Mastering Biology Assignment 5

A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. How many picograms would be found at the end of S and the end of G2?

16; 16

A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. Those cells would have __________ picograms at the end of the S phase and __________ picograms at the end of G2.

16; 16

If there are 20 duplicated chromosomes in a cell, how many centromeres are there?

20

A cell containing 92 chromatids at metaphase of mitosis would, at its completion, produce two nuclei each containing how many chromosomes?

46 The number of chromatids would be split in half with each nuclei.

Which term describes two recently replicated DNA strands that are joined together just before cell division? A) Sister chromatids B) Centriole C) Centrosome D) Centromere

A) Sister chromatids Sister chromatids are the two strands of a recently replicated chromosome that will be split apart during cell division.

Cyclin-dependent kinase (Cdk) is _____. A) an enzyme that attaches phosphate groups to other proteins B) the enzyme that catalyzes the attachment of chromosomes to microtubules C) inactive, or "turned off," in the presence of cyclin D) present only during the S phase of the cell cycle

A) an enzyme that attaches phosphate groups to other proteins

In some organisms, such as certain fungi and algae, cells undergo the cell cycle repeatedly without subsequently undergoing cytokinesis. What would result from this? A) large cells containing many nuclei B) inability to duplicate DNA C) division of the organism into many cells, most lacking nuclei D) a rapid rate of gamete production E) a decrease in chromosome number

A) large cells containing many nuclei

A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes. How many chromatids does it contain? A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes. How many chromatids does it contain? A) 23 B) 92 C) 23 or 46, depending on the portion of prophase examined D) 46 or 92, depending on the portion of prophase examined E) 46

B) 92 Mitosis follows the duplication of the cell's DNA.

Density-dependent inhibition is explained by which of the following? A) As cells become more numerous, they begin to squeeze against each other, restricting their size and ability to produce control factors. B) As cells become more numerous, the cell surface proteins of one cell contact the adjoining cells and they stop dividing. C) As cells become more numerous, the protein kinases they produce begin to compete with each other, such that the proteins produced by one cell essentially cancel those produced by its neighbor. D) As cells become more numerous, the level of waste products increases, eventually slowing down metabolism.

B) As cells become more numerous, the cell surface proteins of one cell contact the adjoining cells and they stop dividing.

Cells from advanced malignant tumors often have very abnormal chromosomes and an abnormal number of chromosomes. What might explain the association between malignant tumors and chromosomal abnormalities? A) Cancer cells are no longer anchorage-dependent. B) Cell cycle checkpoints are not in place to stop cells with chromosome abnormalities. C) Transformation introduces new chromosomes into cells. D) Cancer cells are no longer density-dependent.

B) Cell cycle checkpoints are not in place to stop cells with chromosome abnormalities.

Which event does not take place before the start of mitosis? A) Organelles proliferate. B) The nuclear envelope disintegrates. C) The parent cell grows. E) DNA is replicated.

B) The nuclear envelope disintegrates. This event takes place during mitosis.

Cytochalasin B is a chemical that disrupts microfilament formation. How would this interfere with cell division? A)formation of the mitotic spindle B) cleavage c) DNA replication D) formation of the cell plate E) binary fission

B) cleavage In animal cells, the cleavage furrow forms when a ring of microfilaments contracts, causing the parent cell to be pinched in two.

Which of the following is a protein synthesized at specific times during the cell cycle that associates with a kinase to form a catalytically active complex? A) PDGF B) cyclin C) Cdk D) MPF

B) cyclin

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to: A) inhibition of DNA synthesis. B) disruption of mitotic spindle formation. C) myosin denaturation and inhibition of cleavage furrow formation. D) suppression of cyclin production. E) inhibition of regulatory protein phosphorylation.

B) disruption of mitotic spindle formation.

Scientists isolate cells in various phases of the cell cycle. They find a group of cells that have times more DNA than G1 phase cells. The cells of this group are _____. A) between the G1 and S phases in the cell cycle B) in the S phase of the cell cycle C) in the M phase of the cell cycle D) in the G2 phase of the cell cycle

B) in the S phase of the cell cycle

Which is a general term for enzymes that activate or inactivate other proteins by phosphorylating them? A) PDGF B) protein kinase C) MPF D) cyclin E) Cdk

B) protein kinase

During which substage of mitosis do sister chromatids break apart and start moving to opposite poles of the cell? A) Metaphase B) Prophase C) Anaphase D) Telophase

C) Anaphase Chromatids are pulled to opposite poles of the cell during anaphase, the fourth substage of mitosis.

Which of the following correctly matches a phase of the cell cycle with its description? A) S: immediately precedes cell division B) M: duplication of DNA C) G1: follows cell division D) G2: cell division E) All of the above are correctly matched.

C) G1: follows cell division After mitosis and cytokinesis, the newly formed daughter cells enter the G1 phase.

For a chemotherapeutic drug to be useful for treating cancer cells, which of the following is most desirable? A) It is safe enough to limit all apoptosis. B) It does not alter metabolically active cells. C) It interferes with rapidly dividing cells. D) It interferes with cells entering G0.

C) It interferes with rapidly dividing cells.

During which stage of mitosis are chromosomes lined up in the center of the cell? A) Prophase B) Anaphase C) Metaphase D) Telophase

C) Metaphase Chromosomes held by spindle fibers are lined up in the middle of the cell during metaphase, the third and middle stage of mitosis.

