Mastering Biology- Chapter 12

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. This cell is most likely

a plant cell in the process of cytokinesis.

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of micro-tubules, 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.

In the cells of some organisms, mitosis occurs without cytoki-nesis. This will result in

cells with more than one nucleus.

Which of the following does not occur during mitosis?

replication of the DNA

What is true of all cancers?

They have escaped normal cell cycle controls.

How do cancer cells differ from normal cells?

Cancer cells may be immortal.

The cell cycle control systems of cancer cells differ from those of normal cells. Select the best explanation for this fact.

Genetic changes alter the function of the cancer cell’s protein products.

If a eukaryotic cell is in the G1 phase of the cell cycle, which statement 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.

An environmental substance that is known to cause cancer is called a what?

carcinogen

Radiation emitted from which of the following two sources are most alike?

microwaves and cellphones

You are trying to discover if the pesticide atrazine is a mutagen. Where are you looking for mutations?

DNA

Which of the following is true?

Cancer-causing substances work in many different ways.

Which of the following best summarizes current scientific opinion regarding cellphones and brain cancer?

While most studies indicate that cellphones do not cause brain cancer, more research needs to be done as cellphone use increases.

Which of the following codes for proteins?

genes

You are developing a new drug that damages the cells that provide the supportive structure required by a tumor. Which type of cell are you targeting?

fibroblast

A tumor would not be able to have its own blood supply if it weren’t for which of the following?

endothelial cells immune system cells

Which of the following appears to be true according to current research?

As the population of Helicobacter pylori decreases in the human body, cases of esophageal cancer increase.

Can you match these prefixes, suffixes, and word roots with their definitions?

single: haplo both, double: diplo- same: homo- (or homeo-) without, lack of, not: a- (or an-) small: micro- to produce: -gen- body: -some (or soma-) chromosomes: ploid color: chrom- self: auto- many: multi- end: telo- before: pro- two: bi- one: uni- between: inter- segment, body section: -mere thread: mito- cell: -cyte (or cyto-) moving: kin- (or kinet-)

Prior to this new technique, how were mice given cancerous tumors?

The tumors were implanted under the skin.

You are an oncologist. A patient presents with advanced prostate cancer and you follow standard protocol. What do you do?

The patient is treated with chemical castration.

You are an endocrinologist studying new treatments for prostate cancer. You have a patient with an unusually large level of dihydrotestosterone. Which of the following is true?

Your patient’s cancer has become resistant to the standard treatment.

Which of the following is true regarding prostate cancer cells?

They can activate and inactivate certain genes.

Your uncle has prostate cancer. Which of the following indicates improvement in his condition?

A decreasing PSA.

A particular cell has half as much DNA as some other cells in a mitotically active tissue. The cell in question is most likely in

G1

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the animal cell cycle would be most disrupted by cytochalasin B?

cleavage furrow formation and cytokinesis

Which of the following is a large reason behind the increase in breast cancer in developing countries?

Women are living longer.

Which of the following is true?

Worldwide, breast cancer is the most common cancer in women, and the largest cancer killer of women.

You are an oncologist specializing in colon cancer. A patient presents to you with disease that has spread to his bones and liver and there is no treatment available. What stage cancer is this?

4

A woman in Uganda is diagnosed with breast cancer. If any treatment is done, what is it most likely to be?

Only a mastectomy.

You are a breast cancer survivor and advocate in the U.S. Why do you promote self breast exams to women under 50 rather than annual mammograms?

Women under 50 tend to have denser breast tissue which often make mammograms inconclusive.

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

They need both if they are producing animal gametes.

A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes. How many chromatids does it contain?

92

Why is it difficult to observe individual chromosomes with a light microscope during interphase?

They have uncoiled to form long, thin strands.

In eukaryotic cells, chromosomes are composed of _____.

DNA and proteins

What is the final result of mitosis in a human?

genetically identical somatic cells containing 46 chromosomes

Starting with a fertilized egg (zygote), a series of five cell divisions would produce an early embryo with how many cells?

32

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

20

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.
Drag the terms on the left to correctly complete these sentences. Not all the terms will be used.

sister chromatid(s) centromere(s) kinetocchore(s) interphase mitotic spindle (s) chromatin cytokinesis centrosome (s)

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.
Drag each label to the appropriate target.

