Principles of Cell Biology Exam Notes

Exam Overview

Course: Principles of Cell Biology
Exam Date: November 6, 2012
Total Questions: 75, only one correct answer for each question.

Abbreviations

RER: Rough Endoplasmic Reticulum
SER: Smooth Endoplasmic Reticulum
SRP: Signal Recognition Particle
NO: Nitric Oxide
TGN: Trans Golgi Network
GPCR: G protein Coupled Receptor
RTK: Receptor Tyrosine Kinase
EGF: Epidermal Growth Factor
PDE: Phosphodiesterase
LDL: Low Density Lipoprotein
UPR: Unfolded Protein Response

Exam Questions

1-10

Langmuir and Danielli/Davson are best known for their work on:
- a. Cell membranes
- b. TGN
- c. GPCRs
- d. RTKs
- e. None of the above
Dolichol phosphate plays a key role in:
- a. Proteolytic processing
- b. Formation of multimers from monomers in the RER
- c. Initial protein glycosylation
- d. Targeting mitochondrial proteins to the mitochondria
- e. Adding the address tag to proteins directed to the lysosomes
An integral cell membrane protein that can transport one molecule against its gradient while coupled to transporting another molecule in the opposite direction with its gradient would be considered:
- a. Translocon
- b. Uniporter
- c. Biporter
- d. Antiporter
- e. Symporter
Get 1, 2, and 3 play critical roles in:
- a. Peroxisomal protein targeting
- b. Insertion of tail-anchored proteins
- c. Insertion of GPI-anchored proteins
- d. Nuclear translocation
- e. Chloroplast translocation
A ribonucleoprotein that can be found either soluble or bound to the RER is described as:
- a. Signal peptide
- b. Signal peptidase
- c. Translocon
- d. Hsc 70
- e. SRP

11-20

What key tool was used to show that there are SRP receptors on the RER?
- a. cDNA microarrays
- b. Genomic cloning
- c. Protease inhibitors
- d. Liposomes
- e. None of the above were used to demonstrate this fact
There are a number of drugs useful for investigating the cAMP system. One such drug is forskolin. What is its function?
- a. Directly activates adenylate (adenylyl) cyclase
- b. Blocks the hydrolysis of GTP to GDP
- c. Dimerizes the GPCR
- d. It is a non-hydrolyzable analog of GTP so turns on the G protein in a constitutive manner
- e. Blocks the action of cAMP phosphodiesterase
The freeze-fracture technique was critical to our current fluid-mosaic model of the cell membrane. What was the major contribution in this regard?
- a. It showed that some integral membrane proteins could diffuse within the plane of the membrane while others could not.
- b. It showed that fluorochromes could be used to discern the structure of the cell membrane
- c. It showed that ultrastructural immunocytochemistry could be used to discern the structure of the cell membrane
- d. It revealed a protein-phospholipid-phospholipid-protein sandwich confirming the J.D. Robertson model
- e. None of the above
The signal sequence for RER co-translational translocation:
- a. is at the amino end of the protein
- b. consists of an average of about 25 amino acids that can range from approximately 16-30 in number
- c. is clipped off if the protein is to be secreted
- d. is a substrate for the signal peptidase
- e. All of the above
MDCK cells were chosen to study the location of the influenza HA protein and the VSV G glycoprotein because:
- a. They are polarized with an apical and basal domain
- b. They lack a TGN
- c. They only have post-translational translocation protein synthesis
- d. They are a cell strain that eventually commits apoptosis
- e. All of the above
Generator cell and target cell are terms often used when describing what type of second messenger system?
- a. cAMP
- b. cGMP
- c. IP3/DAG Protein Kinase C system
- d. Calcium/calmodulin
- e. NO
Milstein was one of the first to use a cell-free system to investigate the:
- a. Function of RTKs
- b. Presence of a signal sequence/signal peptidase
- c. The large variety of GPCRs
- d. Protein Kinase B second messenger system
- e. Powerful allure of the Dave Matthews Band
The cell junction that can be investigated with either lanthanum hydroxide applied to the basal side or sodium fluorescein added to the apical side of an MDCK monolayer is:
- a. Tight junction
- b. Gap junction
- c. Adherens
- d. Neurotransmitter synapse
- e. Desmosome
Which of the following would best match the description of being barrel shaped, trimeric transmembrane proteins found in gram-negative bacteria and in the outer membranes of mitochondria and chloroplasts?
- a. Glycophorin
- b. Spectrin
- c. Bacteriorhodopsin
- d. Porins
- e. Ras
Where would you not typically find the Mannose-6-phosphate receptor?
- a. Outer cell membrane
- b. Trans-Golgi network
- c. Vesicles in the constitutive secretion pathway
- d. Late endosome
- e. Clathrin-coated vesicles budding off of the TGN

