CHAPTER 12 AND 8.5

Why do some species employ both mitosis and meiosis, whereas other species use only mitosis?

Sexual reproduction requires both

During ___ both the contents of the nucleus and the cytoplasm are divided.

the mitotic phase

During __ the cell grows and replicates both its organelles and its chromosomes.

interphase

Which of the following correctly matches a phase of the cell cycle with its description?

G₁, follows cell division

Through a microscope, you can see a cell plate beginning to develop across the middle of a cell and nuclei forming on either side of the cell plate. The cell is most likely

a plant cell in the process of cytokinesis

Cells will usually divide if they receive the proper signal at a checkpoint in which of the cell cycle?

G₁

Which of the following is true of benign tumors, but not malignant tumors?

they remain confined to their original state

What is true of all cancers?

They have escaped normal cell cycle controls.

Eukaryotic chromatin is composed of which of the following macromolecules?

DNA and proteins

After DNA replication, each duplicated chromosome consists of two of which of the following structures?

sister chromatids

What is the name of the region on duplicated chromosomes where the sister chromatids are most closely attached to each other?

the centromere

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in

cells with more than one nucleus

The result of mitosis with cytokinesis is that the daughter cells end up with the same number of chromosomes that the parent cell had. Another potential way to maintain the number of chromosomes would be to carry out cell division first and then duplicate the chromosomes in each daughter cell. Do you think this would be an equally good way of organizing the cell cycle?

Neither daughter cell would contain all of the same genetic information found in the parent cell.

Students in a biology lab isolated cells in various phases of the cell cycle. A population of cells that have 1 ½ times the DNA of G₁ phase cells was most likely isolated from which of the following parts of the cell cycle?

in the S phase

Students in a biology lab isolated cells in various phases of the cell cycle. A population of cells that have twice the DNA of G₁ phase cells was most likely isolated from which of the following parts of the cell cycle?

in the G₂ phase

Which of the following cellular events occur in the G₁ phase of the cell division cycle?

normal growth and cell function

The mitotic spindle plays a critical role in which of the following processes?

separation of sister chromatids

Which of the following events would be most likely to produce cells with several nuclei?

repeated mitosis without cytokinesis

At which phase of the cell cycle do centroles begin to move apart in animal cells?

prophase

Movement of the chromosomes during anaphase would be most directly affected by a drug that prevents which of the following events?

shortening of microtubules

Which of the following events characterizes the beginning of anaphase?

enzymatic cleavage of cohesin

Which of the following statements best describes a cleavage furrow?

a groove in the plasma membrane between daughter nuclei

Which of the following events occurs during interphase of the cell cycle?

replication of the cell cycle

The drug cytochalasin B blocks the polymerization of actin microfilaments. Which of the following events of the cell cycle in animal cells would be most directly disrupted by cytochalasin B?

cleavage furrow formation and cytokinesis

Beginning with a fertilized egg (zygote), how many cells will be present in the embryo following six rounds of cell division?

64

In a diploid cell with three chromosome pairs (2n=6), how many centromeres are present in a nucleus at G₂ of the cell division cycle?

12

Which term below best describes the microtubule - organizing center found in animal cells as an identifiable structure present during all phases of the cell cycle?

centrosome

In a diploid cell with three chromosome pairs (2n=6), how many chromatids will be found in a nucleus at prophase of mitosis?

12

Which of the following statements best describes a characteristic feature of meta phase?

alignment of chromosomes on the equator of the cell

If there are 16 kinetochores in a cell at metaphase of mitosis, how many chromosomes will be found in each daughter cell following cytokinesis?

12

If a cell in G₁ of the cell cycle contains 12 chromosomes, how many sister chromatids will be present in a cell at prometaphase?

24

A population of cells is assayed for DNA content in G₁ of the cell cycle and is found to have an average of 8 picograms of DNA per nucleus. Approximately how many picograms of DNA would be found in a nucleus at metaphase of mitosis?

16

In which phase of the cell division cycle and mitosis are sister chromatids produced?

S

The unlettered circle at the top of the accompanying figure shows a diploid nucleus with four unreplicated chromosomes. The circles labeled Roman numerals I to V show various combinations of these chromosomes. Which chromosomal configuration would be observed at prometaphase of mitosis?

II

The unlettered circle at the top of the accompanying figure shows a diploid nucleus with four unreplicated chromosomes. The circles labeled Roman numerals I to V show various combinations of these chromosomes. Which chromosomal configuration would be observed in one daughter cell after telophase of mitosis?

V

If the cell whose nuclear material is shown in the accompanying figure continues toward completion of mitosis, which if the following events would occur next?

segregation of daughter chromosomes

One type of eukaryotic cell( line 1) spends 24 minutes in S phase and another type of cell (line 2) spends 48 minutes in S phase. Which of the following statements is the best explantion for the difference in time spent in S phase by lines 1 and 2?

