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Flashcards in Test 2 Practice Deck (48):

T or F: CLATHRIN is the primary coat protein utilized for endocytosis.



T or F: SNARE PROTEINS are responsible for vesicle function.



T or F: CALMODULIN is the major calcium sensor in most cell types and it binds four calcium ions



T or F: Pleckstrin homology domains (PH-domains) are signaling domains that recognize PHOSPHORYLATED TYROSINE.

False, PIP3


T or F: Synaptic transmission relies on SHORT-LIVED signals while endocrine signals are LONG-LIVED signals.



T or F: Heterotrimer G-proteins are ALWAYS activated by a seven-span receptor.



T or F: Peroxisomes, like MITOCHONDRIA, can import fully folded proteins or protein complexes.

False, nucleus


T or F: SYNAPTOTAGMIN is a calcium binding protein involved in neurosecretion.



T or F: PROSTAGLANDINS are arachidonic acid metabolites while dopamine is an amino acid derivative.



T or F: MG2+ is the primary second messenger generated by activated of phospholipase C-beta.

False, Ca2+


T or F: The signal for O-LINKED sugar addition is the amino acid sequence N-X-S/T.

False, N-linked


T or F: The major function of the MEDIAL Golgi is protein sorting.

False, Trans


T or F: POTASSIUM ions concentrations are kept very low in the cytoplasm.

False, calcium


T or F: The NUCLEOPLASM is topologically the same as the cytoplasm.



T or F: Nucleocytoplasmic transport is UNIDIRECTIONAL.

False, bidirectional


T or F: Signaling molecules that bind to intracellular receptors must be HYDROPHILIC.

False, hydrophobic


T or F: Signal patches are most appropriate for proteins that are transported while UNFOLDED.

False, folded


T or F: The OXA PROTEIN TRANSLOCATOR is critical for translocating mitochondrial genome-encoded proteins across the inner mitochondrial membrane.



T or F: RAB PROTEINS serve as communicators between the vesicle tethering machinery and the SNAREs.



T or F: Mechanistic parallels exist between viral fusion proteins that allow virus entry and SNARE proteins that fuse transport vesicles.



T or F: Complex oligosaccharides and high mannose oligosaccharide CANNOT be attached to the same protein.

False, can


Name the two main translocation complexes in the mitochondrial outer membrane and describe their primary function.

TOM complex: required for import of all nuclear encoded genes and helps insert membrane proteins into outer membrane. SAM complex: helps insert and fold beta-barrel proteins


What are the major roles of ESCRT-0, ESCRT-1, ESCRT-2, and ESCRT-3 in formation of multivesicular bodies?

ESCRT-0: binding and sequestering cargo on the surface of a cell. ESCRT-1,2: accumulates in neck of MVB to promote budding. ESCRT-3: cleave the buds to form vesicles


Why is the steroid hormone receptor the most direct signal transduction system?

Hormones are lipid soluble and their receptors are intracellular, so they can easily pass through membrane. Therefore, unlike other receptors, second messengers are not necessary. In addition, these hormones are ligand activated, so changes in gene expression are easier.


What are the three sorting decisions of proteins in the trans Golgi network?

Secretory: proteins in a vesicle wait near the PM until signaled to fuse with membrane and release contents; Exocytotic: proteins in vesicles travel directly to PM and immediately release contents; Lysosomal: filled with digestive enzymes that are destined to become part of lysosome


Name and describe the two mobile electron carriers involved in electron transport.

Ubiquinone: carry either one or two electrons and shuttles electrons between complex I and complex III. Cytochrome c: soluble protein that shuttles an electron at a time from complex III to complex IV.


Receptor-activated G-proteins interact with a variety of downstream effectors such as adenylyl cyclase and phospholipase C-beta. What second messenger molecule(s) is/are generated by activation of phospholipase C-beta?

Phospholipase C-beta cleaves (PI(4.5)P2) into diacylglycerol and IP3. IP3 serves as a ligand for the ER calcium channel to open up.


You are trying to express a mouse ER luminal enzyme in E. coli in order to conduct in vitro functional assays. (You have an expression construct encoding the final processed protein – i.e., without a signal sequence, which the bacteria would not be able to remove.) You are able to obtain large amounts of protein of the expected length and sequence, but the protein is not active. Why might this be? How can you get around this problem?

Don't know


Describe the two ways in which a single membrane-spanning protein can be inserted into the ER in a Type 1 orientation (COOH-in cytosol).

Don't know


Name three ER chaperones and describe their function.

BiP: binds to unfolded proteins and prevents aggregation; Calnexin and Calreticulin: calciu-binding proteins that bind to oligosaccharides on incompletely folded proteins and prevents aggregation; PDI: enzyme that aids in folding by helping correct disulfide bond formation


Are nuclear localization sequences removed from proteins once they are used? Why or why not?

