Bio 203 Ch 12

What is the name of unreplicated DNA wrapped around globular histone proteins? a. Sister chromatids b. Chromatin c. Kinetochores d. Chromosomes

b. chromatin when DNA is unsynthesized in the G1 phase, it is called chromatin

If the cell shown in the micrographs has 60 picograms of DNA and 22 chromosomes in its G1 phase, how much DNA and how many chromosomes are in the anaphase cell? a. 120 pg of DNA; 44 chromosomes b. 60 pg of DNA; 44 chromosomes c. 120 pg of DNA; 22 chromosomes d. 60 pg of DNA; 22 chromosomes

a. 120 pg of DNA; and 44 chromosomes During prophase, the DNA was doubled from 60 to 120 pg. The anaphase cell still has 120 pg of DNA, but when chromatids separate, each is defined as a daughter chromosome, so the cell has 44 chromosomes

G1 is represented in the figure why which numbered part(s) of the cycle? a. I or V (flattened lines) b. II or IV (inc & dec first cycle) c. III only (flat line at top of first cycle) d. IV only (decline on first cycle) e. V only (flat line before second cycle)

a. I or V

Inhibiting expression of the stathmin gene arrests cells in M phase and is being investigated as an alternative therapy for treating cancer. What additional genes could be therapeutic targets that would arrest cancerous cells in G1 phase? a. Inactivating genes for G1 cyclins b. Inactivating genes for Rb c. Activating genes for E2F d. Activating genes for Cdk

a. Inactivating genes for G1 cyclins Both of these targets would allow for the arresting of cancerous cells in G1 and could therefore act as an alternative pathway

Specialized proteins called cell cycle regulators, such as p53 and p21, regulate the progression of the cell cycle from one phase to the next. This progression through the checkpoints is strictly regulated and usually works without error. When errors do occur, they can have catastrophic consequences, including cancer. How did this study lend new evidence to our understanding of how genes regulate the cell cycle, giving us a better chance of developing successful cancer treatments? a. Mutations in the p53 and p21 genes lead to checkpoint deficits, specifically the G2-M checkpoint, linked to multiple types of cancer. These checkpoint deficits can be exploited in the development of targeted treatments. b. Mutations in the p53 and p21 genes play a crucial role at the S checkpoint of the cell cycle, preventing cells with DNA damage from entering mitosis. Targeting therapies to these proteins could improve efficacy of treatment. c. All cells deficient in p53 and p21 proteins proceed to mitosis after radiation exposure, and the cells have a DNA content that differs from what would be expected. This chromosomal abnormality can be exploited in the development of targeted treatments.

a. Mutations in the p53 and p21 genes lead to checkpoint deficits, specifically the G2-M checkpoint, linked to multiple types of cancer. These checkpoint deficits can be exploited in the development of targeted treatments. According to the authors of the paper, mutations in p53 and p21 genes burden cells with a significant checkpoint deficit, especially at the G2-M checkpoint. Such checkpoint defects may be exploited to treat the many cancers resulting from abnormalities of p53 function.

The MPF protein complex turns itself off by ___. a. activating a process that destroys cyclin components b. binding to chromatin c. exiting the cell d. activating the anaphase-promoting complex e. activating an enzyme that stimulates cyclin

a. activating a process that destroys cyclin components

Although the process of chromosome partitioning during mitosis is visible through a light microscope, the process of DNA replication is not. Why? a. Chromosomes are too extended during S phase to be seen by light microscopy. b. Chromosomes form only during mitosis. c. Chromosomes are visible only after DNA has been duplicated. d. Chromosomes do not contain protein until mitosis.

a. chromosomes are too extended during S phase to be seen by light microscopy. Individual chromosomes are visible in a light microscope only after condensation, which occurs during prophase of mitosis

which of the following conditions will most likely prevent a cell prom passing the G2 checkpoint? a. Chromosomes have replicated incorrectly. b. Nutrients are adequate. c. The cell has reached a certain minimum size. d. Activated MPF is present.

a. chromosomes have replicated incorrectly DNA must be properly replicated for a cell to pass the G2 checkpoint and enter M phase. The cell would not want to replicate damaged chromosomes

