EXAM 2 CELL BIO
Glycerol is the backbone of the sphingomyelin. T OR F
FALSE PHOSPOLIPIDS TROG;YCERIDES
Most proteins destined to enter the endoplasmic reticulum. Select one: a. are transported across the membrane after their synthesis is complete. b. are synthesized on free ribosomes in the cytosol. c. begin to cross the membrane while still being synthesized. d. remain within the endoplasmic reticulum.
c. begin to cross the membrane WHILE still being synthesized. have an N-terminal signal
You get a cell line with no name, but it says that this cell line forms coated pits but vesicle budding and the removal of coat proteins don't happen. Which of the following proteins might be lacking in this cell line? Select one: a. clathrin b. Rab c. dynamin d. adaptin
c. dynamin
Which of the following choices reflects the appropriate order through which a protein destined for the plasma membrane travels? Select one: a. lysosome → endosome → plasma membrane b. ER → lysosome → plasma membrane c. Golgi → lysosome → plasma membrane d. ER → Golgi → plasma membrane
d. ER → Golgi → plasma membrane
You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given that info, which of the following statements is TRUE? a. Fuzzy has a C-terminal signal sequence that binds to SRP. (b) Only one ribosome can be bound to the mRNA encoding Fuzzy c. fuzzy must contain a hydrophobic stop sequence d. Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be degraded in the ER membrane.
d. Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be degraded in the ER membrane.
the stimulation of auditory nerves depends on the opening and closing of channels in their auditory hair cells. Which type of gating mechanism do these cells use ? a. volatge-gated b. extracellular ligand- gated c. intracellular ligand- gated d. stress-gated
d. stress gated
After isolating the rough endoplasmic reticulum from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you expect the RNA from the rough endoplasmic reticulum to encode? A. soluble cytoplasmic proteins a. plasma membrane proteins b. ER membrane proteins B. nuclear proteins C. peripheral membrane proteins bound to the cytoplasmic c. soluble secreted proteins d. proteins with the signal peptide (d) none of the above
none OR d. proteins with the signal peptide b. ER membrane proteins a. plasma membrane proteins c. soluble secreted proteins
Transporters, in contrast to channels, work by... specific or non-specific binding?
transporters= specific but slower binding channels = less speciifc
*Scramblase catalyzes* transfer of random phospholipids from one leaflet to another to on____. (a) ER (b) Lysosome (c) Peroxisome (d) Golgi.
(a) ER
Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks? (a) Flippase (b) phospholipases c) convertases (d) glycosylases
(a) Flippase
Which of the followings affect the mobility of a protein in *SDS-PAGE*? (a) Number of total amino acids (b) Number of amino acids with charged side chain (c) Percentage of hydrophobic amino acids (d) Number of Glycine
(a) Number of total amino acids
Imagine that you have engineered a set of gene encoding a protein with signals for import into mitochondria and ER retention signal (KDEL only). Which compartment will be the destination of the protein? (a) mitochondria (b) cytoplasm (c) ER lumen (d) lysosome
(a) mitochondria
The endothelial cells found closest to the site of an infection express proteins called ???. Each ??? binds to a particular _______ that is presented on the surface of a target cell.
(a) oligosaccharide LECTIN
______ activates GTPase activity of Ras. (a) GEF (b) GAP (c) channel (d) tyrosine kinase
(b) GAP gap activates an inhibitory RX, this rx INHIBITS RAS does not activate proteins
If K+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected? (a) The membrane potential is not affected by K+. (b) It becomes more negative. (c) It becomes more positive. (d) It is permanently reset.
(b) It becomes more negative.
Which of the following best describes the behavior of a *gated channel*? (a) It stays open continuously when stimulated. (b) It opens more frequently in response to a given stimulus. (c)It opens more widely as the stimulus becomes stronger. (d)It remains closed if unstimulated.