21-30

Dynamin catalyzed GTP hydrolysis is not well understood but appears to be associated with:
- a. Pinching off of clathrin/AP-coated vesicles.
- b. The tagging of lysosomal proteins so that they traffic properly to the lysosomes
- c. The activation of Ras in RTK
- d. The signal transduction of insulin
- e. The insertion of Type IV proteins into the RER membrane
The transmembrane helix that confers the Gi vs Gs specificity to the GPCR is helix #5. What type of experiment or tool was critical to deduce this information?
- a. Antibodies
- b. Southern blots
- c. Northern blots
- d. Chimeric proteins
- e. Use of cholera toxin
Which of the following describes the regulated secretory pathway?
- a. Small electron lucent vesicles
- b. Fusion of vesicles with an outer membrane not regulated by an influx of calcium
- c. Typical of how collagen is secreted
- d. Not immediately sensitive to protein synthesis inhibitors
- e. None of the above because all are characteristic of the constitutive, not regulated, pathway
Simon and Blobel’s experiment discussed in class that used the novel application of Ohm’s Law was important in the early recognition of:
- a. The lectins involved in protein folding
- b. Molecular chaperones
- c. Chaperonins
- d. The cascade of enzymes that control the UPR
- e. None of the above
What is the molecular basis of familial hypercholesterolemia?
- a. Defective transport of LDL receptors to the outer plasma membrane
- b. Depressed synthesis of LDL receptors and improper folding of these receptors
- c. Problems with the NPXY sorting signal that binds to the AP2 complex
- d. Defective clustering into coated pits
- e. Any one or all can be the basis of familial hypercholesterolemia
Flippase, also known as ABCB4, plays a key role in:
- a. The ability of desmosomes to function
- b. Flipping phospholipids from one leaflet to the other
- c. Protein trafficking between the RER and Golgi
- d. Inverting Type I integral membrane proteins once they are in place in the cell membrane
- e. None of the above
Phototransduction is the ability to translate the interaction of a photon into a change in trans-membrane potential. Which of the following is false concerning this process?
- a. Light causes an inhibition of cGMP phosphodiesterase
- b. Light stimulus decreases cGMP concentration in the outer segment of the photoreceptor
- c. It is a GPCR mediated event
- d. Light stimulus causes the transmembrane potential to hyperpolarize (move farther away from 0 mv)
- e. Low cytosolic cGMP results in closing of the cGMP-gated ion channels
Red blood cells were commonly used to investigate the cell membrane. Which of the following is not one of the virtues of this system that made it a good choice for experimental analysis?
- a. Easy to obtain
- b. Have no nuclei
- c. Demonstrates a unique form of protein trafficking in the RER
- d. Can make inside-out and right-side-out ghosts
- e. Few proteins in the outer plasma membrane compared to most other cells
Which of the following ligands typically targets a cytoplasmic receptor?
- a. NGF
- b. Steroid
- c. LDL
- d. EGF
- e. DMB
One truly amazing cellular event is the ability of a photoreceptor such as the rod to adapt to a large range of light intensities. Which two enzymes below are involved in this process?
- a. Protein Kinase A and Protein Kinase C
- b. Arrestin and rhodopsin kinase
- c. GEF and GAP
- d. Ras and Ran
- e. None of the above