Kinetochore microtubules assist in the process of splitting centromeres by ___. a. creating tension by pulling toward opposite poles b. using motor proteins to split the centromere at specific arginine residues c. phosphorylating the centromere, thereby changing its conformation d. sliding past each other like actin filaments

a. creating tension by pulling toward opposite poles

_____ is a carcinogen that promotes colon cancer. a. fat b. UV light c. estrogen d. a virus e. testosterone

a. fat a dies high in fat increases the risk of both colon and breast cancer

Mitotic spindle fibers are composed of what cellular components? a. Microtubules b. Actin c. Centrosomes d. Kinetochores

a. microtubules mitotic spindle fibers are composed of an array of microtubules that radiate from a microtubule-organizing center

During mitosis, it is necessary for the nuclear envelope of the parent cell to disintegrate. This is accomplished in part by phosphorylation of proteins associated with the nuclear envelope. If the enzyme responsible for that phosphorylation event is inhibited, at which phase of mitosis are cells likely to arrest? a. Prophase b. Telophase c. Anaphase d. Metaphase

a. prophase during prometaphase the nuclear envelope breaks down. this step is halted, arresting cells in prophase. Advancing to metaphase requires breakdown of the nuclear envelope so that mitotic spindles can attach to the chromosomes

In an experiment to determine whether cyclin protein was a required component of MPF activity, why did researchers add cyclin mRNA to immature oocyte extract? a. The cyclin mRNA would be translated into cyclin protein and increase MPF activity. b. It was expected that cyclin mRNA is a necessary component of the MPF. c. As a negative control, because they knew cyclin would inhibit the cells from entering mitosis. d. It was expected that the cyclin mRNA would have no effect.

a. the cyclin mRNA would be translated into cyclin protein and increase MPF activity

Which statement about the daughter cells following mitosis and cytokinesis is correct? a. they are genetically identical to each other and to the parent cell b. Only one of the two daughter cells is genetically identical to the parent cell. c. They are genetically different from each other and from the parent cell. d. They are genetically identical to each other but different from the parent cell

a. they are genetically identical to each other and to the parent cell the process of mitosis is the way in which cells divide to generate exact genetic copies of each other; therefore, the parents and daughters are genetically identical

Many cancers are due to the failure of cells to properly regulate the ___ checkpoint during the cell cycle. a. Cancer is not caused by the inability to regulate a checkpoint. b. G1 c. S d. G2

b. G1 Cells that have passed the G1 checkpoint are committed to replicating their DNA and dividing

The length of the different phases of the cell cycle can be measured by performing a pulse-chase experiment with radioactive thymidine and waiting to see how long it takes for radioactivity to appear in mitotic chromosomes. After the radioactivity first arrives in mitotic chromosomes, it is observed that the amount of radioactivity in these chromosomes increases steadily over several hours, reaches a plateau, and then declines. What cell-cycle phase is measured by the time between the first and last appearance of radioactive thymidine in condensed, mitotic chromosomes? a. M phase b. S phase c. G2 phase d. G1 phase

b. S phase Thymidine is incorporated into chromosomes during DAN synthesis or S phase. The first radioactive mitotic chromosomes were at the start of S phase, and the last radioactive mitotic chromosomes were at the end of S phase. Therefore, the time in between is the length of S phase.

Which of the following is the correct order for the phases of the cell cycle a. G1, G2, S, and M b. S, G2, M, and G1 c. S, G1, M, and G2 d. fS, G2, G1, and M

b. S, G2, M, G1 DNA synthesis (S phase) occurs before M (mitosis phase) with a Gap called G2 in between and G1 follows M

Large-scale cancer studies have found that the p53 gene is often mutated in tumor cells. In fact, the gene encoding the p53 protein is mutated in tumor cells more often than any of the other 20,000 human genes. Based on this information, why was the Bunz study important? a. A deeper understanding of the role of p53 in the cell cycle can improve our understanding of radiation and the damage done to DNA. b. A deeper understanding of the role of p53 in the cell cycle can improve our understanding of cancers and perhaps lead to new forms of treatment. c. A deeper understanding of the role of p53 in the cell cycle can improve our understanding of other oncogenes associated with various cancers. d. A deeper understanding of the cell cycle checkpoints can improve our understanding of how radiation damages DNA and arrests the cell cycle.

b. a deeper understanding of the role of p53 in the cell cycle can improve our understanding of cancers and perhaps lead to new forms of treatment In the last paragraph of the paper, the authors state: "Although p53 mutations provide cells with a selective growth advantage, such mutations burden them with a significant checkpoint deficit. Such checkpoint defects may be exploited to treat the many cancers with abnormalities of p53 function."