A particular cyclin called cyclin E forms a complex with a cyclin-dependent kinase called Cdk 2. This complex is important for the progression of the cell from G1 into the S phase of the cell cycle. Which of the following statements is correct? A) The activity of the cyclin E/Cdk 2 complex is highest during G2. B) The amount of Cdk 2 is greatest during G1. C) The amount of cyclin E is highest during G1. D) The amount of Cdk 2 is greater during G1 compared to the S phase. E) The amount of cyclin E is greatest during the S phase.

C) The amount of cyclin E is highest during G1

During which phase of mitosis do the chromatids become chromosomes? A) telophase B) prophase C) anaphase D) metaphase

C) anaphase

Which term describes centromeres uncoupling, sister chromatids separating, and the two new chromosomes moving to opposite poles of the cell? A) prophase B) prometaphase C) anaphase D) telophase E) metaphase

C) anaphase

What is the final result of mitosis in a human? A) genetically identical gamete cells containing 46 chromosomes B) genetically identical somatic cells containing 23 chromosomes C) genetically identical somatic cells containing 46 chromosomes D) genetically different somatic cells containing 46 chromosome

C) genetically identical somatic cells containing 46 chromosomes

Neurons and some other specialized cells divide infrequently because they _____. A) show a drop in MPF concentration B) no longer have active nuclei C) have entered into G0 D) can no longer bind Cdk to cyclin

C) have entered into G0

Besides the ability of some cancer cells to over proliferate, what else could logically result in a tumor? A) inability of chromosomes to meet at the metaphase B) plate C) lack of appropriate cell death metastasis D) changes in the order of cell cycle stages E) inability to form spindles

C) lack of appropriate cell death

In human and many other eukaryotic species' cells, the nuclear membrane has to disappear to permit _____. A) the splitting of the centrosomes B) cytokinesis C) the attachment of microtubules to kinetochores D) he disassembly of the nucleolus

C) the attachment of microtubules to kinetochores

Which of the following is a protein maintained at steady levels throughout the cell cycle that requires cyclin to become catalytically active? A) cyclin B) MPF C) PDGF D) Cdk

D) Cdk

Measurements of the amount of DNA per nucleus were taken on a large number of cells from a growing fungus. The measured DNA levels ranged from 3 to 6 picograms per nucleus. In which stage of the cell cycle did the nucleus contain 6 picograms of DNA? A) G1 B) S C) M D) G2

D) G2

To which part of the centromere do mitotic spindle fibers attach during prometaphase? A) Centriole B) Chromosome C) Microtubule D) Kinetochore

D) Kinetochore The kinetochore is the region of the centromere on the sister chromatid to which the mitotic spindle attaches.

A research team began a study of a cultured cell line. Their preliminary observations showed them that the cell line did not exhibit either density-dependent inhibition or anchorage dependence. What could they conclude right away? A) The cells are unable to form spindle microtubules. B) They were originally derived from an elderly organism. C) They have altered the series of cell cycle phases. D) The cells show characteristics of tumors.

D) The cells show characteristics of tumors.

Why is it difficult to observe individual chromosomes with a light microscope during interphase? A) The spindle must move them to the metaphase plate before they become visible. B) The DNA has not been replicated yet. C) They leave the nucleus and are dispersed to other parts of the cell. D) They have uncoiled to form long, thin strands. E) Sister chromatids do not pair up until division starts.

D) They have uncoiled to form long, thin strands. Except during the M phase, the DNA is extended, allowing its genes to be transcribed for protein synthesis.

Which of the following is true of benign tumors, but not malignant tumors? A) They are the result of the transformation of normal cells. B) They migrate from the initial site of transformation to other organs or tissues. C) They have an unusual number of chromosomes. D) They remain confined to their original site E) They can divide indefinitely if an adequate supply of nutrients is available.

D) They remain confined to their original site Benign tumors can often be surgically removed because their boundaries are well defined, whereas some malignant tumors go on to metastasize.

At which phase are centrioles beginning to move apart in animal cells? A) metaphase B) prometaphase C) anaphase D) prophase

D) prophase

Which of the following is a protein maintained at constant levels throughout the cell cycle that requires cyclin to become catalytically active? A) PDGF B) cyclin C) MPF D) protein kinase E) Cdk

E) Cdk

Which of the following is true of kinetochores? A) They are located at the center of the centrosome; their function is to organize tubulin into elongated bundles called spindle fibers. B) They attach to the ring of actin along the cytoplasmic surface of the plasma membrane, causing the actin to contract to form the cleavage furrow. C) They interdigitate at the cell's equator and then move apart, causing the cell to elongate. D) They are the primary centromere structures that maintain the attachment of the sister chromatids prior to mitosis. E) They are sites at which microtubules attach to chromosomes.

E) They are sites at which microtubules attach to chromosomes. As the spindle depolymerizes, the kinetochores appear to move along the spindle fiber, dragging the attached chromosomes with them.

True or false? Mitosis takes place during M phase, which is the longest phase of the cell cycle.

False Mitosis does indeed take place during M phase, but M phase is the shortest phase of the cell cycle.

Cells that are in a nondividing state are in which phase?

G0