Cell Bio Exam 4

The stages of mitosis were originally defined by cellular features observable through a light microscope. The six micrographs below show animal cells (lung cells from a newt) during the five stages of mitosis, plus cytokinesis. (Note that interphase is not represented in these micrographs.) In these images, the chromosomes have been stained blue, microtubules green, and microfilaments red.

(see picture) As these six micrographs demonstrate, cellular events observable by light microscopy can be used to define the six stages of mitosis and cytokinesis. However, deciphering which stage is which in real cells can be much more challenging than in the drawings of idealized cells you see in your textbook. Thus, it is important to carefully observe the completeness of the mitotic spindle and the location of the chromosomes, as well as how condensed the chromosomes are.

Describe two pieces of evidence supporting the idea that angiogenesis is required for tumors to grow beyond a tiny clump of cells. Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

-Cancer cells injected into an isolated rabbit thyroid gland kept alive with a nutrient solution fail to link up to the organ's blood vessels, the tumors grow to 1-2 mm in diameter. When injected into live animals, the same tumors become infiltrated with blood vessels and grow to enormous size. -Cancer cells placed in the anterior chamber of a rabbit's eye, where there are no blood vessels, remain alive and reach 1-2 mm in diameter. In contrast, cancer cells placed directly on the iris become infiltrated with blood vessels and the tumors grow to enormous size.

Describe the three main stages involved in metastasis, including a description of the relevant cellular properties. Describe the third stage involved in metastasis. Select the two correct statements.

-During the third step, the sites to which cancer cells tend to metastasize are determined by the location of the first capillary bed encountered as well as organ-specific conditions that influence cancer cell growth. -Cancer cells leave the bloodstream and enter particular organs, where they establish new metastatic tumors.

Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor on target cells is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine. Which statements are true about the binding of histamine to the histamine H1 receptor? Select all that apply.

-Histamine binds extracellulary to the H1 receptor -When histamine binds to the H1 receptor, the receptor undergoes a conformation change and binds the inactive G protein -Once the G protein is active, it binds the enzyme phospholipase C, activating it -Histamine is likely hydrophilic When histamine encounters a target cell, it binds extracellularly to the H1 receptor, causing a change in the shape of the receptor. This change in shape allows the G protein to bind to the H1 receptor, causing a GTP molecule to displace a GDP molecule and activating the G protein. The active G protein dissociates from the H1 receptor and binds to the enzyme phospholipase C, activating it. The active phospholipase C triggers a cellular response. The G protein then functions as a GTPase and hydrolyzes the GTP to GDP. The G protein dissociates from the enzyme and is inactive again and ready for reuse.

A current focus of molecular medicine is to trigger or prevent apoptosis in specific cells. Several components of the apoptotic pathway are being targeted using this approach. For each of the following, state specifically how the treatment would be expected to stimulate or inhibit apoptosis. Cells are treated with a small molecule called pifithrin-α, which was originally isolated for its ability to reversibly block p53-dependent transcriptional activation.

-In such cells, apoptosis would be less likely to occur, and they would be more likely to divide. -Puma would not be expressed, leading to more efficient inhibition of mitosis. -p21 would not be expressed, leading to loss of cell cycle arrest.

Describe the three main stages involved in metastasis, including a description of the relevant cellular properties. Describe the second stage involved in metastasis. Select the two correct statements.

-Only a tiny fraction of the cancer cells that enter the bloodstream survive the trip and establish successful metastases. -During the second step, the cancer cells are transported by the circulatory system throughout the body.

Cell signaling involves converting extracellular signals to specific responses inside the target cell. Different molecules are involved at each stage of the process. In this activity, you will sort items based on which stage they are involved in: reception, transduction, or response.

-Reception: G protein-coupled receptor, receptor tyrosine kinase, signaling molecule -Transduction: phosphorylation cascade, second messenger, adenylyl cyclase, Ca2+, cAMP, IP3 -Response: protein synthesis Receptor proteins (located in the plasma membrane or inside the cell) bind signaling molecules. The reception of the signal causes a shape change in the receptor molecule, to which other molecules inside the cell respond. The message is then relayed through signal transduction, which may involve a phosphorylation cascade or second messengers such as cAMP, Ca2+, or IP3. Possible responses to the signal may include synthesis of a particular protein or regulation of a particular enzyme

Describe the three main stages involved in metastasis, including a description of the relevant cellular properties. Describe the first stage involved in metastasis. Select the two correct statements.

-The first step is facilitated by decreased cell-cell adhesion, increased motility, and secretion of proteases that degrade the extracellular matrix and basal lamina. -Cancer cells invade surrounding tissues and penetrate through the walls of lymphatic and blood vessels, thereby gaining access to the bloodstream.

Describe two pieces of evidence supporting the idea that cancer cells secrete molecules that stimulate angiogenesis. Select the two correct statements.

-When cancer cells are placed in a chamber surrounded by a filter possessing tiny pores that cells cannot pass through, and the chamber is then implanted into animals, new capillaries proliferate in the surrounding host tissue. Since the cancer cells cannot pass through the filter, the most straightforward interpretation is that the cells produce molecules that diffuse through the tiny pores in the filter and activate angiogenesis in the surrounding normal tissue. -Cancer cells produce and secrete angiogenesis-activating proteins called vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF), which bind to receptor proteins on the surface of endothelial cells. The activated endothelial cells then organize into hollow tubes that develop into new blood vessels.