(b) It opens more frequently in response to a *given stimulus*
Ca 2+ -pumps in the plasma membrane and endoplasmic reticulum are important for _____________. (a) maintaining osmotic balance. (b) preventing Ca 2+ from altering the activity of molecules in the cytosol. (c) providing enzymes in the endoplasmic reticulum with Ca 2+ ions that are necessary for their catalytic activity. (d) maintaining a negative membrane potential (e) maintaining the cytosolic concentration of Ca 2+ low.
(b) preventing Ca 2+ from altering the activity of molecules in the cytosol. & (e) maintaining cytosolic concentration of Ca 2+ low.
Which of the following statements is true? (a) The signal sequences on mitochondrial proteins are usually at the C-terminus. (b) Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria. (c) Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes. (d) Mitochondrial proteins cross the membrane in their native, folded state
(c) *Chaperone proteins in the mitochondria facilitate* the movement of proteins across the outer and inner mitochondrial membranes. (a) FALSE= The signal sequences on mitochondrial proteins are usually at the C-terminus. TRUTH:*N-Terminus* (b) False- Most mitochondrial proteins are NOT *imported* from the *cytosol* but are *synthesized* inside the *mitochondria* TRUTH: *they ARE* (d) FALSE- Mitochondrial proteins cross the membrane in their native, folded state TRUTH: *unfolded*
Which one of the following is not one of the three major types of coated vesicles? (a) COPI (b) COPII (c) COPIII (d) Clathrin
(c) COPIII
We can test the relative permeability of a phospholipid bilayer by using a synthetic membrane that does not contain any protein components. Some uncharged, polar molecules are found to diffuse freely across these membranes, to varying degrees. Which of the following has the lowest rate of diffusion across an artificial membrane? (a) glycerol (b) Nitric Oxide (c) H+ (d) ethanol (a) sucrose (b) hydrogen peroxide
(c) H+ (a) sucrose /glucose
Accumulation of misfolded proteins in the ER lumen triggers an Unfolded Protein Response (UPR) that involves ____ of Chaperone proteins. (a) Ubiquitylation (b) Acetylation (c) Transcription (d) Methylation
(c) Transcription
The Ras protein is a GTPase that functions in many growth-factor signaling pathways. In its active form, with GTP bound, it transmits a downstream signal that leads to cell proliferation; in its inactive form, with GDP bound, the signal is not transmitted. Mutations in the gene for Ras are found in many cancers. Of the choices below, which alteration of Ras activity is most likely to contribute to the uncontrolled growth of cancer cells? (a) A mutation that *increases the affinity* of Ras for GDP (b) A mutation that *decreases the affinity* of Ras for GTP (c) A mutation that *decreases the affinity of Ras for its downstream* targets. (d) A mutation that *decreases the rate of hydrolysis* of GTP by Ras.
(d) A mutation that *decreases the rate of hydrolysis* of GTP by Ras.
A recent study showed that optogenetical activation of neural circuits in Hypothalamus induced aggressive behavior of the mouse. Which ion is the first target of regulation by the optogenetics of this study? (a) Ca2+ (b) H+ (c) K+ (d) Na+
(d) Na+
The small GTPase _____ regulates tethering of the v-SNARE containing vesicles to its target membrane. (a) Dynamin (b) Ran (c) Ras (d) Rab
(d) Rab Rab proteins are involved in the recognition of the transport vesicle with its target membrane and not with vesicle budding
______ is the sorting station of *outward* secretory pathway. (d) trans-Golgi (b) cis-Golgi (c) Endosome (d) ER
(d) trans-Golgi receiving = CIS
Which of the following is required for the *secretion of neurotransmitters in response to an action potential*? (a). neurotransmitter receptors (b). Na+-K+ pumps (c). voltage-gated K+ channels (d). voltage- gated Ca2+ channels
(d). voltage- gated Ca2+ channels
Bacterial porin proteins form large, barrel-like channels in the membrane. Which of the following is NOT TRUE about these channels? -They are made primarily of β-sheets/ α-helices. - They can/cannot form narrow channels. - They have/do not have alternating *hydrophobic & hydrophilic AA*
-They are made primarily of β-helices. - They cannot form narrow channels. - They have alternating *hydrophobic & hydrophilic AA*
active transport required the input of energy into a system so as to move solutes against their electrochemical and conentration gradients. Which of the following is one common way to perform active transport ? A. Na+-coupled B. Cl-coupled C. SO^2/4- coupled d. PO^3/4-coupled
A. NA coupled
This membrane vesicle will undergo fusion with the plasma membrane. After the event of fusion, which membrane leaflet will face cytoplasmic side? A. solid line B. broken line