31-40

The type of cell junction that is critical to the tensile (mechanical) strength properties of human skin and which is associated with an internal keratin (intermediate filament) cytoskeleton is:
- a. Tight junction
- b. Gap junction
- c. Adherens
- d. Neurotransmitter synapse
- e. Desmosome
Con A is a lectin and was useful in demonstrating that approximately half of integral membrane proteins are fluid within the plane of the membrane whereas others are less fluid/stationary. To what type of group does a lectin bind?
- a. Phosphate heads of phospholipids
- b. Disulfide groups
- c. Carbohydrate groups
- d. GPI anchors
- e. Not yet known
The effects of Viagra, Cialis and Levitra are mediated by which second messenger system?
- a. NO
- b. cAMP
- c. cGMP
- d. IP3/DAG Protein Kinase C
- e. Calcium/calmodulin
From what organelle is calcium released during the activation of the IP3/DAG Protein Kinase C system?
- a. Mitochondria
- b. Peroxisomes
- c. Endoplasmic reticulum
- d. Proteasomes
- e. Lysosomes
Pemphigus is a disease that affects desmosomes. It is best described as:
- a. Cancer of the skin
- b. Inability to pump glucose across cell membranes
- c. Autoimmune disease against occludin
- d. Failure of red blood cells to have the proper shape that results in crusty skin sores
- e. None of the above adequately describes the clinical basis of Pemphigus
Protein Kinase A:
- a. Contains two regulatory units
- b. Contains two catalytic units
- c. Binds cAMP
- d. Is a tetramer
- e. All of the above
Robert J. Lefkowitz, MD, was honored with the Nobel Prize last month. This alum of Bronx High School did some pioneering work on:
- a. GPCRs
- b. Tight junctions
- c. Protein trafficking in the RER
- d. Protein trafficking from the Golgi to the TGN
- e. Lysosomal address tags
A cell junction that typically encircles cells, uses E-cadherin as the major adhesive molecule, and is associated with F-actin is referred to as:
- a. Tight junction
- b. Gap junction
- c. Adherens
- d. Neurotransmitter synapse
- e. Desmosome
Of the following organelles involved in the receptor-mediated endocytosis system, which has the most acidic pH?
- a. Extracellular environment
- b. Coated pit
- c. Coated vesicle
- d. Cytoplasm
- e. Late endosome
STIM proteins and the store-operated channels play a key role in which second messenger system?
- a. cAMP
- b. cGMP
- c. Calcium/calmodulin
- d. NO
- e. IP3/DAG Protein Kinase C

41-50

Glycogen metabolism is controlled by which second messenger system?
- a. cAMP
- b. cGMP
- c. Protein Kinase C
- d. Calcium/calmodulin
- e. NO
Ras is not:
- a. Associated with RTK signal transduction
- b. A trimeric G protein
- c. A protein that if mutated or defective can cause cancer
- d. In an active form when it binds GTP
- e. A key signal transduction intermediate in the EGF receptor pathway
The NO system is critical in regulating blood pressure. The NO system and its activation involve a number of components. Which of the following is not involved in this cascade?
- a. Protein Kinase G
- b. NO synthase
- c. Calcium/calmodulin
- d. Acetylcholine GPCR
- e. None of the above because all are involved in this cascade
The KDEL peptide is found as a part of what type of protein?
- a. Type I
- b. Type II
- c. Type III
- d. Type IV
- e. RER resident proteins
Cholesterol is a key component of the cell membrane. It is a member of which molecular family?
- a. Sphingolipids
- b. Sterols
- c. Phosphoglycerides
- d. GPI anchor proteins
- e. None of the above
From the beginning to the end of the process, which of the following takes the longest amount of time to complete?
- a. Activation of acetylcholine nicotinic receptor
- b. Activation of acetylcholine muscarinic receptor
- c. Receptor-mediated endocytosis
- d. Activation of a GPCR
- e. Activation of a RTK
Cells use calcium for several second messenger systems. It is important that the cell regulates its free intracellular calcium levels in the cytoplasm – a process called calcium homeostasis. If not regulated, what can happen to the cells if the regulation of calcium is lost?
- a. Cells become transformed from normal cells to cancer cells
- b. Cells die
- c. Cells differentiate
- d. Cells aggregate together due to the presence of calcium-dependent cell adhesion molecules
- e. None of the above
Which type of protein is characterized by a stop-transfer anchor sequence?
- a. Secreted protein – regulated
- b. Secreted protein – constitutive
- c. Type I protein
- d. Type II protein
- e. None of the above
Ligand binding to which type of receptor results in the near immediate influx of sodium and efflux of potassium?
- a. LDL receptor
- b. Transferrin receptor
- c. EGF RTK receptor
- d. Acetylcholine muscarinic receptor
- e. None of the above
Apolipoprotein B (apo B):
- a. Is the ligand for LDL receptor mediated endocytosis that wraps around the LDL particle
- b. Can cause phosphatidylserine to "flip-flop" in the cell membrane
- c. Is what causes the TGN to accumulate proteins when cells are cooled to 20°C.
- d. Is present in the lysosomes and is what hydrolyzes cholesterol to its component parts
- e. None of the above