*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.

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 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.

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.
Drag each micrograph to the target that indicates the stage of mitosis or cytokinesis it shows.

*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.

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.

*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.

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 labels to the appropriate locations. Labels may be used once, more than once, or not at all.

lengthen lengthen; shorten disassemble

Consider three questions concerning the animal cell that has been treated with the inhibitor. Drag the labels to answer the questions. Labels may be used once, more than once, or not at all.

y y n

In all cells, separation of replicated chromosomes is a prerequisite for cell division. However, the mechanism of chromosome separation in bacteria is distinct from that in eukaryotes in several ways.
Sort the following statements into the appropriate bin.

*Although the processes of chromosome separation in bacteria and eukaryotes have a common evolutionary origin, the actual mechanisms are different. Structurally, bacterial cells contain a single chromosome that is much shorter than those in eukaryotic cells, and bacterial cells lack a mitotic spindle. The bacterial chromosome does not fully condense before separation. However, the physical separation of the replicated bacterial chromosomes still involves attachment to some structure in the cell: possibly the plasma membrane at the origins of replication.

Cytokinesis in animal cells is accomplished by constriction of the cell along the plane of cell division (formation of a cleavage furrow). In plant cells, which have cell walls, a completely different mechanism of cytokinesis has evolved.
Which of the following statements are true of cytokinesis in plant cells? Select the two that apply.

The cell plate consists of the plasma membrane and cell wall that will eventually separate the two daughter cells. Vesicles from the Golgi apparatus move along microtubules, coalesce at the plane of cell division, and form a cell plate.

Plant and animal cells also require cytoskeletal proteins for cytokinesis, although the roles these proteins play differ among bacteria, plants, and animals.
For each space in the table, drag the appropriate label to indicate if the statement is true or false for each group of organisms.

true; true; false false; false; true true; false; true

Which of these phases encompasses 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

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

Click on the art to see an animation. This animation illustrates the events of _____.

anaphase

Click on the art to see an animation. This animation illustrates the events of _____.

cytokinesis as it occurs in animal cells

Click on the art to see an animation. This animation illustrates the events of _____.

prophase

Click on the art to see an animation. This animation illustrates the events of _____.

metaphase

Click on the art to see an animation. This animation illustrates the events of _____.

prometaphase

Click on the art to see an animation. This animation illustrates the events of _____.

cytokinesis as it occurs in plant cells

Click on the art to see an animation. This animation illustrates the events of _____.

telophase

During prophase a homologous pair of chromosomes consists of _____.

two chromosomes and four chromatids

Which of the following is true of kinetochores?

They are sites at which microtubules attach to chromosomes.

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

G1: follows cell division

In some organisms, such as certain fungi and algae, cells undergo the cell cycle repeatedly without subsequently undergoing cytokinesis. What would result from this?

large cells containing many nuclei

Which of the following is found in binary fission but not in mitosis?

Duplicated chromosomes attach to the plasma membrane.

Cytochalasin B is a chemical that disrupts microfilament formation. How would this interfere with cell division?

cleavage

Scientists isolate cells in various phases of the cell cycle. They find a group of cells that have 1.5 times more DNA than G1 phase cells. The cells of this group are _____.

in the S phase of the cell cycle

The first gap in the cell cycle (G1) corresponds to _____.

normal growth and cell function

The microtubule-organizing center found in animal cells is an identifiable structure present during all phases of the cell cycle. Specifically, it is known as the _____.

centrosome

In human and many other eukaryotic species’ cells, the nuclear membrane has to disappear to permit _____.

the attachment of microtubules to kinetochores

The mitotic spindle is a microtubular structure that is involved in _____.

separation of sister chromatids

Metaphase is characterized by _____.

aligning of chromosomes on the equator

Kinetochore microtubules assist in the process of splitting centromeres by _____.

creating tension by pulling toward opposite poles

Some cells have several nuclei per cell. How could such multinucleated cells be explained?

The cell underwent repeated mitosis, but cytokinesis did not occur.

How is plant cell cytokinesis different from animal cell cytokinesis?

Plant cells deposit vesicles containing cell-wall building blocks on the metaphase plate; animal cells form a cleavage furrow.

