Biology-Exam 3
Which of the following occurs in binary fission but not in mitosis with cytokinesis?
duplicated chromosomes attach to the plasma membrane
Cytokinesis often, but not always, accompanies _____.
telophase
Which of the following statements best describes how cytokinesis differs between plant and animal cells?
Plant cells deposit vesicles containing cell wall building blocks on the metaphase plate; animal cells form a cleavage furrow.
What is the name of the microtubule-organizing center found in animal cells as an identifiable structure present during all phases of the cell cycle?
centrosome
Cytochalasin B is a chemical that disrupts microfilament formation. With which aspect of cell division would cytochalasin B interfere?
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
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.
(a) Vesicles from the Golgi apparatus move along microtubules, coalesce at the plane of cell division, and form a cell plate. (b) The cell plate consists of the plasma membrane and cell wall that will eventually separate the two daughter cells.
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.
(a)non-dividing cells exit cell cycle (b)at this point, cell commits to go through the cycle (c)DNA replicate (d)centrosome replicates (e)mitotic spindle begins to form (f)cell divides, forming two daughter cells
The division of a bacterial cell into two daughter cells (called binary fission) is accomplished by a protein called FtsZ. FtsZ is very similar to the tubulin subunits that form microtubules in eukaryotes. After the replicated bacterial chromosomes have moved to opposite ends of the cell, a ring of FtsZ proteins forms inside the plasma membrane in the region where the cell will divide. As the FtsZ ring constricts, the plasma membrane and bacterial cell wall fold in and eventually separate into two cells. 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.
-Cells divide by a constriction of a ring protein: True for bacteria True for animal False for plants -The presence of a cell wall prevents the cell from dividing by constriction: False for bacteria False for animals True for plant cells -Tubulin subunits or tubulin-like molecules function in the division of the cell: True for bacteria False for animals True for plants
The decline of MPF activity at the end of mitosis is due to
the degradation of cyclin.
Mitosis and cell cycle terminology 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.
1. DNA replication produces two identical DNA molecules, called sister chromatid(s), which separate during mitosis. 2. After chromosomes condense, the centromere(s) is the region where the identical DNA molecules are most tightly attached to each other. 3. During mitosis, microtubules attach to chromosomes at the kinetochore(s). 4. In dividing cells, most of the cell's growth occurs during interphase. 5. The mitotic spindle(s) is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division. 6. During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called chromatin. 7. In most eukaryotes, division of the nucleus is followed by cytokinesis, when the rest of the cell divides. 8. The centrosome(s) are the organizing centers for microtubules involved in separating chromosomes during mitosis.
A human bone marrow cell, in prophase of mitosis, contains 46 chromosomes. How many chromatids does it contain?
92
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.
Are sister chromatid present in all or part of this phase? G1-no S-yes G2-yes Beginning of M-yes End of M-no Is the DNA condensed in all or part of this phase?G1- no S-no G2-no Beginning of M-yes End of M-yes Does the cell contain twice as much DNA in this phase as it did in the G1 phase?G1- no S-yes G2-yes Beginning of M- yes End of M-yes
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.
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; two copies of the duplicated chromosome are attached at their centromeres before separating Both Bactria and eukaryotes: chromosomes replicate before cell division; replicated chromosomes separate by attaching to some other structural feature of the cell
How do cancer cells differ from normal cells?
Cancer cells may be immortal.
Eukaryotic chromatin is composed of which of the following macromolecules?
DNA and proteins
Which statement provides the best description of the interphase portion of the cell cycle?
During interphase, a cell is metabolically active.
Which of these phases encompasses all of the stages of mitosis but no other events?
E. This is mitosis
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.
Cells will usually divide if they receive the proper signal at a checkpoint in which phase of the cell cycle?
G1 phase
Which of the following correctly matches a phase of the cell cycle with its description?
G1, follows cell division
Cell A has half as much DNA as cells B, C, and D in a mitotically active tissue. Cell A is most likely in
G1.
Chromosomes become visible during _____.
prophase
The cell cycle control systems of cancer cells differ from those of normal cells.
Genetic changes alter the function of the cancer cell's protein products.
Which of the following statements describing kinetochores is correct?
They are sites at which microtubules attach to chromosomes.
What is true of all cancers?
They have escaped normal cell cycle controls.
Which of the following statements best describes a cleavage furrow?
a groove in the plasma membrane between daughter nuclei
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 statements describes a characteristic feature of metaphase?
alignment of chromosomes on the equator of the cell
Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
anaphase
In the cells of some organisms, mitosis occurs without cytokinesis. This will result in
cells with more than one nucleus.
One difference between cancer cells and normal cells is that cancer cells
continue to divide even when they are tightly packed together.
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.
During _____ the cell grows and replicates both its organelles and its chromosomes.
interphase
Nucleoli are present during _____.
interphase
Why is it difficult to observe individual chromosomes with a light microscope during interphase?
interphase chromosomes are long, thin strands unlike the condensed chromosomes visible in mitosis
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 cellular events occur in the G1 phase of the cell division cycle?
normal growth and cell function
Spindle fibers attach to kinetochores during _____.
prometaphase
Which of the following events would be most likely to produce cells with several nuclei?
repeated mitosis without cytokinesis
Which of the following occurs during S phase?
replication of the DNA
The mitotic spindle plays a critical role in which of the following processes?
separation of sister chromatids
FtsZ is a bacterial protein that forms a contractile ring involved in binary fission. Its function is analogous to which of the following structures in eukaryotic cells?
the cleavage furrow of eukaryotic animal cells
During _____ both the contents of the nucleus and the cytoplasm are divided.
the mitotic phase
Which of the following is true of benign tumors, but not malignant tumors?
they remain confined to their original site
