Cell Bio Exam 3

False

Securin is degraded when the spindle assembly checkpoint is active

True

Executioner caspases can exist as active or inactive dimers

True

Receptor tyrosine kinases commonly possess cytosolic kinase domains

False

Parkin ubiquitinates mitochondrial proteins to mark dysfunctional mitochondria for pexophagy

True

S-CDK triggers centrosome duplication during interphase of the cell cycle

20S subunit

Proteosome subunit containing proteolytic sites

Helicase

Enzyme that unwinds a DNA double helix during replication

H. Robert Horvitz

Nobel prize recipient for studies on programmed cell death

Lysosome

Organelle at which autophagy occurs

CDC25 phosphatase

Phosphatase that removes an inhibitory phosphate on CDK

Actinomycin

Cytoskeletal filament in the eukaryotic cytokinetic ring

Telophase

Stage of mitosis when the nuclear envelope reassembles

Intrinsic/mitochondrial

Apoptosis pathway that is regulated by cytochrome C

Late G1 checkpoint

Checkpoint after which a cell commits to cell cycle entry

Autophagy

Autophagic destruction of protein aggregates

ATF6

ER protein that possesses latent transcription factor activity

Frameshift mutation

Mutation that results in a deletion of a nucleotide pair

Astral MTs

Microtubules whose plus ends interact with the cell cortex

Microautophagy

Type of autophagy that does not involve an autophagosome

Apaf1

Adaptor protein within an apoptosome

E. None of the above

Which of the following mutations would inhibit apoptosis?

A. A mutation in an IAP protein that prevents its association with initiator caspases

B. A mutation in an IAP protein that prevents its association with executioner caspases

C. A mutation in Bcl2 that prevents it from inhibiting Bak oligomerization

D. A mutation in iCAD that prevents it from inhibiting CAD endonuclease

E. None of the above

C. short cells

Which of the following phenotypes would you expect to observe in S. pombe when Wee1 kinase is inhibited?

A. T-shaped cells

B. long cells

C. short cells

D. cells that undergo multiple rounds of cytokinesis at once

E. normal size cells

B. Replication origins are generally GC rich

Which of the following statements about DNA replication is false?

A. DNA primase catalyzes an RNA primer for DNA synthesis

B. Replication origins are generally GC rich

C. A sliding clamp allows the DNA polymerase to be highly processive

D. Both the leading and lagging strands are synthesized in the 5’ → 3’ direction

E. DNA replication occurs through a semiconservative mechanism

E. None of the above

Which of the following statements regarding cell signaling is true?

A. In endocrine signaling, signals are released from a cell and bind to receptors on its own cell surface

B. Synaptic signaling is a type of endocrine signaling

C. Endocrine signaling relies on local mediators

D. Endocrine signaling commonly involves neighboring cells that communicate through direct physical contact

E. None of the above

E. Both A and C

Which of the following motor proteins help(s) to move the two centromeres away from each other?

A. dynein

B. kinesin-14

C. kinesin-5

D. both A and B

E. both A and C

C. promote the association of Upf proteins with an improperly spliced mRNA molecule

Exon-junction complexes…

A. recognize and mark boundaries between exons and introns

B. are added to an mRNA molecule in the cytosol

C. promote the association of Upf proteins with an improperly spliced mRNA molecule

E. none of the above

D. A and B

Which of the following is/are associated with activation of the spindle assembly checkpoint?

A. Mad2 localization to kinetochores

B. Inhibition of separase

C. Cohesin degradation

D. Both A and B

E. all of the above

C. possesses unfoldase activity that unfolds folded polypeptides

The 19S subunit of the proteasome:

A. has multiple proteolytic sites

B. forms a cap that recognizes multiubiquitinated proteins

C. possesses unfoldase activity that unfolds folded polypeptides

D. both A and C

E. both B and C

E. all of the above

Initiator and executioner caspases are similar in which of the following ways?

A. They both act in the intrinsic pathway of apoptosis

B. They both exist as dimers in their active form

C. They both cleave proteins at aspartate residues

D. both A and B

E. all of the above

C. death receptor

Which of the following proteins acts most upstream in the extrinsic pathway of apoptosis:

A. initiator caspase

B. executioner caspase

C. death receptor

D. BH-3-only proteins

E. cytochrome C

B. is invariant among different individuals

Cell death during C. elegans development…

A. occurs predominantly in hypodermal cells

B. is invariant among different individuals

C. destroys >50% of the cells that are originally made

D. is not visible by DIC microscopy

E. is always lethal to the organism

C. one leading strand and one lagging strand

Each DNA parent strand within a DNA replication bubble acts as a template strand that produces:

A. either one leading strand or one lagging strand

B. either two leading strands or two lagging strands

C. one leading strand and one lagging strand

D. multiple leading and lagging strands

E. a primer strand whose base-pair sequence is identical to the template strand

D. BH3-only proteins

Which of the following proteins acts most upstream in the intrinsic pathway of apoptosis?

