Chapter 12 Mastering Biology

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

mitotic spindle(s)

Which of the following does NOT occur during mitosis?

replication of DNA

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

sister chromatid(s)

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

chromatin

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

cleavage

Eukaryotes ONLY

- Before separation, duplicated chromosomes condense. - Nuclear envelope fragments, permitting chromosomes separation. - Two copies of the duplicated chromosome are attached at their centromeres before separating.

Both Bacteria and Eukaryotes

- Chromosomes replicate before cell division. - Replicated chromosomes separate by attaching to some other structural feature of the cell.

Anaphase

- Cohesins break down. - Kinetochores move toward poles of the cell - The cohesin proteins are cleaved, and the kinetochores move toward the poles of the cell, separating the sister chromatids.

Metaphase

- Kinetochores are motionless in relation to poles of cell. - 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.

Prometaphase

- Microtubules attach to kinetochores. - 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.

Telophase

- Spindle microtubules disassemble. - 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.

Prophase

- Tubulins assemble into spindle microtubules. - Cohesins join sister chromatids of duplicated chromosomes. - 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.

Which of the following statements are true of 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.

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

20

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 construction of a ring of protein.

Bacteria: True Animals: True Plants: False

Bacteria ONLY

Chromosomes separation begins at the origin of replication on DNA.

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

G1

Is the DNA condensed in all or part of this phase?

G1: No S: No G2: No Beginning of M (prophase-anaphase): Yes End of M (anaphase-telophase): Yes

Are sister chromatids present in all or part of this phase?

G1: No S: Yes G2: No Beginning of M (prophase-anaphase): Yes End of M (anaphase-telophase): No

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 (prophase-anaphase): Yes End of M (anaphase-telophase): Yes

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

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

They need both if they are producing animal gametes. The form of cell division that produces animal gametes is meiosis, not mitosis. The production of gametes in plants is a function of both mitosis and meiosis

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

centromere(s)

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

centrosome(s)

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

cytokinesis

During telophase, the nonkinetochore microtubules ________

disassemble

In dividing cells, most of the cell's growth occurs during ________.

interphase

During mitosis, microtubules attach to chromosomes at the ________.

kinetochore(s)