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the cell cycle would be most disputed by cytochalasin B? a. cell elongation during anaphase b. cleavage furrow formation and cytokinesisDNA synthesis c. spindle attachment to kinetochores d. spindle formation

b. cleavage furrow formation and cytokinesis

Proteins that are involved in the regulation of the cell cycle and that show fluctuations in concentration during the cell cycle are called ___. a. kinectochores b. cyclins c. ATPases d. kinases e. estrogen receptors

b. cyclins

Much of what is known about the function of cyclin and Cdk was learned by mutations in yeast. One yeast mutant is known as wee1. As its name implies, this yeast mutant never achieves full size. It divides continuously without allowing time for the cells to grow to their normal size. The defect is caused by inactivation of a gene that encodes a protein kinase. What might be a possible role for this kinase in normal wild-type yeast? a. It may degrade Cdk. b. It may phosphorylate and inhibit the activity of mitotic Cdk. c. It may phosphorylate and activate cyclin. d. It may phosphorylate and inhibit the action of the enzyme that degrades cyclin.

b. it may phosphorylate and inhibit the activity of mitotic CDK In fact, this is what the wee1 protein does. After cyclin binds to mitotic Cdk, wee1 phosphorylates CDK and inhibits it until the cell is ready to divide. At that point, an enzyme removes the phosphate from mitotic Cdk, allowing it to be active as MPF

Many cells associated with a variety of cancers have mutations in the p53 gene. Why are mutated tumor suppressor genes, like p53, considered recessive mutations? a. The wild-type p53 protein suppresses the activity of the protein derived from the mutated form of the gene. b. Loss of p53 function only occurs when both copies of the p53 gene are mutated (p53-/-). c. The wild-type p53 protein is stronger than the protein derived from the mutated form of the gene. d. Mutations in the p53 gene are harmful since they can lead to tumor formation, and all harmful mutations are recessive.

b. loss of p53 function only occurs when both copies of the p53 gene are mutated (p53-/-) When one copy of the p53 gene is mutated, the p53 protein is still made and can still halt the cell cycle. Only when both copies are "lost" is no p53 protein produced.

Taxol is a drug that stabilizes microtubules and prevents them from depolymerizing. Consequently, cells treated with taxol fail to complete mitosis. What is the last stage of mitosis that taxol-treated cells are likely to complete? a. Prophase b. Metaphase c. Telophase d. Anaphase

b. metaphase during metaphase the dominant activity of microtubules is polymerization to form mitotic spindles. To go to the next stage, anaphase, depolymerization is required

In which cell types is a cell plate present during cytokinesis? a. All cells use a cell plate during cytokinesis. b. Plant cells c. Animal cells d. Bacteria

b. plant cells the cell plant divides the cytoplasm during cytokinesis in plant cells.

The length of the different phases of the cell cycle can be measured by performing a pulse-chase experiment with radioactive thymidine and waiting to see how long it takes for radioactivity to appear in mitotic chromosomes. What cell-cycle phase is measured as the time between the end of radioactive thymidine labeling and the beginning of the appearance of radioactive mitotic chromosomes? a. G1 phase b. M phase c. G2 phase d. S phase

c. G2 phase the first labeled mitotic chromosomes appear in the cells that were just completing DNA replication when labled thymidine was added. The time from the end of S phase to the beginning of M phase corresponds to G2 phase

What would be the effect on the cell cycle of interphase frog oocytes if chromosomes from M phase oocytes were injected into them? a. The interphase oocytes would replicate their DNA. b. The interphase oocytes would immediately enter mitosis. c. Nothing would happen. d. The interphase oocytes would start mitosis and then stop before completing cell division.

c. Nothing would happen chromosomes are not the factor that stimulates mitosis

Exposure to chemicals that cause mutations in DNA greatly increases the chance of developing cancer. Mutations that inactivate which of the following proteins would most likely lead to cancer? a. Mitotic cyclin b. G1 cyclin c. Rb (retinoblastoma) protein d. Tubulin

c. Rb protein Rb normally inactivates E2F to prevent it from activating s-phase genes too soon, so inactivating this inhibitor would result in premature entry into S phase and, therefore, more rapid movement through the cell cycle

