Molecular Biology - Chapter 12 Homework
Cytokinesis often, but not always, accompanies _____.
prometaphase anaphase interphase * telophase* metaphase
Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
prometaphase interphase metaphase telophase * anaphase*
Why do some species employ both mitosis and meiosis, whereas other species use only mitosis?
A single-celled organism only needs mitosis. They need only mitosis to make large numbers of cells such as sperm. * They need both if they are producing animal gametes.* They need meiosis if the cells are producing organs such as ovaries. They need only meiosis if they produce egg cells.
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.
After chromosome separation is complete, a network of microfilaments forms near the plane of cell division that will separate the two new 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.* The plasma membrane of the parent cell grows inward, eventually joining with the cell plate
Is the DNA condensed in all or part of this phase? G1 S G2 Beginning of M( Prophase -> early Anaphase) End of M (late Anaphase -> telophase)
No No No Yes Yes
Does the cell contain twice as much DNA in this phase as it did in the G1 phase? G1 S G2 Beginning of M( Prophase -> early Anaphase) End of M (late Anaphase -> telophase)
No Yes Yes Yes Yes
Are sister chromatids present in all or part of this phase: G1 S G2 Beginning of M( Prophase -> early Anaphase) End of M (late Anaphase -> telophase)
No Yes Yes Yes No
G1 Phase
Non-diving cells exit cell cycle
Cytochalasin B is a chemical that disrupts microfilament formation. How would this interfere with cell division?
formation of the cell plate binary fission formation of the mitotic spindle *cleavage* DNA replication
During _____ the cell grows and replicates both its organelles and its chromosomes.
mitosis cytokinesis * interphase* S G1
Metaphase
Kinetochores are motionless in relation to poles of cell
Cells will usually divide if they receive the proper signal at a checkpoint in which phase of the cell cycle? Cells will usually divide if they receive the proper signal at a checkpoint in which phase of the cell cycle?
* G1* M G2 cytokinesis S
G1 Checkpoint
At this point, cell commits to go through the cycle
Eukaryotes only
Before seperation, duplicated chromosomes condense. Nuclear envelope fragments, permitting chromosome separation. Two copies of the duplicated chromosomes are attached at their centromeres before separating.
M Checkpoint
Cell divides, forming two daughter cells
After chromosomes condense, the __________ is the region where the identical DNA molecules are most tightly attached to each other.
Centromere(s)
G2 Phase
Centrosome replicates
During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called ________.
Chromatin
Bacteria only
Chromsome separation begins at the origin of replication on DNA
Prophase
Cohesin join sister chromatids of duplicated chromosomes. Tubulins assumble into spindle microtubules
Anaphase
Cohesins break down. Kinetochores move toward poles of cell.
In most eukaryotes, division of the nucleus is followed by ____________; when the rest of the cell divides.
Cytokinesis
S Phase
DNA replication
During telophase, the nonkinetochore microtubules _________.
Disassemble
The presence of cell wall prevents the cell from dividing by constriction. Bacteria Animals Plants
False False True
During _____ both the contents of the nucleus and the cytoplasm are divided.
G2 *the mitotic phase* mitosis S G1
In dividing cells, most of the cell's growth occurs during _________.
Interphase
During mitosis, microtubules attach to chromosomes at the ________.
Kinetochore(s)
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
Prometaphase
Microtubules attack to kinetochores.
M Phase
Mitotic spindle begins to form
The _________________ is a cells structure consisting of microtubules, which forms during early mitosis and plays a role in cell division.
Mitotic spindle(s)
Both bacteria and eukaryotes
Replicated chromosomes seperate by attaching to some other structural feature of the cell. Chromosomes replicate before cell division.
DNA replication produces two identical DNA molecules, called __________, which separate during mitosis.
Sister chromatids
Telophase
Spindle microtubules disassemble.
Tubulin or tubulin-like molecules function in binary fission (in bacteria) or cytokinesis (in animals and plants). Bacteria Animals Plants
True False True
Cell divide by constriction of a ring of protein. Bacteria Animals Plants
True True False
During prohpase a homologous pair of chromosomes consists of _______>
Two chromosomes and four chromatids.
Diagram showing the motor protein of a kinetochore, whose function has been blocked due to the effect of an inhibitor. Will this cell elongate during mitosis? Will the sister chromatids separate from each other? Will the chromosomes move to the poles of the cells?
Yes Yes No
Spindle fibers attach to kinetochores during _____.
anaphase interphase telophase metaphase * prometaphase*
The ____________ are the organizing centers for microtubules involved in separating chromosomes during mitosis.
centrosome(s)
Chromosomes become visible during _____.
metaphase prometaphase interphase *prophase* anaphase
Nucleoli are present during _____.
metaphase * interphase* prometaphase prophase anaphase