Line 2 contains more DNA than line 1.

Nucleoli are present during ____.

interphase

Cytokinesis often, but not always, accompanies ____.

telophase

Chromosomes become visible during ___.

prophase

Centromeres divide and sister chromatids become full-fledged chromosomes during ___.

anaphase

Spindle fibers attach to kinetochores during ____.

prometaphase

Which of these phases includes all of the stages of mitosis but no other events?

E

During ____ both the contents of the nucleus and the cytoplasm are divided.

the mitotic phase

During__ the cell grows and replicates both its organelles and its chromosomes.

interphase

If a eukaryotic cell is in the G₁ phase of the cell cycle, which statements about the cell’s chromosomes must be correct?

Each chromosome is made of a complex of DNA and associated proteins.

Which statement provides the best description of the interphase portion of the cell cycle?

During interphase, a cell is metabolically active.

Through a microscope, you can see a cell plate beginning to develop across the middle of a cell and nuclei forming on either side of the cell plate. The cell is most likely

a plant cell in the process of cytokinesis

Which of the following occurs during S phase

replication of the DNA

Cell A has half as much DNA as cell B, C, and D in a mitotically active tissue. Cell A is most likely in

G₁

Which of the following statements best explains how neurons and some other specialized cells divide infrequently?

They have entered into G₀

Which of the following pairs of molecules make up an active MPF?

cyclin and a cyclin- dependent kinase

Which of the following statements best describes what would happen in MPF(mutation- promoting factor) is introduced into immune frog oocytes that are arrested in G₂?

The cells would enter mitosis.

If all chromosomes are not attached to the mitotic spindle at the M phase checkpoint, the cells would most likely be arrested at which of the following points in the cell division cycle of mitosis?

metaphase

Which of the following molecules is synthesized at specific times during the cell cycle and forms an active complex with a kinase?

cyclin

Which of the following molecules is maintained at a relatively constant level throughout the cell cycle but requires a cyclin to become catalytically active?

Cdk

Progression beyond the G₂ checkpoint into mitosis is triggered by which of the following molecules?

MPF

Besides the ability of some cancer cells to over proliferate, which of the following situations is most likely to result in a tumor?

lack of appropriate cell death

Which of the following statements best describes cells in culture that do not exhibit either density-dependent inhibition or anchorage dependence?

The cells show characteristics of tumors.

Which of the following characteristics would be most important for a chemotherapeutic drug designed to treat cancer cells?

It specifically inhibits the cell division cycle in rapidly dividing cells.

Cells from advanced malignant tumors often have very abnormal chromosomes and an abnormal number of chromosomes. Which of the following best explains the association between malignant tumors and chromosomal abnormalities?

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

Taxol is an anticancer drug extracted from the Pacific yew tree that prevents microtubule depolymerization. Which of the following processes would be least likely to occur in cells treated with taxol?

anaphase of mitosis

Which of the following statements best describes a property associated with a cyclin-dependent kinase (Cdk)?

A Cdk is an enzyme that attaches phosphate groups to other proteins.

At which stage of the cell cycle is the cyclin component of MPF degraded?

anaphase of mitosis

At what stage of the cell cycle is the concentration of the cyclin component of MPF at a minimum?

in mid-G₁

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to

disruption of mitotic spindle formation.

One difference between cancer cells and normal cells is that cancer cells

continue to divide even when they are tightly packed together.

The decline of MPF activity at the end of mitosis is due to

the degradation of cyclin.

Which of the following types of mutation would convert a proto-oncogene into an oncogene?

a mutation that greatly increases the amount of the proto-oncogene protein

Which of the following describes the role typical proto-oncogenes have when they are expressed in cells that are not cancerous?

They stimulate normal cell growth and division.

Which of the following statements correctly describes a characteristic of tumor-suppressor genes?

They encode proteins that help prevent uncontrolled cell growth.

Which of the following characterizes BRCA1 and BRCA2 as tumor-suppressor genes?

Their normal products participate in repair of DNA damage.

In colorectal cancer, several genes must be mutated for a cell to develop into a cancer cell. Which of the following kinds of genes would you expect to be mutated?

genes involved in controlling the cell cycle

Which of the following describes the normal function of the p53 gene product?

It inhibits the cell cycle so that damaged DNA is not replicated.

Tumors often have forms of the Ras protein that cause ________.

increased cell division

Which of the following would be most likely to lead to cancer?

Amplification of a proto-oncogene and inactivation of a tumor-suppressor gene

All your cells contain proto-oncogenes, which can change into cancer-causing genes. Why do cells possess such potential time bombs? (

Proto-oncogenes are necessary for the normal control of cell growth and division.

Proto-oncogenes can change into oncogenes that cause cancer. Which of the following best explains the presence of these potential time bombs in eukaryotic cells?

Proto-oncogenes normally help regulate cell division.