Mastering Biology Chapter 9

Nucleoli are present during _____.

interphase

Cytokinesis often, but not always, accompanies _____.

telophase (Cytokinesis often, but not always, accompanies telophase.)

Chromosomes become visible during _____.

prophase (The chromatin fibers become discrete chromosomes.)

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

anaphase (During anaphase, sister chromatids separate and daughter chromosomes migrate to opposite poles.)

Spindle fibers attach to kinetochores during _____.

prometaphase (Attachment of spindle fibers to kinetochores is one of the events of pro metaphase.)

When the separate chromosomes are being pulled from one place to another? This animation illustrates the events of _____.

Anaphase

In animal cells ______ involves the formation of a cleavage furrow

Cytokinesis

Events of________ include the condensation of chromatin and the dispersal of nucleoli.

Prophase

During _______ chromosomes align along the metaphase plate.

Metaphase

The events of _________ include the attachment of spindle fibers to kinetochores.

Prometaphase

_____ in plant cells involves the formation of a cell plate.

Cytokinesis

During_______ both nuclear envelopes and nucleoli re-form.

Telophase

When a cleavage furrow appears and eventually pinch into 2 cells. This animation illustrates the events of _____.

cytokinesis as it occurs in animal cells

When the chromosomes become visible? This animation illustrates the events of _____.

Prophase

When chromosomes align laterally (along the metaphase plate: imaginary line located midway between the poles of the duplicated chromosomes and the original chromosomes), before they separate. This animation illustrates the events of _____.

Metaphase

When the chromosomes break the nuclear envelope, and attach to microtubules. This animation illustrates the events of _____.

prometaphase

When a cell plate divides into 2 cells. This animation illustrates the events of _____.

Cytokinesis as it occurs in Plant Cells

When the sister cells are completely divided through Cytokinesis. This animation illustrates the events of _____.

telophase

During prophase a homologous pair of chromosomes consists of _____.

two chromosomes and four chromatids

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

interphase

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

the mitotic phase (encompasses both mitosis and cytokinesis)

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

Mitosis

DNA replication produces two identical DNA molecules, called _____, which separate during mitosis.

sister chromatids

After chromosomes condense, the _____ is the region where the identical DNA molecules are most tightly attached to each other.

centromeres

During mitosis, microtubules attach to chromosomes at the ______.

kinetochores

In dividing cells, most of the cell’s growth occurs during ______.

interphase

The _____ is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division.

mitotic spindles

During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called _____.

chromatin

In most eukaryotes, division of the nucleus is followed by ______, when the rest of the cell divides.

cytokinesis

The _____ are the organizing centers for microtubules involved in separating chromosomes during mitosis.

centrosomes

The key structures involved in mitosis of an animal cell

The two SISTER CHROMATIDS of each duplicated chromosome beginning to attach to the MITOTIC SPINDLE by means of their KINETOCHORES. The CENTROSOMES anchor the MIT at opposite ends of the cell. CENTROMERE is the region of the chromosome where chromatids are most closely attached to each other.

Cell Cycle Phases: 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 the cycle. C. DNA replicates D. Centrosome replicates E. Mitotic spindle begins to form. F. Cell divides, forming two daughter cells.

Phases of the cell cycle

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.

Once a cell passes the ______ checkpoint, it usually completes the cell cycle–that is, it divides.

G1

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.

1. N Y Y Y N 2. N N N Y Y 3. N Y Y Y Y

Changes in DNA structure during the cell cycle:

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.

In ______ 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.

Prophase

In_____ 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.

Prometaphase

_________,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.

Metaphase

In ______ , the cohesin proteins are cleaved, and the kinetochores move toward the poles of the cell, separating the sister chromatids.

Anaphase

As _______ 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.

Telophase

What phase is this?

Cytokinesis

During prophase, the microtubules of the mitotic spindle ______.

lengthen

During anaphase, the nonkinetochore microtubules ______ and move past each other, and the kinetochore microtubules ______.

lengthen, shorten

During telophase, the non kinetochore microtubules ______.

disassemble

Roles of the mitotic spindle

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)

Comparing chromosome separation in bacteria and eukaryotes

bacteria only: *Chromosome separation begins at the origin of replication on DNA. Eukaryotes only: * Before separation, duplicated chromosomes condense. * Nuclear envelope fragments, permitting chromosome separation. * 2 copies of the duplicated chromosome are attached at their centromeres before separation. Both Bacteria and Eukariotes: * Chromosomes replicate before cell division. * Replicated chromosomes separate by attaching to some other structural feature of the cell.

Cytokinesis in plant cells

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

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

They have uncoiled to form long, thin strands.

Kinetochores

They are sites at which microtubules attach to chromosomes.

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

cleavage

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

Cells divide by constriction of a ring of proteins

bacteria: TRUE animals: TRUE plants: FALSE

The presence of a cell wall prevents the cell from dividing by constriction

bacteria: FALSE animals: FALSE plants: TRUE

Tubulin or tubulin-like molecules function in binary fission (in bacteria) or cytokinesis (in animals and plants).

bacteria: TRUE animals: FALSE plants: TRUE

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

G1

_____ is a carcinogen that promotes colon cancer.

Fat (A diet high in fat increases the risk of both colon and breast cancer.)

Carcinogens

cigarette smoke testosterone UV light Fat (All of these substances can cause cancer.)

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.

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.

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

How do cancer cells differ from normal cells?

Cancer cells may be immortal.