FtsZ is a bacterial cytoskeletal protein that forms a contractile ring involved in bacterial cytokinesis. Its function is analogous to _____.

the cleavage furrow of eukaryotic animal cells

At which phase are centrioles beginning to move apart in animal cells?

prophase

If there are 20 centromeres in a cell at anaphase, how many chromosomes are there in each daughter cell following cytokinesis?

10

Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol disrupts microtubule formation. Surprisingly, this stops mitosis. Specifically, Taxol must affect _____.

the structure of the mitotic spindle

Which of the following are primarily responsible for cytokinesis in plant cells but not in animal cells?

Golgi-derived vesicles

Movement of the chromosomes during anaphase would be most affected by a drug that prevents _____.

shortening of microtubules

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?

G2

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

The beginning of anaphase is indicated by which of the following?

Cohesin is cleaved enzymatically.

During which phase of mitosis do the chromatids become chromosomes?

anaphase

A cleavage furrow is _____.

a groove in the plasma membrane between daughter nuclei

What is the correct chromosomal condition at prometaphase of mitosis?

B

What is the correct chromosomal condition for one daughter nucleus at telophase of mitosis?

E

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

formation of telophase nuclei

In the figure above, G1 is represented by which numbered part(s) of the cycle?

I or V

In the figure above, which number represents DNA synthesis?

II

In the figure above, at which of the numbered regions would you expect to find cells at metaphase?

III only

The data were obtained from a study of the length of time spent in each phase of the cell cycle by cells of three eukaryotic organisms designated beta, delta, and gamma.

Minutes Spent in Cell Cycle Phases

Of the following, the best conclusion concerning the difference between the S phases for beta and gamma is that

gamma contains more DNA than beta

Several organisms, primarily protists, have what are called intermediate mitotic organization.

These protists are intermediate in what sense?

They maintain a nuclear envelope during division.

What is the most probable hypothesis about these intermediate forms of cell division?

They show some but not all of the evolutionary steps toward complete mitosis.

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.

Which of the following question might be answered by using the method described?

What is the length of the S phase of the cell cycle?

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 _____.

infection causes lymphocytes to divide more rapidly

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. This cell is most likely _____.

a plant cell in the process of cytokinesis

Which of the following does NOT occur during mitosis?

replication of the DNA

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the cell cycle would be most disrupted by cytochalasin B?

cleavage furrow formation and cytokinesis

Motor proteins require which of the following to function in the movement of chromosomes toward the poles of the mitotic spindle?

ATP as an energy source

Which of these is NOT a carcinogen?

all of the above are carcinogens

_____ is a carcinogen that promotes colon cancer.

fat

Which of the following is a function of the S phase in the cell cycle?

The synthesis of sister chromatids

The copying of chromosomes occurs during which of the following phases of the cell cycle?

S phase

For the first several divisions of early frog embryos, cells proceed directly from the M phase to the S phase and back to M without gaps. Which of the following is likely to be true about dividing cells in early frog embryos?

The cells get smaller with each generation.

True or false? The M phase is characterized by the replication and division of a cell’s chromosomes.

F

If an organism normally has 34 chromosomes, how many molecules of DNA should there be in the G1 phase of the cell cycle?

34

Which of the following events would cause the cell cycle to arrest?

Poor nutrient conditions

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

G1

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

They remain confined to their original site

When cells were first taken from Henrietta Lacks, she was _____.

suffering from cervical cancer

How did doctors harvest and culture cells from Henrietta Lacks?

Cells were taken while she was being treated for cancer many years ago, and these cells have been cultured in the lab ever since.

Did doctors ask Henrietta Lacks’ permission to take her cells, and was she paid for them?

She was never told that her cells were being taken, and neither she nor her family has been compensated.

What property of Henrietta Lacks’ cells was most unusual when they were grown in the laboratory?

They continue to divide and multiply after decades of culture.

Cells taken from Henrietta Lacks have been used for experiments leading to _____.

tests of the effects of atomic radiation on life new treatments for cancer the development of a polio vaccine

What treatment is being compared to the control in the experiment?

The treated glioblastoma cells were cultured in the presence of an inhibitor from umbilical cord stem cells, but the control cells were cultured without the inhibitor.