The histamine H1 receptor is one of several existing histamine G protein-coupled receptors. Depending on many factors, including the type of receptor, histamine can trigger a variety of responses, including vasodilation, smooth muscle contraction, stimulation of gastric secretion, cardiac stimulation, and increased vascular permeability (causing runny nose and watery eyes). Which of the following could account for the different cellular responses to histamine? Select all that apply.

-the cell type in which the histamine receptor is located -the type of second messengers involved in the signal transduction pathway -the types of relay molecules within the cell -the enzyme that is activated by the G protein associated with the receptor When histamine binds to a histamine receptor, the specific cellular response that results is determined by the following factors: -the type of histamine receptor -the type of cell in which the receptor is located -the enzyme that is activated by the G protein associated with the receptor -the types of second messengers involved in the signal transduction pathway -the proteins activated by the second messengers Signaling molecules can trigger a multitude of cellular responses, which may ultimately affect the transcription of genes, the activity of proteins, or cell growth and division.

The mitotic index is a measure of the mitotic activity of a population of cells. It is calculated as the percentage of cells in mitosis at any one time. Assume that upon examining a sample of 1000 cells, you find 30 cells in prophase, 20 in prometaphase, 20 in metaphase, 10 in anaphase, 20 in telophase, and 900 in interphase. Of those in interphase, 400 are found (by staining the cells with a DNA-specific stain) to have X amount of DNA, 200 to have 2X, and 300 cells to be somewhere in between. Autoradiographic analysis indicates that the G2 phase lasted 4 hours. What is the actual amount of time (in hours) spent in each of the phases of part B?

0.6 h in prophase; 0.4 h each in prometaphase, metaphase, and telophase; 0.2 h in anaphase; 8 h in G1; 6 h in S; and 4 h in G2.

Cortisol is a steroid hormone that can pass through the plasma membrane. Complete the flowchart describing the interaction of cortisol with intracellular receptors.

1. Cortisol passes through the plasma membrane into the cytoplasm. 2. Cortisol-receptor complex forms in the cytoplasm. 3. Cortisol-receptor complex enters the nucleus where it binds to genes. 4. Cortisol-receptor complex acts as a transcription factor 5. The transcribed mRNA is translated into a specific protein. Cortisol is a small, hydrophobic steroid hormone that can pass through the plasma membrane of cells. In target cells, cortisol binds to the intracellular receptor protein in the cytoplasm, forming a hormone-receptor complex. The hormone-receptor complex then moves into the nucleus and acts as a transcription factor, binding to specific genes and activating their transcription into mRNA. The mRNA that is produced is eventually translated into specific proteins. Proteins produced in response to the cortisol signal function in the stress response. For example, some of these proteins aid in elevating glucose levels in the blood, helping an animal to meet the demands of starvation or intense physical activity

As in most areas of biology, the study of mitosis and the cell cycle involves a lot of new terminology. Knowing what the different terms mean is essential to understanding and describing the processes occurring in the cell.

1. DNA replication produces two identical DNA molecules, called sister chromatid(s), which separate during mitosis. 2. After chromosomes condense, the centromere(s) is the region where the identical DNA molecules are most tightly attached to each other. 3. During mitosis, microtubules attach to chromosomes at the kinetochore(s). 4. In dividing cells, most of the cell's growth occurs during interphase. 5. The mitotic spindle(s) is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division. 6. During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called chromatin. 7. In most eukaryotes, division of the nucleus is followed by cytokinesis, when the rest of the cell divides. 8. The centrosome(s) are the organizing centers for microtubules involved in separating chromosomes during mitosis. The key structures involved in mitosis are labeled in this diagram of an animal cell that shows the two sister chromatids of each duplicated chromosome beginning to attach to the mitotic spindle by means of their kinetochores. The centrosomes anchor the mitotic spindle at opposite ends of the cell.

The mitotic spindle consists of two types of microtubules: kinetochore microtubules and nonkinetochore microtubules. In animal cells, these two types of microtubules function differently in the stages of mitosis. Complete the sentences by dragging the terms to the appropriate locations. Terms may be used once, more than once, or not at all.

1. During prophase, the microtubules of the mitotic spindle lengthen. 2. During anaphase, the nonkinetochore microtubules lengthen and move past each other, and the kinetochore microtubules shorten. 3. During telophase, the nonkinetochore microtubules disassemble. The mitotic spindle is the machinery that guides the separation of chromosomes in anaphase. -Prior to metaphase, the mitotic spindle is constructed by lengthening microtubules that extend from each centrosome. -In metaphase, the kinetochore microtubules have attached each pair of sister chromatids, and the nonkinetochore microtubules overlap extensively at the metaphase plate. -During anaphase, the kinetochore microtubules shorten as the chromosomes move toward the poles of the cell. At the same time, the nonkinetochore microtubules lengthen and push past each other, elongating the cell. -By the end of telophase, all the microtubules associated with the mitotic spindle have disassembled.

Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine. Complete the flowchart showing the process of histamine signal transduction from the H1 receptor.