A. SOLIDE LINE = cytoplasmic/ c-terminus *note* broken line = N-temrinus (ER)
WHAT WOULD HAPPEN IF/..... A. You add a signal sequence (for the ER) to the N-terminal end of a normally cytosolic protein. B. You change the hydrophobic amino acids in an ER signal sequence into charged amino acids. C. You change the hydrophobic amino acids in an ER signal sequence into other hydrophobic amino acids. D. You move the N-terminal ER signal sequence to the C-terminal end of the protein. 1. The protein will now be transported into the ER lumen. 2. The protein will still be delivered into the ER. It is the distribution of hydrophobic amino acids that is important, not the actual sequence. 3. The protein will *NOT enter the ER*. Because the C-terminus of the protein is the LAST part to be made, the ribosomes synthesizing this protein will not be recognized by the signal-recognition particle (SRP) and hence not carried to the ER 4. The altered signal sequence will not be recognized and the protein will remain in the cytosol.
A. w/ 1. The protein will *NOW enter the ER* B. w/ 4. not recall & stay in cytosol C. w/ 2. still into ER D. w/ 3. The protein will *NOT enter the ER*
Which of the following membrane lipids does not contain a fatty acid tail?
CHOLESTEROL nor SDS
________ inhibits Dopamine transporter and thus increases dopamine concentration at the synapse
COCAINE
Which of the following statements about vesicle budding from the Golgi is FALSE? a. Clathrin molecules are important for binding to and selecting cargos for transport. b. Adaptins interact with clathrin. c. Once vesicle budding occurs, clathrin molecules are RELEASED from the vesicle. d. Clathrin molecules act at the cytosolic surface of the Golgi membrane and plasma
Clathrin molecules are important for binding to and *selecting cargos for transport*. selecting = dynamin *note* they are involved in the *initial shaping of the vesicle* into the pit
Whihc of the following protein is a GTP binding protein ? A. V-Snare B. T-SNARE C. Adaptin D. Rab
D. Rab
The resting membrane potential of ANIMAL cells varies but almost always is a *negative value* or 60mv T OR F
FAKSE -resting membrane = 0 mV bc the + & - are in balance -normanlly positive b/c Na+ = @ resting memebrane no ion enetrs or exit
A *sodium potassium antiport* of an epithelial cell transports luminal glucose to the epithelial cells T OR F
FALSE
A neurotransmitter released at the synapses always activates its target T or F
FALSE
Phophatases hydrolyze GTP and thus INACTIVATES small GTP binding protein. (a)True (b)False
FALSE
Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them OFF. T OR F
FALSE
Pinocytosis is the major way of HIV infection to immune cells. T OR F
FALSE
The voltage sensitive *Sodium* channel has a specific Km value T or F
FALSE
a symport would function as an antiport if orientation in the membrane was reversed T OR F
FALSE
Transmembrane proteins cross the the plasma membrane as an unfold polypetide T or F
FALSE folded
Pinocytosis is carried out by F-Actin driven process that are independent of clathrin-coated pits and vesicles. T OR F
FALSE uses clathrin
A passive *glucose uniport* is localized to the apical membrane of an epithelial tissue. T OR F
FALSE BASOLATERAL side (inhibits the transport of glucose back to the lumen, its a directional movement: cytosol to the ExtraCMatrix)
An electrical signal is converted into a chemical signal at the synapse by a stress gated chloride channel T OR F
FALSE LIGAND-GATED
A *sodium glucose antiport* of an epithelial cell transports glucose to the connect tissue. T OR F
FALSE SYMPORTER *located on the APICAL side* (faces the gut)
Gap junction/tight junctions permits highly selective ion transport T OR F
FALSE TRANSPORTER PROTEINS
A protein can be embedded on the cytosolic side of the membrane bilayer by employing a hydrophobic α helix. T OR F
FALSE An embedded protein employs an amphipathic helix
Membrane proteins that pump ions in and out of the cell are classified as enzymes T or F
FALSE are in the functional class of *transporters*
*Lipid-linked* proteins are classified as peripheral membrane/transmembrane proteins proteins because the polypeptide chain does not pass through the bilayer. T OR F
FALSE integral membrane proteins
The *lateral motility* of membrane proteins can be restricted by GAP junctions T OR F
FALSE gap junction helps *TIGHT JUNCTION* inhibits
Which of the following statements about the endoplasmic reticulum (ER) is false? (a) The rough ER is the major site for new membrane phospholipid synths in the cell (b) Proteins to be delivered to the ER lumen are synthesized on smooth ER. (c) Steroid hormones are synthesized on the smooth ER. (d) The ER membrane is contiguous with the Golgi Complex (e) The proteins in the lumen of the ER will be easily reduced.