The data are plotted in a type of graph called a histogram, which groups values for a numeric variable on the x-axis into intervals. A histogram allows you to see how an entire group of experimental subjects (cells, in this case) are distributed along a continuous variable (amount of fluorescence). In these histograms, the bars are so narrow that the data appear to follow a curve for which you can detect peaks and dips. Each bar represents the number of cells observed to have a fluorescence level in that interval. This in turn indicates the relative amount of DNA in those cells.
Which axis indirectly shows the relative amount of DNA per cell? By what relationship?

The x-axis; the DNA was stained, so there is a positive correlation between fluorescence and DNA content.

Which region shows the population of cells with the highest amount of DNA per cell?

region C

Identify which phase of the cell cycle is represented by each region. The regions represent the same cell cycle phases in both histograms.

region A: G1 region B: S region C: G2

In the control sample histogram, does the population of cells in the S phase show a distinct peak? Why or why not?

No; the DNA content per cell changes as the S phase progresses, so the cells in S phase have a range of fluorescence levels.

In the treated sample histogram, which phase of the cell cycle has the greatest number of cells?

the G1 phase

Which statement best describes the difference(s) in the distribution of cells in the treated sample compared to the control sample?

The treated cells are mostly in the G1 phase (region A), but in the control sample, there are peaks of cells in both G1 and G2 (region C).

What does the difference in distribution tell you about the cells in the treated sample?

The treated cancer cells are arrested at the G1 phase.

Which mechanism is the best explanation for how the stem cell-derived inhibitor might arrest the cancer cell cycle at the G1 stage?

The inhibitor might block the activity of a cyclin or signaling molecule of the G1 checkpoint.

The data were obtained from a study of the length of time spent in each phase of the cell cycle by cells of three eukaryotic organisms designated beta, delta, and gamma.

Minutes Spent in Cell Cycle Phases

The best conclusion concerning delta is that the cells _____.

are in the G0 phase.

Neurons and some other specialized cells divide infrequently because they _____.

have entered into G0

MPF is a dimer consisting of _____.

cyclin and a cyclin-dependent kinase

Cyclin-dependent kinase (Cdk) is _____.

an enzyme that attaches phosphate groups to other proteins

What happens if MPF (mitosis-promoting factor) is introduced into immature frog oocytes that are arrested in G2?

The cells enter mitosis.

Once a cell completes mitosis, molecular division triggers must be turned off. What happens to MPF during mitosis?

The cyclin component of MPF is degraded.

The M-phase checkpoint ensures that all chromosomes are attached to the mitotic spindle. If this does not happen, cells would most likely be arrested in _____.

metaphase

Which of the following is released by platelets in the vicinity of an injury?

PDGF

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?

cyclin

Which of the following triggers the cell’s passage past the G2 checkpoint into mitosis?

MPF

The cyclin component of MPF is destroyed toward the end of which phase?

M

In the figure above, MPF reaches its highest concentration during this stage.

III

Density-dependent inhibition is explained by which of the following?

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

Besides the ability of some cancer cells to overproliferate, what else could logically result in a tumor?

lack of appropriate cell death

Anchorage dependence of animal cells in vitro or in vivo depends on which of the following?

response of the cell cycle controls to signals from the plasma membrane

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?

The cells show characteristics of tumors.

For a chemotherapeutic drug to be useful for treating cancer cells, which of the following is most desirable?

It interferes with rapidly dividing cells.

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?

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

Exposure of zebrafish nuclei to meiotic cytosol resulted in phosphorylation of NEP55 and L68 proteins by cyclin-dependent kinase 2. NEP55 is a protein of the inner nuclear membrane, and L68 is a protein of the nuclear lamina. What is the most likely role of phosphorylation of these proteins in the process of mitosis?

They are involved in the disassembly of the nuclear envelope.

Density-dependent inhibition is a phenomenon in which crowded cells stop dividing at some optimal density and location. This phenomenon involves binding of a cell-surface protein to its counterpart on an adjoining cell’s surface. A growth inhibiting signal is sent to both cells, preventing them from dividing. Certain external physical factors can affect this inhibition mechanism.

Select the statement that makes a correct prediction about natural phenomena that could occur during the cell cycle to prevent cell growth.

As cells become more numerous, the amount of required growth factors and nutrients per cell becomes insufficient to allow for cell growth.

The person credited with first recognizing (in the 1860s) that living cells cannot arise spontaneously, but arise only from previously existing cells, is __________.

