Mastering Biology Chapter 9
_____ in plant cells involves the formation of a cell plate.
Cytokinesis
When a cell plate divides into 2 cells. This animation illustrates the events of _____.
Cytokinesis as it occurs in Plant Cells
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.
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
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)
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.
In ______ , the cohesin proteins are cleaved, and the kinetochores move toward the poles of the cell, separating the sister chromatids.
Anaphase
When the separate chromosomes are being pulled from one place to another? This animation illustrates the events of _____.
Anaphase
How do cancer cells differ from normal cells?
Cancer cells may be immortal.
In animal cells ______ involves the formation of a cleavage furrow
Cytokinesis
What phase is this?
Cytokinesis
_____ is a carcinogen that promotes colon cancer.
Fat (A diet high in fat increases the risk of both colon and breast cancer.)
Cells will usually divide if they receive the proper signal at a checkpoint in which phase of the cell cycle?
G1
Once a cell passes the ______ checkpoint, it usually completes the cell cycle--that is, it divides.
G1
During _______ chromosomes align along the metaphase plate.
Metaphase
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
_________,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
Which of these phases encompasses all of the stages of mitosis but no other events?
Mitosis
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
The events of _________ include the attachment of spindle fibers to kinetochores.
Prometaphase
Events of________ include the condensation of chromatin and the dispersal of nucleoli.
Prophase
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
When the chromosomes become visible? This animation illustrates the events of _____.
Prophase
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.
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
During_______ both nuclear envelopes and nucleoli re-form.
Telophase
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.
Spindle fibers attach to kinetochores during _____.
prometaphase (Attachment of spindle fibers to kinetochores is one of the events of pro metaphase.)
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.
Kinetochores
They are sites at which microtubules attach to chromosomes.
Why is it difficult to observe individual chromosomes with a light microscope during interphase?
They have uncoiled to form long, thin strands.
Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
anaphase (During anaphase, sister chromatids separate and daughter chromosomes migrate to opposite poles.)
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.
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 divide by constriction of a ring of proteins
bacteria: TRUE animals: TRUE plants: FALSE
After chromosomes condense, the _____ is the region where the identical DNA molecules are most tightly attached to each other.
centromeres
The _____ are the organizing centers for microtubules involved in separating chromosomes during mitosis.
centrosomes
During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called _____.
chromatin
Carcinogens
cigarette smoke testosterone UV light Fat (All of these substances can cause cancer.)
Cytochalasin B is a chemical that disrupts microfilament formation. How would this interfere with cell division?
cleavage
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
One difference between cancer cells and normal cells is that cancer cells
continue to divide even when they are tightly packed together.
In most eukaryotes, division of the nucleus is followed by ______, when the rest of the cell divides.
cytokinesis
When a cleavage furrow appears and eventually pinch into 2 cells. This animation illustrates the events of _____.
cytokinesis as it occurs in animal cells
During telophase, the non kinetochore microtubules ______.
disassemble
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.
During _____ the cell grows and replicates both its organelles and its chromosomes.
interphase
In dividing cells, most of the cell's growth occurs during ______.
interphase
Nucleoli are present during _____.
interphase
During mitosis, microtubules attach to chromosomes at the ______.
kinetochores
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
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
The _____ is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division.
mitotic spindles
When the chromosomes break the nuclear envelope, and attach to microtubules. This animation illustrates the events of _____.
prometaphase
Chromosomes become visible during _____.
prophase (The chromatin fibers become discrete chromosomes.)
DNA replication produces two identical DNA molecules, called _____, which separate during mitosis.
sister chromatids
When the sister cells are completely divided through Cytokinesis. This animation illustrates the events of _____.
telophase
Cytokinesis often, but not always, accompanies _____.
telophase (Cytokinesis often, but not always, accompanies telophase.)
The decline of MPF activity at the end of mitosis is due to
the degradation of cyclin.
During _____ both the contents of the nucleus and the cytoplasm are divided.
the mitotic phase (encompasses both mitosis and cytokinesis)
During prophase a homologous pair of chromosomes consists of _____.
two chromosomes and four chromatids