FLASE: -The ROUGH ER is the major site for new membrane *phospholipid* synths in the cell TRUE: The *SMOOTH* ER is the major site for new membrane synthesis in the cell. FALSE: *Proteins* to be delivered to the ER lumen are synthesized on SMOOTH ER. TRUTH: lumen are synthesized on *ROUGH ER* (c) Steroid hormones are synthesized on the smooth ER. (TRUE) FALSE: The ER membrane is contiguous with the GOLGI Complex TRUTH: contiguous w/ *outer NUCLEAR membrane* FALSE: (e) The proteins in the lumen of the ER will be easily REDUCED. TRUTH: *OXIDIZED*
Transmembrane proteins cross the plasma membrane as an *unfolded OR folded* polypeptide
FOLDED folded in alpha helix in nucleus too!
Calcium channel is open during hyperpolairzation T OR F
False DEPOLARIZATION
GTP= GDP=
GTP= bound & *active*, leads to cell proliferation GDP= bound & *INACTIVE*, signal not transmitted
The .....of the integral membrane proteins on the ER is often *glycosylated*
LUMINAL side
Proteins destined to go to the *extracellular space* interact with : N-terminal OR C-terminal
N-term
Proteins destined to go the *lysosomal lumen* can interact with: (a) N-terminus (b) C-terminus
N-terminus
Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport? Select one: a. Nuclear transport receptors would be unable to bind cargo. b. Nuclear transport receptors would be unable to enter the nucleus. c. Nuclear transport receptors would be unable to release their cargo in the nucleus. d. Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils.
Nuclear transport receptors would be unable to release their cargo in the nucleus.
*INNER* leaflet of the plasma membrane is enriched with _____
PS - PKC (*phosphatidylSERINE*) PI - PH domain proteins (*PhosphatidyLINOSITOL*) PE- (*phosphatidylETHANOLAMINE*)
......... is the most abundant phospholipid found in cell membranes.
Phosphatidylcholine
......channel is open during *hyper polarization* step
Potassium K
This membrane vesicle will undergo fusion with a lysosome. *After the event of fusion*, which membrane leaflet will face cytoplasmic side? (a) solid line (b) broken line
SOLID LINE
_____ is more enriched at the *outer leaflet* of the plasma membrane
SPHINGOMYELIN
Membrane lipids......