1. Enzyme cleaves PIP2, forming DAG and IP3. 2. IP3 binds to a ligand-gated ion channel in the ER membrane. 3. Calcium ions flow through the ligand-gated ion channel. 4. Calcium ion concentration increases in the cytosol. 5. Calcium ions activate a protein, leading to a cellular response. After the reception of the histamine signaling molecule, the active G protein activates the enzyme phospholipase C. Phospholipase C cleaves PIP2 into DAG and IP3. IP3 diffuses through the cytosol and binds to an IP3-gated calcium channel in the ER membrane, causing it to open. As a result, Ca2+ ions flow out of the ER and into the cytosol. The increase in the calcium ion concentration in the cytosol helps activate the cellular response. Signal transduction pathways that involve phosphorylation cascades or multiple second messengers, such as histamine's signal transduction pathway, enable a signal to be amplified and regulated at different points. Similarly, multistep pathways can facilitate the coordination of cellular responses to multiple signals.

When mitotic Cdk-cyclin is injected into cells that have just emerged from S phase, chromosome condensation and nuclear envelope breakdown occur immediately, rather than after the normal G2 delay of several hours.

1. Mitotic Cdk-cyclin catalyzes the phosphorylation of condensins and lamins. 2. Phosphorylation of condensins and lamins contributes to chromosome condensation and nuclear envelope breakdown. 3. It is possible to trigger chromosome condensation and nuclear envelope breakdown prematurely by experimentally introducing mitotic Cdk-cyclin into cells that have just emerged from S phase. 4. Mitotic Cdk-cyclin is normally activated at the end of G2.

Consider an animal cell in which motor proteins in the kinetochores normally pull the chromosomes along the kinetochore microtubules during mitosis. Suppose, however, that during metaphase, this cell was treated with an inhibitor that blocks the function of the motor proteins in the kinetochore, but allows the kinetochore to remain attached to the spindle. The inhibitor has no effect on any other mitotic process, including the function of the nonkinetochore microtubules. Consider three questions concerning the animal cell that has been treated with the inhibitor. Drag the terms to answer the questions. Terms may be used once, more than once, or not at all.

1. Will this cell elongate during mitosis? -yes 2. Will the sister chromatids separate from each other? -yes 3. Will the chromosomes move to the poles of the cell? -no The inhibitor does not affect the cleavage of cohesins (the proteins that hold the sister chromatids together), the attachment of the chromosomes to the kinetochore microtubules, or the elongation of the cell due to the nonkinetochore microtubules. The inhibitor only affects the motor protein that pulls the chromosome along the kinetochore microtubule in anaphase. Thus, in the treated cell, the sister chromatids can still separate at the beginning of anaphase due to the fact that the cell is elongating (the centrosomes at the poles of the cell are moving farther apart) and the kinetochore microtubules still connect the chromosomes to the centrosomes. However, because the chromosomes cannot move along the kinetochore microtubules, they will never reach the poles of the cell.

The mitotic index is a measure of the mitotic activity of a population of cells. It is calculated as the percentage of cells in mitosis at any one time. Assume that upon examining a sample of 1000 cells, you find 30 cells in prophase, 20 in prometaphase, 20 in metaphase, 10 in anaphase, 20 in telophase, and 900 in interphase. Of those in interphase, 400 are found (by staining the cells with a DNA-specific stain) to have X amount of DNA, 200 to have 2X, and 300 cells to be somewhere in between. Autoradiographic analysis indicates that the G2 phase lasted 4 hours. What is the mitotic index for this population of cells?

10%

The mitotic index is a measure of the mitotic activity of a population of cells. It is calculated as the percentage of cells in mitosis at any one time. Assume that upon examining a sample of 1000 cells, you find 30 cells in prophase, 20 in prometaphase, 20 in metaphase, 10 in anaphase, 20 in telophase, and 900 in interphase. Of those in interphase, 400 are found (by staining the cells with a DNA-specific stain) to have X amount of DNA, 200 to have 2X, and 300 cells to be somewhere in between. Autoradiographic analysis indicates that the G2 phase lasted 4 hours. What is the total length of the cell cycle?

20hrs

The mitotic index is a measure of the mitotic activity of a population of cells. It is calculated as the percentage of cells in mitosis at any one time. Assume that upon examining a sample of 1000 cells, you find 30 cells in prophase, 20 in prometaphase, 20 in metaphase, 10 in anaphase, 20 in telophase, and 900 in interphase. Of those in interphase, 400 are found (by staining the cells with a DNA-specific stain) to have X amount of DNA, 200 to have 2X, and 300 cells to be somewhere in between. Autoradiographic analysis indicates that the G2 phase lasted 4 hours. Specify the proportion of the cell cycle spent in each of the following phases: prophase, prometaphase, metaphase, anaphase, telophase, G1, S, and G2.

3% of time in prophase, 2% in prometaphase, 2% in metaphase, 1% in anaphase, 2% in telophase, 40% in G1, 30% in S, and 20% in G2.

The chemical substance 2-acetylaminofluorene (AAF) causes bladder cancer when injected into rats but not guinea pigs. If normal bladder cells obtained from rats and guinea pigs are grown in culture and exposed to AAF, neither are converted into cancer cells. How can you explain these findings?