A. initiator caspase

B. MAPKKK

C. death receptor

D. BH3-only proteins

E. cytochrome C

B. prevent dissociation of the G_alpha subunit from the G_beta and G_gamma subunits

A mutation that blocks the GEF activity of a G-protein coupled receptor would likely:

A. causes GTP to remain constitutively bound to the G_alpha subunit

B. prevent dissociation of the G_alpha subunit from the G_beta and G_gamma subunits

C. interfere with binding between the receptor and its associated trimeric G-protein

D. prevent autophosphorylation of the receptor

E. have no effect on downstream signal transduction

C. gamma phosphate

Radioactively-labeled ATP can be used to mark phosphorylated proteins in live cells. To perform such experiments, which phosphate of ATP must be replaced with ³²P?

A. alpha-phosphate

B. beta-phosphate

C. gamma-phosphate

D. all must be labeled with ³²P

E. none of the above

MAP kinase kinase

Many protein kinases phosphorylate other protein kinases to regulate their activity. Name one protein kinase that is phosphorylated by each of the following protein kinases:

a) MAP kinase kinase kinase?

MAP kinase

Many protein kinases phosphorylate other protein kinases to regulate their activity. Name one protein kinase that is phosphorylated by each of the following protein kinases:

b) MAP kinase kinase?

Cdc²/CDK

Many protein kinases phosphorylate other protein kinases to regulate their activity. Name one protein kinase that is phosphorylated by each of the following protein kinases:

C) Wee1 kinase?

Receptor tyrosine kinase (they phosphorylate each other)

Many protein kinases phosphorylate other protein kinases to regulate their activity. Name one protein kinase that is phosphorylated by each of the following protein kinases:

D) a receptor tyrosine kinase?

An incorrect residue at the site where Wee1 is phosphorylating. Even if Wee1 kinase is functioning correctly, it would still not be able to phosphorylate the CDK and it would not stop the entrance into mitosis. A mutation in these cells, such as a missense mutation, or they might have a faulty mechanism for DNA repair.

You mutagenize S. pombe cells and identify mutants that have a wee phenotype. To your surprise, you find that Wee1 kinase is expressed normally in the mutant cells. If Wee1 kinase is present, what could explain the wee phenotype of these mutants? Describe one possibility.

The signaling mechanism that would trigger a slow response could be the synthesis of a new protein from scratch (DNA→RNA→Protein). A post-translational modification would be much quicker, because the protein would already be present, and all you would have to do is change it (like phosphorylating the protein).

Extracellular signals can trigger fast or slow responses. Describe a signaling mechanism that would trigger a slow response, and one that would trigger a fast response. Explain why.

Misfolded proteins must be retrotranslocated to the ER, because they build up and cause protein aggregates which is detrimental to the cell. A mutation that caused the enzyme mannosidase to become inactive would keep the proteins in the ER, because it could not create an oligosaccharide for lectin to bind to. A mutation of the E3 ubiquitinating ligase, that is attached to the translocation machinery, that makes the enzyme nonfunctional would prevent the protein from being recognized by the protease and would not be degraded. A mutation of lectin, that causes it to not bind to the oligosaccharide, would also affect retrotranslation.

Why must misfolded proteins in the ER be retrotranslocated into the cytosol in order to be degraded? Describe two mutations that would interfere with retrotranslocation of misfolded proteins from the ER to cytosol?

The temperature sensitive mutants were suspended in different stages of the cell cycle, based one the block and release method. Another method was to label the proteins through isotopic labeling of ATP. They also changed different residues where phosphorylation could occur and determined which residue was crucial for the cell cycle. For example, they change the Tyr15 residue to Phe15 and found that the cells entered mitosis too quickly.

How are the temperature-sensitive S. pombe mutants used to study phosphorylation of CDK during the cell cycle? Explain two approaches.

M-cyclin is degraded at the end of mitosis by the APC/C ubiquitin ligase, which becomes active only after proper chromosome alignment - ensuring orderly exit from mitosis.

The regulated ubiquitination of cyclin proteins controls cell cycle progression. When is M-cyclin degrade? What enzyme complex targets M-cyclin for degradation, and why is it able to do so specifically at this point in the cell cycle?