Rudolf Virchow

What is the difference between a benign tumor and a malignant tumor?

Cells of benign tumors do not metastasize; those of malignant tumors do.

The function of the mitotic cell cycle is to produce daughter cells that __________.

are genetically identical to the parent cell (assuming no mutation has occurred)

Which of the following hypotheses is best supported by observing cancer cells in a culture?()

The cancer cells do not exhibit density-dependent inhibition.

You would be UNLIKELY to see which of the following human cells dividing?

nerve cell

Can you match the terms associated with cancer to their descriptions?

benign tumor malignant tumor Metastasis cancer carcinoma

In sexually reproducing multicellular organisms, the main functions of mitosis are _____.

growth and development tissue repair/replacement of damaged cells

Which events occur during prophase?

The nuclear envelope breaks down. Chromosomes condense and are attached to spindle fibers.

Cytokinesis _____.

finishes mitosis by dividing the cytoplasm and organelles of the original parent cell into two separate daughter cells

During _____, the cell carries out its normal functions and the chromosomes are thinly spread out throughout the nucleus.

interphase

Looking through a light microscope at a dividing cell, you see two separate groups of chromosomes on opposite ends of the cell. New nuclear envelopes are taking shape around each group. The chromosomes then begin to disappear as they unwind. You are witnessing _____.

telophase

During binary fission in a bacterium, __________.

the origins of replication move apart

A biochemist measured the amount of DNA in cells growing in the laboratory and found that the quantity of DNA in the cells doubled __________.

between the G1 and G2 phases

What must happen before a cell can begin mitosis?

The chromosomes must be duplicated.

The centrosomes move away from each other and the nuclear envelope breaks up during which phase of mitosis?

Prophase

The chromosomes line up in the center of the cell during which phase of mitosis?

Metaphase

The sister chromatids separate and begin moving toward opposite poles of the cell during which phase of mitosis?

Anaphase

The chromosomes arrive at the poles and nuclear envelopes form during which phase of mitosis?

Telophase

At the end of the mitotic (M) phase, the cytoplasm divides in a process called _________________.

cytokinesis

Which of the following is FALSE regarding sister chromatids?

Both of the sister chromatids end up in the same daughter cell after cytokinesis has occurred.

The complex of DNA and protein that makes up a eukaryotic chromosome is properly called __________.

chromatin

Which of the following is involved in the binary fission of most bacteria?

distribution of a copy of the single parental chromosome to each daughter cell

The region of a chromosome in which the two double strands of replicated DNA are held together is called __________.

a centromere

Which of the following processes does NOT occur in dividing bacteria?

mitosis

The centromere is a region in which __________.

sister chromatids are attached to one another in prophase

A cell biologist carefully measured the quantity of DNA in grasshopper cells growing in cell culture. Cells examined during the G2 phase of the cell cycle contained 200 units of DNA. What would be the amount of DNA at G1 of the cell cycle in one of the grasshopper daughter cells?

100 units

How many maternal chromosomes are present in a somatic human cell not engaged in cell division?

23

Which of the following does NOT occur during mitosis?

replication of chromosomes

Tissue culture experiments with PDGF demonstrate that without this substance __________.

fibroblasts fail to divide

A cell entering the cell cycle with 32 chromosomes will produce two daughter cells, each with __________.

none of the listed numbers of chromosomes

Chromatids are __________.

identical copies of each other if they are part of the same duplicated chromosome

During interphase, the genetic material of a typical eukaryotic cell is __________.

dispersed in the nucleus as long strands of chromatin

In telophase of mitosis, the mitotic spindle breaks down and the chromatin uncoils. This is essentially the opposite of what happens in __________.

prophase

"Cytokinesis" refers to __________.

the division of the cytoplasm

If a cell contains 60 chromatids at the start of mitosis, how many chromosomes will be found in each daughter cell at the completion of the cell cycle?

30

DNA replication occurs in __________.

the S phase of interphase

Which of the following phases of mitosis is essentially the OPPOSITE of prometaphase in terms of the nuclear envelope?

telophase

In animal cell mitosis, the cleavage furrow forms during which stage of the cell cycle?

cytokinesis

If a human somatic cell is just about to divide, it has __________ chromatids.

92