AAF is a "precarcinogen" that needs to be metabolically activated before it can cause cancer. Rats, but not guinea pigs, contain a liver enzyme that catalyzes the metabolic activation of AAF.

What would be a possible result if cells under-expressed Mad or Bub proteins?

APC would be inappropriately activated and chromatids not attached to the spindle could separate, resulting in non-disjunction.

What is the relationship between ATP and cAMP?

ATP is converted into cAMP by adenylate cyclase A cyclase is an enzyme that produces a cyclic compound. In this cause, adenylate cyclase breaks phosphorous-oxygen bonds in adenosine triphosphate (ATP), releasing pyrophosphate (also called diphosphate) and producing cyclic adenosine monophosphate (cAMP).

The mitotic index is a measure of the mitotic activity of a population of cells. It is calculated as the percentage of cells in mitosis at any one time. Assume that upon examining a sample of 1000 cells, you find 30 cells in prophase, 20 in prometaphase, 20 in metaphase, 10 in anaphase, 20 in telophase, and 900 in interphase. Of those in interphase, 400 are found (by staining the cells with a DNA-specific stain) to have X amount of DNA, 200 to have 2X, and 300 cells to be somewhere in between. Autoradiographic analysis indicates that the G2 phase lasted 4 hours. What proportion of the interphase cells would you expect to exhibit labeled nuclei in autoradiographs prepared shortly after exposure to the labeled thymidine? (Assume a labeling period just long enough to allow the thymidine to get into the cells and begin to be incorporated into DNA.)

About 30%, because all cells in S phase will incorporate label immediately, and on the average about 30% of the cells in the culture should be in S phase at any one time.

What similarities are there at the molecular level between how cells regulate the rate of GTP hydrolysis by the catalytically active portion of a heterotrimeric G protein and by Ras?

Activation of heterotrimeric G proteins involves a conformational change in a protein with which it associates. Ras activation is stimulated by a conformational change in a guanine nucleotide exchange factor (GEF), such as SOS. Regulator of G protein signaling (RGS) proteins increases the rate of hydrolysis of GTP by heterotrimeric G proteins, leading to their inactivation. These are similar to GTPase activating proteins (GAPs), which increase the rate of Ras inactivation.

Each of the following is a cancer a cancer screening procedure except colonoscopy mammography PSA test Pap smear All are screening procedures

All are screening procedures.

The chemical substance 2-acetylaminofluorene (AAF) causes bladder cancer when injected into rats but not guinea pigs. If normal bladder cells obtained from rats and guinea pigs are grown in culture and exposed to AAF, neither are converted into cancer cells. Does your explanation suggest how to predict whether AAF is carcinogenic in humans without actually exposing humans to AAF?

Analyzing human liver cells to see if they contain the activating enzyme would indicate whether AAF is likely to be carcinogenic in humans.

Children with xeroderma pigmentosum usually cannot carry out excision repair. Why was the word "usually" included in the first sentence? Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Terms can be used once, more than once, or not at all.

Because inherited mutations in the gene coding for DNA polymerase η cause a variant form of xeroderma pigmentosum in which excision repair remains intact. DNA polymerase η is a special form of DNA polymerase that catalyzes the translesion synthesis of a new, error-free stretch of DNA across regions in which the template strand is damaged. So inherited defects in DNA polymerase η, like inherited defects in excision repair, hinder the ability to repair pyrimidine dimers.

Botulinum toxin blocks neuromuscular transmission, causing paralysis. How does it do this?

Botulinum toxin cleaves the t-SNARE, blocking fusion of the vesicle.

A current focus of molecular medicine is to trigger or prevent apoptosis in specific cells. Several components of the apoptotic pathway are being targeted using this approach. For each of the following, state specifically how the treatment would be expected to stimulate or inhibit apoptosis. Treatment of cells with organic compounds that enter the cell and bind with high affinity to the active site of caspase-3.

Caspase-3 is a key activator of the apoptosis pathway, so inhibiting it would suppress cell death.

Different chemotherapeutic drugs can do each of the following except

Chemotherapeutic drugs can do all of the above.

For each of the following pairs of phases from the cell cycle, indicate how you could tell in which of the two phases a specific cell is located. G1 and M

Chromosomes are in an extended form during G1, but in a condensed form during most of M phase.

For each of the following pairs of phases from the cell cycle, indicate how you could tell in which of the two phases a specific cell is located. G2 and M

Chromosomes are in an extended form during G2, but in a condensed form during most of M phase.

Which of these is NOT correct?

Cyclic AMP binds to calmodulin. (Hint:Calcium binds to calmodulin)

For each of the following pairs of phases from the cell cycle, indicate how you could tell in which of the two phases a specific cell is located. G1 and S

DNA is being synthesized during S; little or no synthesis occurs during G1.

Which of the following will decrease the level of cAMP?

Decrease the activity of adenylate cyclase cAMP is produced from ATP by the enzyme adenylate cyclase. Increasing the level of ATP will increase the level of cAMP. Decreasing the activity of adenylate cyclase will decrease the level of cAMP. Decreasing the activity of phosphodiesterase will slow the breakdown of cAMP to AMP. This will increase the level of cAMP.