When actively growing cells are treated with Taxol, they often are unable to complete the cell cycle. Based on what you have learned about cell-cycle checkpoints, which checkpoint likely causes these cells to arrest? Explain your reasoning. a. The first MM phase checkpoint. If the sister chromatids all kinetochores are not attached properly to the spindle apparatus, then the sister chromatids do not split and the cells would arrest in MM phase.G1 b. G1 checkpoint. If the growth of the cell was blocked, or if DNA was physically damaged and cannot be repaired, then the cell would arrest in G1 c. G1 phase.The second MM phase checkpoint. If microtubule depolymerization were inhibited, the chromosomes would not completely separate in anaphase, and the cells would arrest in MM phase.G2 d. G2 checkpoint. If DNA is damaged or if chromosomes are not replicated correctly, the inhibitory phosphate on MPF's Cdk subunit won't removed. As a result, MPF is not turned on, and cells remain in G2 phase.

c. The second M phase checkpoint. If microtubule depolymerization were inhibited, the chromosomes would not completely separate in anaphase, and the cells would arrest in M phase

What role(s) do gap phases play in the cell cycle? a. They allow chromosome replication to occur. b. They allow chromosomes to condense prior to mitosis. c. They allow cells to replicate organelles and manufacture additional cytoplasm. d. They allow the nuclear envelope to re-form after mitosis.

c. They allow cells to replicate organelles and manufacture additional cytoplasm G1 and G2 phases allow the cell to complete these steps so that daughter cells produced in M phase will be normal in size and function

The G1 checkpoint prevents the replication of possible cancerous cells by use of these regulatory proteins. a. M-phase-promoting factor (MPF) b. Cyclin-dependent kinase c. Tumor suppressors d. Cyclin

c. tumor suppressors p53 is an example of a tumor suppressor that prevents cells with damaged DNA to continue through the cell cycle

A certain species of animal has 6 pairs of chromosomes. How many sister chromatids do the nuclei of these animals have during G2 phase? a. 48 b. 6 c. 12 d. 24

d. 24 DNA replication was completed during S phase, prior to G2 phase. Each chromosome (12) is replicated, so there are 24 sister chromatids

Which of the following lists the four cell-cycle checkpoints in the cell cycle in the correct order? a. M checkpoint between metaphase and anaphase, M checkpoint between anaphase and telophase, G1checkpoint, G2 checkpoint b. G1 checkpoint, G2 checkpoint, M checkpoint between anaphase and telophase, M checkpoint between metaphase and anaphase c. G2 checkpoint, G1 checkpoint, M checkpoint between metaphase and anaphase, M checkpoint between anaphase and telophase d. G1 checkpoint, G2 checkpoint, M checkpoint between metaphase and anaphase, M checkpoint between anaphase and telophase

d. G1 checkpoint, G2 checkpoint, M checkpoint between metaphase and anaphase, M checkpoint between anaphase and telophase The four checkpoints are (1) the G1 checkpoint between G1 and S; (2) the G2 checkpoint between G2 and M; (3) the first M checkpoint between metaphase and anaphase; and (4) the second M checkpoint between anaphase and telophase. Without these four checkpoints, cells could be overproduced in multicellular organisms, and cell division could result in daughter cells that are inviable or have defects in their genetic material.

Which of these is NOT a carcinogen? a. UV light b. fat c. testosterone d. cigarette smoke e. all of the above are carcinogens

d. all of the above are carcinogens all of these substances can cause cancer

The consequence of E2F inactivation is that ___. a. the Rb protein becomes activated b. cells immediately enter S phase c. cells develop cancer d. cells are unable to enter S phase

d. cells are unable to enter S phase E2F stimulates entry into S phase

One interesting experiment conducted with frog oocytes revealed that with an appropriate stimulus, the cyclic appearance and disappearance of cyclin occurs even in the absence of a nucleus. What does this result imply about the production of cyclin in oocytes during the cell cycle? a. Chromosomes are not restricted to the nucleus in frog oocytes. b. Synthesis of cyclin mRNA (transcription) occurs outside the nucleus in frog oocytes. c. Cyclin is encoded by mitochondrial DNA. d. Cyclin is synthesized using preexisting mRNA.