51-60

Which of the following does not match smooth endoplasmic reticulum?
- a. Can contain high concentrations of calcium such as the sarcoplasmic reticulum that is derived from the SER
- b. Fuses with the TGN during lysosomal protein trafficking
- c. Is tubular in nature
- d. Is physically connected to the RER and can serve as a partial cytoskeleton in special cases
- e. Is the site of synthesis of steroids, fatty acids and phospholipids
The COPII and COP I vesicles mediate protein trafficking between:
- a. The polyribosomes to the RER
- b. The RER to the cis-Golgi
- c. The cis-Golgi to the medial Golgi
- d. The medial Golgi to the trans Golgi
- e. The trans Golgi to the TGN
Many cancer cells can secrete growth factors that, in turn, stimulate their own receptors. What type of extracellular signaling would this fit best?
- a. Plasma-membrane attached proteins
- b. Paracrine
- c. Endocrine
- d. Autocrine
- e. Neurochemical
Salubrinal is a drug that is used to study:
- a. The UPR
- b. Vesicle release from the Golgi to the TGN
- c. Glycosylation of protein in the medial-Golgi
- d. The ability of the SRP to bind to the signal sequence
- e. None of the above
Post-translational translocation is not the common method of RER protein synthesis. BiP plays a key role in this process as described below:
- a. BiP is a G protein that transfers phosphate to the nascent protein
- b. BiP is an integral RER protein like the translocon through which the protein passes
- c. BiP keeps the protein from backsliding through the translocon
- d. BiP facilitates the dissociation of ribosomes into their constituent subunits
- e. None of the above
Which of the following is transported by the transferrin receptor mediated endocytosis system?
- a. Iron
- b. Sodium
- c. Potassium
- d. LDL
- e. Calcium
Which type of receptor exists as separate single membrane spanning monomers but dimerizes and autophosphorylates in response to ligand binding?
- a. GPCRs
- b. Wnt
- c. Hedgehog
- d. RTKs
- e. Notch/Delta
Which of the following is false concerning mAKAPs?
- a. Anchors cAMP phosphodiesterase to the nuclear membrane
- b. Anchors the cAMP regulatory units to the nuclear membrane
- c. Binds the cAMP catalytic unit and travels with it to the nucleus
- d. Is critical for the localized effect of cAMP dependent protein kinase A
- e. None of the above because all are true statements
Experiments were discussed in class on how the issue of autophosphorylation and insulin transduction was studied that ultimately showed that autophosphorylation of the insulin receptor was required for insulin signal transduction. If you were to do these or similar experiments, which of the following probes would be the best choice of those listed?
- a. 3H-thymidine
- b. 3H-leucine
- c. 3H-glucose
- d. 3H-mannose
- e. 35S-methionine
You have a monoclonal antibody for CREB (cyclic AMP responsive element binding protein) and accomplish fluorescence immunocytochemistry. Where might you find your fluorescent probe to be located in cells stimulated with a GPCR ligand that results in cAMP production?
- a. Outer cell membrane
- b. Lysosomes
- c. Late endosome
- d. Soluble within the cytoplasm
- e. Nucleus