When an abnormal, indestructible form of mitotic cyclin is introduced into cells, they enter into mitosis but cannot emerge from it and reenter G1 phase.

Destruction of mitotic cyclin - and hence the inactivation of mitotic Cdk - are required before cells can complete mitosis and begin a new cell cycle.

Unlike steroid hormones, signaling molecules that are large and/or hydrophilic cannot pass through the cell's plasma membrane and therefore must bind extracellularly to receptor molecules in the plasma membrane. Two types of signal receptors embedded in the cell's plasma membrane are G protein-coupled receptors and receptor tyrosine kinases. Classify each phrase by whether it applies to G protein-coupled receptors only, receptor tyrosine kinases only, both receptors, or neither receptor.

G protein-coupled receptors: -interact directly with G proteins Receptor tyrosine kinases: -catalyzes the transfer of a phosphate group to the receptor -binding of the signaling molecule forms a dimer Both: -binding site for signaling molecule is located on the extracellular side of the cell -receptor is located in the plasma membrane Neither: -binding of the signaling molecule allows ions to flow through a channel in the receptor Both G protein-coupled receptors and receptor tyrosine kinases are transmembrane receptors that have a binding domain located on the extracellular side of the plasma membrane. The binding of a signaling molecule to these receptors is the first step in a signaling pathway. However, what happens after a signaling molecule binds is different for each receptor. An activated G protein-coupled receptor activates a G protein inside the cell, which involves the release of GDP and the binding of GTP. The activated G protein then activates an associated enzyme, leading to a cellular response. Receptor tyrosine kinases form dimers after binding signaling molecules. The tyrosines are then phosphorylated, fully activating the receptor. Each phosphorylated tyrosine can bind a relay protein, each of which can trigger a transduction pathway. In this way, a single signaling-molecule binding event can trigger multiple signal transduction pathways and thus multiple cellular responses.

A researcher generates a mutant cell line in a laboratory culture in which the mutants have an RGS-GAP that is increased in activity. What is the likely outcome of this mutation?

G protein-mediated cellular signaling will terminate faster.

A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors.

G-protein-linked GTP activates G proteins.

Epinephrine acts as a signal molecule that attaches to _____ proteins.

G-protein-linked receptor Epinephrine acts via G-protein-linked receptors.

For each of the following pairs of phases from the cell cycle, indicate how you could tell in which of the two phases a specific cell is located. G1 and G2

G1 has the 2C amount of DNA; G2 has the 4C amount

As the chromosomes of a parent cell are duplicated and distributed to the two daughter cells during cell division, the structure of the chromosomes changes. Answer the three questions for each phase of the cell cycle by dragging the yes and no labels to the appropriate locations in the table. Note: Assume that by the end of the M phase, the parent cell has not yet divided to form two daughter cells. -DNA condensed in all or part of phase?

G1-no S-no G2-no Beginning of M-yes End of M-yes Sister chromatids form when DNA replicates in the S phase. The sister chromatids become individual chromosomes once they separate in early anaphase. Similarly, the cellular DNA content doubles in the S phase when the DNA replicates. However, the cell's DNA content does not return to its normal (undoubled) levels until after cytokinesis is complete and two daughter cells have formed. The condensation state of the DNA is not related to the presence or absence of sister chromatids. The DNA condenses in prophase and remains condensed until after the sister chromatids separate and the new daughter cells begin to form. In late telophase/cytokinesis, the emphasis shifts to cell growth and DNA replication for the next cell cycle. For these processes to occur, the DNA needs to be de-condensed so it is accessible to the cellular machinery involved in transcription.

As the chromosomes of a parent cell are duplicated and distributed to the two daughter cells during cell division, the structure of the chromosomes changes. Answer the three questions for each phase of the cell cycle by dragging the yes and no labels to the appropriate locations in the table. Note: Assume that by the end of the M phase, the parent cell has not yet divided to form two daughter cells. -Sister chromatids present in all or part of phase?

G1-no S-yes G2-yes Beginning of M-yes End of M-no Sister chromatids form when DNA replicates in the S phase. The sister chromatids become individual chromosomes once they separate in early anaphase. Similarly, the cellular DNA content doubles in the S phase when the DNA replicates. However, the cell's DNA content does not return to its normal (undoubled) levels until after cytokinesis is complete and two daughter cells have formed. The condensation state of the DNA is not related to the presence or absence of sister chromatids. The DNA condenses in prophase and remains condensed until after the sister chromatids separate and the new daughter cells begin to form. In late telophase/cytokinesis, the emphasis shifts to cell growth and DNA replication for the next cell cycle. For these processes to occur, the DNA needs to be de-condensed so it is accessible to the cellular machinery involved in transcription.

As the chromosomes of a parent cell are duplicated and distributed to the two daughter cells during cell division, the structure of the chromosomes changes. Answer the three questions for each phase of the cell cycle by dragging the yes and no labels to the appropriate locations in the table. Note: Assume that by the end of the M phase, the parent cell has not yet divided to form two daughter cells. -DNA content per cell doubled in all or part of phase?