d. cyclin is synthesized using preexisting mRNA In fact, the synthesis of many proteins during early development of frog embryos relies on mRNA stored in the cytoplasm and, therefore, does not require a nucleus

turmor supressor genes ____. a. often encode proteins that stimulate the cell cycle b. are cancer-causing genes introduced into cells by viruses c. are frequently overexpressed in cancerous cells d. encode proteins that help prevent uncontrolled cell growth

d. encode proteins that help prevent uncontrolled cell growth

Early detection is the key to successful treatment of most cancers. Why? a. Cancer cells often do not need growth factors or other types of normal signals to grow. b. All of the listed responses are correct. c. Cancer is caused by a wide variety of different defects, many related to failure of cell-cycle checkpoints. d. If caught early enough, cells from the primary tumor are less likely to have traveled to new sites and started secondary tumors.

d. if caught early enough, cells from the primary tumor are less likely to have traveled to new sites and started secondary tumores cancer cells are prone to detach from the primary tumor and metastasize, meaning that they invade other tissues of the body. the prevention of metastasis is the main reason that early detection can lead to successful treatment of most cancers.

Use the following information to answer the question(s) below. Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and, therefore, can be assayed to track their incorporation. In a set of experiments, a studentfaculty research team used labeled T nucleotides and introduced these into the culture of dividing human cells at specific times. The research team used their experiments to study the incorporation of labeled nucleotides into a culture of lymphocytes and found that the lymphocytes incorporated the labeled nucleotide at a significantly higher level after a pathogen was introduced into the culture. They concluded that ________. a. infection causes lymphocyte cultures to skip some parts of the cell cycle b. the presence of the pathogen made the experiments too contaminated to trust the results c. infection causes cell cultures in general to reproduce more rapidly d. infection causes lymphocytes to divide more rapidly e. their tissue culture methods needed to be relearned

d. infection causes lymphocytes to divide more rapidly

Aggressive forms of breast cancer are resistant to Taxol chemotherapy. In these cancers, the gene encoding a protein called stathmin is overexpressed. To investigate the mechanism of action of stathmin, investigators measured tumor volume over time in mice with aggressive cancers under three conditions: no treatment (control), Taxol treatment, and Taxol treatment with stathmin gene expression turned off (Taxol + ΔΔstathmin). Their results are shown below. Use these results to hypothesize how the stathmin protein affects microtubule stability. a. The stathmin protein makes the cell membrane less permeable for the compounds like Taxol, therefore, Taxol couldn't reach a satisfactory concentration within the cell and doesn't affect significantly on microtubules' depolymerization. b. The stathmin protein enhances particular pathways of Taxol catabolism, so it is neutralized quite quickly in comparison to when the stathmin is absent. c. The stathmin protein binds to Taxol and inhibits its effect. d. The stathmin protein decreases the stability of microtubules. When stathmin is absent, the microtubule-stabilizing effect of Taxol is enhanced, and the cells are more likely to arrest.

d. the strathmin protein decreases the stability of microtubules. When stratmin is absent, the microtubule-stabilizing effect of taxol is enhanced, and the cells are more likely to arrest

As shown in this paper, the p53 protein (encoded by the p53 gene) plays a critical role at cell cycle checkpoints. Why is p53 sometimes called "the guardian of the genome"? Select all the statements that support p53 being called "the guardian of the genome." a. In response to DNA damage, active p53 proteins interrupt DNA replication during the S-phase of the cell cycle. b. Once activated, p53 proteins activate genes for DNA repair enzymes. c. After DNA damage, p53 proteins act as transcription factors to activate the p21 gene; the p21 protein inhibits the cell cycle. d. Given overwhelming DNA damage, p53 proteins induce apoptosis (programmed cell death). e. After DNA damage, p53 proteins are activated and arrest the cell cycle.

everything except a The p53 protein is a specific transcription factor that promotes the synthesis of cell cycle-inhibiting proteins, such as p21. The p21 protein halts the cell cycle by inhibiting the cyclin-cdk complex required for the transition from G1 to S phase. The p53 protein can also turn on genes directly involved in DNA repair mechanisms. When DNA is irreparable, the p53 proteins activate "cell suicide" genes whose protein products bring about apoptosis.

microtubules are actively ____ during the start of ____, when the mitotic spindle is produced. During ____, the kinectochore microtubules are ____ as daughter chromosomes move to opposite poles of the cell. At the end of ____, the spindle microtubules are ____ to remove the spindle before entering ___.

polymerized; m phase; anaphase; depolymerized; anaphase; depolymerized; G1 phase