were specifically deficient in Ran
binding?
Answer: Persistent binding between the nuclear import receptor Importin and NLS-containing
proteins in the nucleus. This because Ran-GTP is essential for dissociation of the Importin –
cargo complex. See Albert e al (p 708, Fig. 12-14) and Lecture material Lecture 2, .ppt 29 31
Q52: Consider the synthesis of a multi-pass transmembrane protein. After the protein has
been transferred through Golgi and reached the plasma membrane, which end of the protein
will be on the extra-cellular side? Motivate your answer.
Answer:
A) N-terminal in ER-lumen (translation starts with the N-terminal amino acid (Met).
B) N-terminal since the C-terminus will remain in the cytosol during the passage of the
secretory pathway (
Q53: Explain why the SRP has to temporarily halt translation until the ribosome is positioned
at the pore of the endoplasmic reticulum.
Answer: If the translation would continue, the protein would start to fold in the cytosol, which
for many reasons may prevent translocation into ER by the Protein translocator. Note –
translocation occur co-translational.
(See Albert et al, p733 and Lecture 3 .ppt 10 - 11)
Q54: In a rare human disease lysosomes are lacking most of their ordinary enzymes. Instead
these enzymes are found to be secreted from the cell. Provide a likely molecular mechanism
behind this disorder.
Answer: Inclusion cell disease! Mutations in the gene encoding GlcNAcphosphotransferase (which add the phosphate to mannose). Since the phosphate group on
mannose is critical for recognition by the M6P receptor (and consequent sorting into vesicles
that fuse with lysosomes), the hydrolytic lysosomal enzymes will be secreted. (See Albert e al
(p785-786) and Lecture 3 .ppt 25, note that the M6P receptor mechanism for sorting was not
mentioned during lectures.)
Q55: What is the principle chemical distinction between signaling molecules that bind to cellsurface receptors and those that bind to intracellular receptors?
Answer: Charge, hydrophobicity, size and polarity are important determinants of whether a
molecule may pass through a lipid bilayer or not .
(See Albert et al, p881, Fig. 15-3, Note the need or carrier proteins to keep hydrophobic
ligands soluble in the blood. Lecture 4 &5 .ppt 6, 23, 27 - 29)
Q56: What is calmodulin and what does it do?
Answer: Calmodulin has no enzymatic activity but act by binding and activating other
proteins in its Ca+ bound form. In some cases calmodulin serves as a permanently associated
regulatory subunt of an enzyme complex.
(See Albert et al, p914-16, 1030, Figs. 15-43, 15-44. Lecture 4 &5 .ppt 47, 43)
Q57: How come that a given tyrosine kinase receptor may induce different signals in different
cell types. Hint: SH2 domain proteins determine the output of tyrosine kinase receptor
stimulation.
Answer: Different cell types express different sets of SH2-domain containing signaling and/or
adaptor protein.
(See Albert et al, p924-897, Figs. 15-53, 15-54, 15-55. Lecture 4 &5 .ppt 20, 46)
Q58: Phosphatidylinositol specific kinases phosphorylate the inositol ring of this
phospholipid at specific positions. Which one of these kinases is of key regulatory importance
to generate a PH-domain binding site and how does generation of such binding sites result in
activation of PKB/Akt?
Answer: The phosphoinositide-3 kinase, which phosphorylates the inositol ring on carbon
atom 3
(See Albert et al, p627, p932 – 935, Figs. 15-63, 15-64, Lecture 4 &5 .ppt 50-53)
Q59: You have established a cell line that is deficient for Bak, Bax, and Puma (i.e., this cell
line lacks functional Bak, Bax, and Puma proteins due to mutational inactivation of the
cognate genes). If you micro-inject cytochrome C into the cytosol of cells of this cell line,
what would happen? Motivate your answer.
Answer: Relevant info in Albert et al: p1122 and p1123 (Note that only the anti-apoptotic
Bcl2 proteins, e.g., Bcl2 and Bcl-XL have all 4 BH domains)
A) Bak & Bax are the main BH123 proteins (all BH123 proteins are pro-apoptotic!) in
mammals and at least one of these proteins is required to allow a mammalian cell to activate
the intrinsic apoptotic pathway. Moreover, if apoptosis is induced by irradiation, it implies a
p53 dependent apoptotic pathway, which depends on both Bax and Puma (see .ppt 48). Thus,
there are two reasons why a cell line deficient for Bak, Bax, and Puma would not undergo
apoptosis in response to DNA damage.
B) Release of cytochrome C into the cytosol is the trigger for caspase activation through the
intrinsic apoptotic. Thus, as long as the cells have an intact system for activation of caspases,
injection of cytochrome c into the cytosol will induce apoptosis.
Q60: After the discovery of the non-equilibrium polymerization kinetic of microtubules (i.e.,
dynamic instability), cell biologists were speculating on the role of this energy-demanding
polymerization behaviour. This resulted in the proposal of the “search and capture” model.
Which microtubule-dependent processes does this model explain?
Answer: PH synopsis – ppt 37, 38, Capping of MT at kinetochores during prometaphase,
Capping of the plus end stabilizes specific MTs.
Search and capture provides a mechanism to find specific structures in the cytosol that
depends on “stochastic movements and sensing” rather than “vision or smell”. Note that
different types stabilizing contact points will be sensed during interphase and mitosis (plasma
membrane cues versus kinetochores)
Q61: Rigor mortis refers to the stiffened state of the body of a deceased, which appear a
couple of hours after death and lasts up to 72 hours. Rigor mortis is a consequence of the
ending of aerobic respiration. Provide a molecular explanation to this phenomenon.
Answer: PH synopsis – ppt 42, 45, 46 (role of ATP binding and hydrolysis for myosin
binding, conformational change and release from actin filaments).
1. ATP levels diminish after death, the ER associated (or rather sarcoplasmic reticulum
associated), ATP dependent Ca2+ pump will cease to function Æ leakage of Ca2+ into
the cytosol and consequent muscle contraction by the normal tropomyosin dependent
mechanism (note Ca2+ conc. gradients between cytosol, extracellular fluid and ER/
sarcoplasmic reticulum).
2. Given that myosin binds to actin fibers in the absence of ATP but requires ATP for
detachment/translocation, diminishing ATP will lock up sarcomeres and make all
muscles stiff.
3. During subsequent cellular necrosis, release of proteases from e.g. lysosomes will
cause degradation of all kinds of proteins including the proteins of the sarcomers.
Curiosa: A muscle cell is a syncytiom (hundred of cells are fused Æ hundreds of nucleous)
and may contain 100,000 sarcomeres. The myofibrils of smooth muscle cells are differently
arranged and CaM/caldesmon have the cognate function of tropomyosin).
Q62: It is common that tumors with defects in the pathway defined by the retinoblastoma
tumor suppressor gene product (i.e., the Rb pathway) also have a defective p53 tumor
suppressor gene product. Why is that so?
Answer: Relevant .ppt in Lecture 6 & 7 and Lecture 12
Q63: Which are the essential properties that a normal epithelial cell has to acquire in order to
progress to a malignant carcinoma?
Answer: Relevant .ppt: in Lecture 12