G1-no S-yes G2-yes Beginning of M-yes End of M-yes Sister chromatids form when DNA replicates in the S phase. The sister chromatids become individual chromosomes once they separate in early anaphase. Similarly, the cellular DNA content doubles in the S phase when the DNA replicates. However, the cell's DNA content does not return to its normal (undoubled) levels until after cytokinesis is complete and two daughter cells have formed. The condensation state of the DNA is not related to the presence or absence of sister chromatids. The DNA condenses in prophase and remains condensed until after the sister chromatids separate and the new daughter cells begin to form. In late telophase/cytokinesis, the emphasis shifts to cell growth and DNA replication for the next cell cycle. For these processes to occur, the DNA needs to be de-condensed so it is accessible to the cellular machinery involved in transcription.

Based on the graph, how long does it take for maximal Ras activation to be achieved?

It takes approximately 1.5−2 min to reach maximal Ras activation.

Which of the following outcomes would you expect to see if Ras were to acquire a mutation in which its GTPase activity were abolished?

MAP kinases will be continuously activated, promoting continual and repeating mitotic divisions.

Cancer cell aneuploidy (the gain or loss of chromosomes) is most likely caused by a defect in

Mad

Imagine that you are a graduate student working in a cancer lab. You accidentally mix unlabeled tubes of carcinoma cells with tubes of normal epithelial cells. Which of the following is NOT a possible strategy to allow you to distinguish which tubes contain carcinoma cells?

Monitor the rate of cell division.

You are given two test tubes, one containing cells from a human cancer and the other containing normal cells. Before you begin your studies, the labels fall off the test tubes. How could you determine which sample contains the cancer cells? Sort each test results into the appropriate bin.

Normal Cells: -need anchorage for growth -don't divide more than 50-60 times in culture Cancer Cells: -have mechanisms for replenishing their telomeres in culture -grow well in culture -grow to higher population densities in culture -produce tumors being injected into nude mice

Phosphorylated p53 can act as a transcription factor. When there is major damage to the genome, p53 increases the transcrption of which gene?

PUMA

Neutrophils are blood cells normally responsible for killing bacteria at sites of infection. Neutrophils are able to find their way toward sites of infection by the process of chemotaxis. In this process, neutrophils sense the presence of bacterial proteins and then follow the trail of these proteins toward the site of infection. Suppose you find that chemotaxis is inhibited by pertussis toxin. What kind of receptor is likely to be involved in responding to bacterial proteins?

Pertussis toxin ADP ribosylates certain G proteins. It would be likely that a neutrophil responds to bacterial proteins through a G protein-linked receptor.

Mitosis unfolds through a sequence of stages marked by specific events in the cell. The structural changes in the cell are brought about by a series of tightly coordinated underlying mechanisms. Sort each process into the appropriate bin to indicate the stage of mitosis in which it occurs. If a process occurs in more than one stage, sort it to the stage when it first occurs.

Prophase: -Cohesions join sister chromatids of duplicated chromosome -Tubulins assemble into spindle microtubules Prometaphase: -Microtubules attach to kinetochores Metaphase: -Kinetochores are motionless in relation to poles of cell Anaphase: -Cohesins break down -Kinetochores move toward poles of cell Telophase: -Spindle microtubules disassemble The micrographs in Part A show some of the cellular processes that occur during the stages of mitosis. -In prophase, the microtubules of the spindle apparatus begin to assemble from individual tubulin subunits. As the identical chromatids of each pair of sister chromatids condense during this stage, they are held together by cohesin proteins. -Prometaphase is marked by fragmentation of the nuclear envelope, expansion of the spindle into the nuclear region, and attachment of some spindle fibers to the chromosomes via the kinetochores. -Metaphase, marked by the alignment of chromsomes along the metaphase plate, is brought about by kinetochores aligning and then remaining motionless relative to the poles of the cell. -In anaphase, the cohesin proteins are cleaved, and the kinetochores move toward the poles of the cell, separating the sister chromatids. -As telophase proceeds, the kinetochore microtubules of the spindle disassemble. As the chromosomes reach the poles of the cell, the nuclear envelopes of the two new daughter nuclei form.

Why do you suppose that the concentration of p53 is controlled by its degradation rather than at the level of its transcription like many other proteins?

Protection from degradation allows for a much faster build up in response to changes in cellular conditions.

Mutations that inactivate the main protein phosphatase used to catalyze protein dephosphorylations cause a long delay in the reconstruction of the nuclear envelope that normally takes place at the end of mitosis.

Proteins phosphorylated by mitotic Cdk-cyclin at the beginning of prophase must be dephosphorylated again before cells can finish mitosis

Children with xeroderma pigmentosum usually cannot carry out excision repair. Why does this makes them so susceptible to developing cancer?

Pyrimidine dimers caused by exposure to sunlight can create mutations that lead to cancer, and one of the main mechanisms for repairing such defects is excision repair.

What is the role of Rab GTPase in the process?

Rab GTPase locks the t-SNARE and v-SNARE together, facilitating fusion of the vesicle.

Why does Ras activity decline after a few minutes, even when EGF is still present?

Ras activity gradually decreases due to the action of Ras GAPs, which stimulate Ras to hydrolyze GTP to GDP, inactivating Ras.

A person who smokes for the first time tends to experience much more severe effects from a cigarette than does someone who smokes frequently. Given that the smoke contains nicotine, provide a reasonable explanation for this difference.