The Fas ligand acts through the extrinsic pathway because of their signaling method. The homotrimeric signal and receptor is indicative of the extrinsic pathway. The overexpression of the secreted protein might make cancer survive because there will be competition between the different binding sites, which makes the binding of the ligand incorrect, thus preventing apoptosis.

Fas ligand forms a homotrimeric signal on killer lymphocytes that stimulates apoptosis in target cells. Do you suppose that Fas ligand acts through the intrinsic or extrinsic pathway of apoptosis, and why? Interestingly, cancer cells have been found to overexpress a secreted protein that binds to Fas ligand. How would you imagine that overexpression of this secreted protein might contribute to the survival of the cancel cells?

True

Parkin-mediated ubiquitination marks dysfunctional mitochondria for mitophagy

False

During the cell cycle, most cell growth occurs during M phase

False

Nonhomologous end joining repairs a DNA strand to its original sequence19

19S cap

Proteasome subunit that unfolds incoming polypeptides

Lectin

General name for a sugar-binding protein

Lysosome

Acidic organelle that can digest protein aggregates

Pexophagy

Autophagic destruction of peroxisomes

S phase

Cell cycle phase in which most histone synthesis occurs

B. both kinetochores of a sister chromatid pair are attached to microtubules from the same centrosome

Syntelic microtubule-kinetochore attachments are ones in which:

A. high tension is established

B. both kinetochores of a sister chromatid pair are attached to microtubules from the same centrosome

C. both kinetochores of a sister chromatid pair lack microtubule attachments

D. one kinetochore of a sister chromatid pair is attached to microtubules from both centrosomes

E. biorientation has been achieved

A. has multiple active sites

The 20S subunit of the proteasome:

A. has multiple active sites

B. forms a cap that recognizes polyubiquitinated proteins

C. proteolyzes polypeptides only once as they are fed through

D. possesses unfoldase activity that denatures folded polypeptides

E. digests dysfunctional mitochondria

D. both A and B

Which of the following proteins is/are proteolytically cleaved by initiator caspases?

A. initiator caspases

B. executioner caspases

C. iCAD

D. both A and B

E. both A and C

B. It resolves overhangs at chromosome ends

Which of the following is not a characteristic of telomerase?

A. It possesses an RNA molecule that acts as a template

B. It resolves overhangs at chromosome ends

C. It lengthens chromosome ends

D. It works at both ends of a chromosome

E. It recognizes repeated sequences at chromosome ends

C. chaperone-mediated autophagy

In which type of autophagy are single proteins targeted for destruction one-by-one?

A. macroautophagy

B. microautophagy

C. chaperone-mediated autophagy

D. mitophagy

E. none of the above

B. recognition of a particular oligosaccharide motif by lectin

Translocation of misfolded proteins from the ER to the cytosol involves:

A. vesicular transport

B. recognition of a particular oligosaccharide motif by lectin

C. the hydrolysis of GTP as an energy source

D. polyubiquitination within the ER lumen

E. the crossing of two membranes

C. all bound exon junction complexes will be displaced from the mRNA during translation

An mRNA molecule undergoes correct splicing. You would expect that:

A. all introns have not been removed from the mRNA

B. Upf proteins will target the mRNA for rapid degradation

C. all bound exon junction complexes will be displaced from the mRNA during translation

D. the mRNA will not undergo subsequent rounds of translation

E. none of the above

C. death receptor

Which of the following proteins acts most upstream in the extrinsic pathway of apoptosis:

A. initiator caspase

B. executioner caspase

C. death receptor

D. BH3-only proteins

E. cytochrome C

A. leading

A replication fork is shown below. The strand labeled 2 is called the … strand

A. leading

B. lagging

C. template

A. The apoptotic cell releases some of its cytoplasmic contents to induce inflammation

Apoptotic cells are efficiently phagocytosed by neighboring cells of macrophages. Which of the following does not normally happen in this process?

A. The apoptotic cell releases some of its cytoplasmic contents to induce inflammation

B. The apoptotic cell exposes phosphatidylserine at its surface

C. The apoptotic cell rounds up and detaches from its neighbors

D. All of the above normally happen in this process

E. None of the above normally happen in this process

C. Activation of an upstream guanine nucleotide exchange factor

GTP-binding proteins are normally activated by which of the following?

A. GTP hydrolysis by the protein

B. Activation of an upstream GTPase-activating protein

C. Activation of an upstream guanine nucleotide exchange factor

D. Phosphorylation of a bound GDP molecule by an upstream enzyme

E. Release of inorganic phosphate after GTP hydrolysis

In Drosophilia melanogaster, loss-of-function mutations in either Pink1 or Parkin show similar phenotypes including impaired ability to fly, male sterility, and degeneration of dopaminergic neurons. Transgenic