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