Smokers do develop tolerance to nicotine. Therefore, it would be reasonable to suggest that chronic exposure to nicotine might lead to receptor down-regulation as a basis for this tolerance.

A current focus of molecular medicine is to trigger or prevent apoptosis in specific cells. Several components of the apoptotic pathway are being targeted using this approach. For each of the following, state specifically how the treatment would be expected to stimulate or inhibit apoptosis. Exposing cells to recombinant TRAIL protein, a ligand for the tumor necrosis factor family of receptors.

TRAIL would activate pathways similar to TNF-α, a known stimulator of apoptosis.

The annual incidence of colon cancer in the United States is about 55 cases per 100,000. Because colon cancer often causes bleeding, doctors sometimes use a screening procedure called the fecal occult blood test (FOBT) to look for tiny amounts of blood in the feces. One form of this test has a specificity of about 98%, which means that when it indicates the presence of blood in the feces, the result is an error (i.e., cancer is not present) only 2% of the time. While this may seem like excellent specificity, a 2% "false positive" rate makes this test almost useless as a tool for colon cancer screening. Why is this test almost useless as a tool for colon cancer screening?

Testing 100,000 people, the 2% false positive rate yields many more incorrect results (2,000) compared to real cancer cases (55).

G protein-linked receptors interact with heterotrimeric G proteins to activate them. Upon binding to the receptor, the Gβγ subunit catalyzes GDP/GTP exchange by the Gα subunit. How is this similar to the activation of Ras by a receptor tyrosine kinase?

The activation of Ras requires the assistance of another protein called SOS. Upon binding to the tyrosine kinase receptor, SOS catalyzes the RasGDP/GTP exchange reaction. In this respect, SOS and Ras together are similar to a heterotrimeric G protein. Here, SOS acts like the Gβγ subunits, whereas Ras is similar to a Gα subunit.

Hypertension, or high blood pressure, is often seen in elderly people. A typical prescription to reduce a patient's blood pressure includes compounds called beta-blockers, which block β-adrenergic receptors throughout the body. Why do you think beta-blockers are effective in reducing blood pressure?

The binding of epinephrine to beta-adrenergic receptors causes a stimulation of heart function, both in terms of heart rate and with respect to the amount of work done in pumping blood. The effect appears to be mediated by cyclic AMP. When an antagonist such as the beta blocker propranolol is given to patients with hypertension, the cellular response caused by the binding of epinephrine to beta receptors is partially inhibited. Heart function is gradually restored over a period of time, with a corresponding decrease in blood pressure.

A mutant cell line is produced in which a motor protein specific for astral microtubules is inactivated. Which of these statements accurately describes the status of the cells and functional consequence of the mutation?

The cells will be stuck in anaphase because the astral motor proteins cannot help pull the spindle to the spindle poles.

Using these tools, describe how you could demonstrate that a hormone exerts its effect by (1) causing Ca2+ to enter the cell through channels or (2) releasing Ca2+ from intracellular stores such as the ER.

The chelator could be added to the extracellular medium to reduce the calcium levels outside the cell. Addition of the chelator to the extracellular medium should block the action of the hormone if it depends on calcium influx. If the action of the hormone depends solely on calcium release from intracellular stores, then addition of a calcium ionophore should mimic the action of the hormone. In this case, the ionophore should be effective even when EGTA is added to the extracellular medium to reduce the free calcium ion concentration.

What would be the effect of adding colchicine to cells that were at the metaphase-anaphase transition?

The chromosomes would segregate but the cell would not elongate.

The mitotic index is a measure of the mitotic activity of a population of cells. It is calculated as the percentage of cells in mitosis at any one time. Assume that upon examining a sample of 1000 cells, you find 30 cells in prophase, 20 in prometaphase, 20 in metaphase, 10 in anaphase, 20 in telophase, and 900 in interphase. Of those in interphase, 400 are found (by staining the cells with a DNA-specific stain) to have X amount of DNA, 200 to have 2X, and 300 cells to be somewhere in between. Autoradiographic analysis indicates that the G2 phase lasted 4 hours. To measure the G2 phase, radioactive thymidine (a DNA precursor) is added to the culture at some time t, and samples of the culture are analyzed autoradiographically for labeled nuclei at regular intervals thereafter. What specific observation would have to be made to assess the length of the G2 phase?

The first appearance of label in prophase nuclei would have to be observed.

Which of the following would be expected if a researcher added an inhibitor of cyclin-dependent kinases (Cdk) at the end of prophase and beginning of prometaphase?

The nuclear envelope would not break down.

Autophosphorylation is an important part of the mechanism of the receptor tyrosine kinases. Why is this?

The phosphorylation provides sites for recruitment of other signal transduction molecules.

You are an epidemiologist/pathologist working in a lab analyzing tissue samples. An oncologist brings two biopsies of two different tumors from the same patient. She would like to know which tumor is more malignant and requires more aggressive and timely treatment. Which of the following morphological features of the biopsies will dictate which tumor is more malignant?

The tumor with a high nucleus-to-cytoplasm ratio should require more aggressive and timely treatment.

What activity do APC and Mdm2 share

They are ubiquitin ligases

Which of the following is NOT true of both ATP and cAMP?