THEY DO: -*DIFFUSE* within membrane -lateral movement -rotation - flexing of hydrocarbon chains DO NOT : Flip-floP *switch btw lipid layers*
A GTP-binding protein exchanges its bound GDP for GTP to become ACTIVATED. T OR F
TRUE
A protein that relies on Protein-Protein interactions to stabilize its membrane association is classified as a *peripheral membrane protein* because it can be dissociated without the use of detergents. T OR F
TRUE
CHOLESTEROL equally locates tot he outer and inner leaflets of the plasma membrane T OR F
TRUE
The extracellular side of the integral membrane protein is often glycosylated T OR F
TRUE
A voltage-gated *K+* channel adopts two alternative conformations T OR F
TRUE Na+ = 3
A voltage-gated Na+ channel adopt three alternative confimations T OR F
TRUE K+ = 2
Which of the following statements is true? (a) Phospholipids will spontaneously form liposomes in nonpolar solvents. (b) In eukaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer. (c) Membrane lipids diffuse within the plane of the membrane. (d) Membrane lipids frequently flip-flop between one monolayer and the other
TRUE= C- Membrane lipids diffuse within the plane of the membrane. FALSE: a. Phospholipids will spontaneously form liposomes in *POLAR* solvents. B. Nuclei and mitochondria are enclosed by *2 MEMBRANES* D. Membrane lipids = *NO FLIP-FLOP*
What is the role of the nuclear localization sequence in a nuclear protein? a. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. b. It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. c. It aids in protein unfolding so that the protein can thread through nuclear pores. d. It prevents the protein from diffusing out of the nucleus through nuclear pores.
a. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. -contains *positively charged* AA, not hydrophobic ones -Proteins are FOLDED as they enter -Proteins are ACTIVELY TRANSPORTED not diffuse through the nuclear pores
flow of action potential -*Depolarization* = getting less negative -*Voltage-gated Ca+ channels* -*Action potential* propogated -Negative to *positive* membrane b/c Na+ channels opens & goes in -*hyperpolarization* (when action potential reaches it peak) K+ channels open,
action potential occurs when the cell becomes *depolarization* -triggered by a value that is *less negative* than the resting membrane potential. -The action potential is propagated by the opening of *voltage-gated Ca+ channels* - During an action potential, the membrane potential changes from *negative to positive* - The action potential travels along the neuron's axon -> nerve terminals-> branched dendrites. -*outflow* of K helps to bring cell back to membrane resting potential normally k in Na out
This membrane vesicle will undergo fusion with a lysosome. After the event of fusion, proteins in the *cytoplasmic side* can interact with: (a) N-terminus (b) C-terminus
b) C-terminus
The figure below shows the organization of a protein that normally resides in the plasma membrane. The boxes labeled 1 and 2 represent membrane-spanning sequences and the arrow represents a site of action of signal peptidase. Given this diagram, which of the following statements must be true? a. The N-terminus of this protein is cytoplasmic. b. The C-terminus of this protein is cytoplasmic. c. The mature version of this protein will span the membrane twice, with both the N and C-termini in the cytoplasm. d. None of the above.
b. The C-terminus of this protein is cytoplasmic.
Which of the following choices reflects the appropriate order through which a protein destined for the plasma membrane travels to a lysosome a. plasma membrane - golgi- lysosome b. plasma membrane- endosome - lysosome (c) Golgi - plasma membrane lysosome d. ER - plasma membrane- lysosome
b. plasma membrane- endosome - lysosome
You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given that info, which of the following statements is FALSE? A. Fuzzy has a N-terminal signal sequence that binds to SRP. b. Multiple ribosome can be bound to the mRNA encoding FUZZY during translation c. Fuzzy does not contain a hydrophobic stop-transfer seq. d. even after the signal seq from fuzzy has been cleaved, the signal will still associate wit fuzzy in the ER.
d. even after the signal seq from fuzzy has been cleaved, the signal will still associate wit fuzzy in the ER. -n-termnal - multiple riobosomes - no hydrophobic stop
proteins in the CYTOSOL do or do not contain sorting signals
do NOT contain a sorting signal
if k channels are opened in a cell that was previously at rest, how will the membrane potential be affected
it becomes hyperpolarized
GTP-binding proteins typically have GTPase activity, and the hydrolysis of GTP transforms them to the "off" conformation. t or f
true
a protein that relies on protein-protein interactions to stabilize its membrane association is classified as *peripheral membrane* protein because it CAN be dissociated *without* the use of *Triton X-100/detergents*
true