No, because during mitosis, the contents of the nucleus must leave. If the signals were removed, then the nuclear proteins would not be able to return to the nucleus once mitosis is completed.


When a mitochondrial uncoupling agent such as FCCP or DNP is added to a flask of respiring tissue culture cells, oxygen consumption continues but no ATP is made. Why?

Uncoupling agents allow H+ to traverse the membrane without first passing through ATP synthase. This process does not allow ATP synthesis because instead of traveling through ATP synthase, the H+ would travel directly through the membrane.


You are examining the cellular response to a new drug. You treat cells with the drug and measure the intracellular level of cAMP and find that cAMP is increased in response to the treatment. With what type of receptor would you predict the drug interacts?

G-protein receptor


Describe a signal transduction pathway that would result in an increase in

Activation of a G-protein receptor which increases adenylyl cyclase. Adenylyl cyclase converts ATP to cAMP, so an increase would result in more cAMP.


How is the rise in intracellular cAMP used to change cellular physiology or

cAMP activates Protein Kinase A (PKA), which phosphorylates many downstream proteins. For example, in muscles, PKA leads to glycogen breakdown, an acute response. In addition, cAMP activates CREB, which results in a delayed response.


Inclusion-cell (I-cell) disease is an autosomal recessive disorder of lysosomal storage and results from a defective GlcNAc phosphotransferase. Typical symptoms of I-cell disease are failure to thrive and developmental delays. What’s the normal function of GlcNAc phosphotransferase?

Enzyme in the cis Golgi that binds to lysosomal proteins and UDP-GlcNAc and catalyzes the transfer of GlcNAc phosphate to a terminal mannose residue.


With a deficiency of GlcNAc phosphotransferase, where would these
lysosomal proteins go? Will they still be active?

Lysosomal proteins would either stay in the Golgi and remain inactive or be secreted from the cell by vesicles.


Coxiella burnetii is an obligate intracellular bacteria. In order to survive, the bacteria must invade living eukaryotic cells by taking advantage of the secretory pathway. During infection, the bacteria must allow itself to be internalized by eukaryotic
cells using a specialized form of endocytosis. Name this process.

Phagocytosis, which allows for import of full bacteria.


Coxiella burnetii can only divide in an environment close to 5.0 pH. Name the
organelle that best fits this description, and explain the mechanism used by the cell to create the low pH environment within the organelle.

Lysosomes, which achieve this through constant import of H+ up its gradient through H+ pumps.


You are tracking the route of a newly synthesized oligomeric plasma membrane receptor from the ER to the plasma membrane. What type of coat is used for export from the ER?

COPII coat is used for export from the ER.


Describe the mechanism of vesicle generation from the ER.

COPII budding is initiated by membrane budding of GTP-binding SAR1. Then, Sec23/24 begin to build a coat around Sar1 and the cargo. Sec13/31 finishes the coat. These proteins all contribute to a bud, which then becomes a vesicle.


What additional protein(s) must this vesicle contain to ensure the correct targeting and fusion of this vesicle?

First, the vesicle must contain Rab proteins on its surface so that it can associate with the PM tether. In addition, the vesicle must contain v-SNAREs so that it may associate with t-SNARES at the membrane.


Once the coat forms the vesicle, the coat becomes an impediment. How is this type of coat removed?

SAR1 cleaves its GTP to GDP and turns it back into the off state. Once SAR1 is removed, the rest of the coat removes.


How could you modify the primary sequence of the protein if you want to selectively retain this membrane protein in the ER?

Insert a KKXX motif in the cytoplasmically exposed tail. This will be recognized by COPI and return it to the ER.


What type of coat would be used for the return trip to the ER?

COPI coat.


A fluorescent organic dye (gray) was microinjected into the cytoplasm of the cells shown in Panel A-C. Describe, in roughly quantitative terms, the relative size of the dyes used in A-C.

A: less than 1000 daltons - can freely diffuse into through NPC. B: Between 1000 and 5000 daltons that can diffuse through NPC but at a slower rate than A. C: Larger than 5000 daltons, but limited by size of NPC itself.


A quantum dot with a peptide containing the sequence PPKKKRKV coupled to the surface was injected in Panel D. Describe, in detail, the process of selective accumulation of this molecule in the nucleus.

Nuclear import receptors bind to the quantum dot at the sequence and are able to be imported into the nucleus. There, the complex associates with Ran-GTP to release the cargo.


Describe one way to shift the localization of the Qdot used in part b from the localization in Panel D to that seen in panel C.

Use an inhibitor to block the specific nuclear import receptor of the Qdot, so that it will not bind.