61-75

Calreticulin and calnexin:
- a. Are both soluble (not membrane-bound) proteins
- b. Are found exclusively in the mitochondrial matrix
- c. Bind to disulfide groups
- d. Facilitate folding of proteins in the RER
- e. Are ribonucleoproteins
An interesting experiment was discussed that showed in the absence of methotrexate DHFR (dihydrofolate reductase) translocated properly to the mitochondria but when methotrexate was added, the protein was unable to translocate. This focused on:
- a. Cleavage of the signal sequence
- b. Addition of mannose residues to the nascent protein
- c. The importance of maintaining proteins in an unfolded array during post-translational translocation
- d. The ability of select drugs like methotrexate to open up channels for protein translocation
- e. All of the above
Hsc70:
- a. Can be found in the cytoplasm
- b. Can be found in the mitochondrial matrix
- c. Is a molecular chaperone
- d. Is critical to proper mitochondrial protein translocation
- e. All of the above
Which of the following does not occur in the RER?
- a. Address tagging of proteins destined for the lysosomes
- b. Initial glycosylation of proteins
- c. Formation of disulfide bonds
- d. Protein folding and multimeric assembly
- e. Proteolytic cleavage
Fully synthesized proteins found soluble in the cytoplasm can translocate into which of the following organelles?
- a. Peroxisomes
- b. Mitochondria
- c. Chloroplasts
- d. Nucleus
- e. All of the above
8-azido-cAM32P was discussed in class. This probe was useful to study:
- a. COPII vesicles
- b. The PKA regulatory units
- c. The KDEL sequence
- d. V-SNARES
- e. Ras
If you are researching the SNARE complex, what aspect of protein trafficking are you most probably studying?
- a. Formation of the secretory vesicle from the condensing vesicle
- b. Binding of the nascent protein to the RER
- c. Ability of the signal peptidase to recognize the signal sequence
- d. Vesicle targeting
- e. Lysosomal enzyme function
What is the final consequence of proteins that are detected in response to the UPR?
- a. They are covalently linked to ubiquitin and degraded in the proteasome
- b. They are ejected from the cell through receptor-mediated endocytosis
- c. They are endocytosed by lysosomes
- d. They bind to ribosomes
- e. Not yet known
Tom 20, Tom 22 and Tom 40 play key roles in the translocation of proteins to the:
- a. RER
- b. Mitochondria
- c. Chloroplasts
- d. Peroxisomes
- e. Nuclei
If a protein in the cytoplasm has a stromal-import and/or a thylakoid-targeting sequence, this protein is most likely targeting:
- a. RER
- b. Chloroplast
- c. Mitochondria
- d. Lysosome
- e. Peroxisome
Ran-GDP, Ran-GTP and Exportin 1 all play key roles in translocation to which organelle?
- a. Mitochondria
- b. Peroxisome
- c. Lysosome
- d. Nucleus
- e. None of the above
The nature of the TGN was elusive for quite some time until what parameter was manipulated?
- a. Cell temperature
- b. pH of the TGN
- c. pH of the lysosomes
- d. Amount of available oxygen to the cell
- e. Adjacent contact with surrounding cells
GlcNAc (N-acetylglucosamine) phosphotransferase is a critical enzyme found in the cis-Golgi that confers the address tag to lysosomal proteins. What is the abbreviation of this address tag?
- a. DMB
- b. FFD
- c. M6P
- d. STP
- e. SRP
If you were tracking a secreted protein following a typical synthesis path, which compartment would be the last in the series below?
- a. Condensing vesicle
- b. Transitional vesicles
- c. TGN
- d. Cis Golgi
- e. Medial Golgi
You are using brefeldin A and colchicine in your studies. What type of work best matches your research?
- a. Studying the dimerization of GPCRs
- b. Determining the molecular targets of NO
- c. Studying anterograde and retrograde vesicle transport between the RER and the cis-Golgi
- d. Studying how desmosomes can be compromised leading to psoriasis
- e. Analyzing the lateral fluidity of plasma membrane proteins