They both have the same number of ring structures Both ATP and cAMP contain the nitrogenous base adenine, and the sugar ribose. ATP has three linearly connected phosphate groups. cAMP has only one phosphate group that is attached to both the 3' and 5' carbons of the ribose sugar to form a cyclic phosphate ring structure.

Many chemicals are more mutagenic after being processed in the liver.

True Many potential mutagens are poorly mutagenic until passing through the liver.

The anti-angiogenic drug Avastin works by binding to and inhibiting the activity of

VEGF

Consider the mechanism of Botulinum toxin. Is this toxin reversible?

Yes, however the cell must regenerate new t-SNAREs.

The cell cycle represents the coordinated sequence of events in the life of a cell from its formation to its division into two daughter cells. Most of the key events of the cell cycle are restricted to a specific time within the cycle. In this exercise, you will identify when various events occur during the cell cycle. Recall that interphase consists of the G1, S, and G2 subphases, and that the M phase consists of mitosis and cytokinesis.

a - non-dividing cells exit cell cycle b - at this point, cell commits to go through cycle c - DNA replicates d - Centrosome replicates e - Mitotic spindle begins to form f - cell divides, forming two daughter cells Many organisms contain cells that do not normally divide. These cells exit the cell cycle before the G1 checkpoint. Once a cell passes the G1 checkpoint, it usually completes the cell cycle--that is, it divides. -The first step in preparing for division is to replicate the cell's DNA in the S phase. -In the G2 phase, the centrosome replicates. -In early M phase, the centrosomes move away from each other toward the poles of the cell, in the process organizing the formation of the mitotic spindle. -At the end of the M phase when mitosis is complete, the cell divides (cytokinesis), forming two genetically identical daughter cells.

Receptor tyrosine kinases are activated by hormones that cause cell division (mitogens). Which of the following describes a way that a protein in the pathway could be mutated to result in its constitutive activation causing unregulated cell division?

a mutation in Ras that makes it unable to hydrolyze GTP

Which of these is NOT an example of the protein product of an oncogene?

a tumor suppressor

Which of the following would be a histological indicator of a pre-cancerous or cancerous state in intestinal epithelial cells?

accumulation of beta-catenin in the nucleus of the colon epithelium

Which of the following experimental strategies could be used to block the IP3 branch but not the DAG branch of the IP3 pathway?

adding an antagonist of the IP3 receptor

cAMP is an abbreviation for

adenosine 3',5'-cyclic monophosphate cAMP is a adenine nucleotide. It contains one phosphate group esterified to the 3' and 5' carbons of the ribose sugar. Its chemical name is adenosine 3',5'-cyclic monophosphate.

Which microtubules shrink during mitosis?

astral and kinetochore microtubules

The molecular motors that are most active in Prophase are the ones attached to __________.

astral microtubules

Which of the following reactions is catalyzed by a phosphodiesterase?

cAMP converted to AMP Phosphodiesterases (PDEs) are a class of enzymes that break phosphodiester bonds. PDE hydrolyzes the 3' phosphodiester bond of adenosine 3',5' cyclic monophosphate (cAMP) to produce adenosine 5'-monophosphate (AMP).

Match the second messenger with the properties.

cAMP:glucose mobilization IP3:opens calcium ion channels DAG:activated protein kinase C Calcium:binds to calmodulin cGMP:smooth muscle relaxation

Which of these is activated by calcium ions?

calmodulin Calmodulin is a calcium-binding protein.

Hormones that use the tyrosine kinase receptor mechanism as shown in the animation are important for

cellular growth and survival

Which protein holds the sister chromatids together?

cohesions

The cleavage of glycogen by glycogen phosphorylase releases _____.

glucose-1-phosphate Glycogen is a polysaccharide composed of glucose monomers.

Which of the following is NOT a mechanism used to temporally regulate the activity of maturation-promoting factor (MPF)?

glycosylation

Sos activates Ras. Sos is an example of a

guanine-nucleotide exchange factor (GEF).

What is another likely role of the SNARE mechanism of vesicle fusion, in addition to secretion of material?

insertion of membrane proteins into the plasma membrane

The dominant negative mutation of the receptor in the animation is effective in blocking the hormone signal because

it is able to dimerize with a functional receptor without the activation of autophosphorylation.

Based on the direction of movement, the kinetochore molecular motor is most likely _____-based.

kinesin

What protein complex or complexes provide initial recognition of the vesicle with the target membrane?

multisubunit tethering proteins and coiled-coil tethering proteins

A physician using a microscope to examine suspect cells in biopsy tissue would expect to find each of the following characteristics in metastatic cancer cells except

perfectly spherical nuclei.

Which type of microtubule is responsible for the elongation of the cell in Anaphase B?

polar

In the Ames Test, the appearance of his+ revertants in the presence of a non-mutagenic control compound indicates that _______.

some of the reversion mutations are not caused by the mutagen being tested His+ revertants on the control plate are the result of spontaneous mutation.

The purpose of the Ames Test is to _______.

test the mutagenic effects of chemicals The Ames test detects whether a given chemical can cause a reversion mutation in his- bacteria.

Alpha- and beta-adrenergic receptors can bind epinephrine and norepinephrine, yet they trigger different signal transduction pathways. This is because __________.

the receptors activate different G proteins