Chapter 12 Homework

Which of these phases encompasses all of the stages of mitosis but no other events?
A
B
C
E
D

E This is mitosis

During _____ both the contents of the nucleus and the cytoplasm are divided.
During _____ both the contents of the nucleus and the cytoplasm are divided.
S
G1
mitosis
G2
the mitotic phase

The mitotic phase The mitotic phase encompasses both mitosis and cytokinesis.

During _____ the cell grows and replicates both its organelles and its chromosomes.
During _____ the cell grows and replicates both its organelles and its chromosomes.
S
G1
mitosis
cytokinesis
interphase

Interphase These are the events of interphase.

In eukaryotic cells, chromosomes are composed of _____.
In eukaryotic cells, chromosomes are composed of _____.
DNA and RNA
DNA only
DNA and proteins
DNA and phospholipids

DNA and proteins

Nucleoli are present during _____.
Nucleoli are present during _____.
prophase
interphase
metaphase
anaphase
prometaphase

Interphase Nucleoli are present during interphase.

Cytokinesis often, but not always, accompanies _____.
Cytokinesis often, but not always, accompanies _____.
telophase
prometaphase
anaphase
metaphase
interphase

Telophase Cytokinesis often, but not always, accompanies telophase.

Chromosomes become visible during _____.
Chromosomes become visible during _____.
prophase
anaphase
metaphase
interphase
prometaphase

Prophase During prophase, the chromatin fibers become discrete chromosomes.

Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
Centromeres divide and sister chromatids become full-fledged chromosomes during _____.
telophase
anaphase
prometaphase
metaphase
interphase

Anaphase During anaphase, sister chromatids separate and daughter chromosomes migrate to opposite poles.

Spindle fibers attach to kinetochores during _____.
Spindle fibers attach to kinetochores during _____.
metaphase
telophase
interphase
prometaphase
anaphase

Prometaphase Attachment of spindle fibers to kinetochores is one of the events of prometaphase.

Anaphase

During anaphase centromeres come apart, and sister chromatids become full-fledged chromosomes, which migrate to opposite poles of the cell.

Cytokinesis as it occurs in animal cells

Cytokinesis in animal cells involves the formation of a cleavage furrow.

Prophase

Events of prophase include the condensation of chromatin and the dispersal of nucleoli.

Metaphase

During metaphase chromosomes align along the metaphase plate.

Prometaphase

The events of prometaphase include the attachment of spindle fibers to kinetochores.

Cytokinesis as it occurs in plant cells

Cytokinesis in plant cells involves the formation of a cell plate.

Telophase

During telophase both nuclear envelopes and nucleoli re-form.

Some cells have several nuclei per cell. How could such multinucleated cells be explained?
Some cells have several nuclei per cell. How could such multinucleated cells be explained?
The cell underwent repeated mitosis, but cytokinesis did not occur.
The cell underwent repeated cytokinesis but no mitosis.
The cell had multiple S phases before it entered mitosis.
The cell underwent repeated mitosis with simultaneous cytokinesis.

The cell underwent repeated mitosis, but cytokinesis did not occur.

During which phase of mitosis do the chromatids become chromosomes?
During which phase of mitosis do the chromatids become chromosomes?
prophase
anaphase
cytokinesis
metaphase
telophase

Anaphase

The first gap in the cell cycle (G1) corresponds to _____.
The first gap in the cell cycle (G1) corresponds to _____.
the phase between DNA replication and the M phase
the phase in which DNA is being replicated
the beginning of mitosis
normal growth and cell function

normal growth and cell function

A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. How many picograms would be found at the end of S and the end of G2?
A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. How many picograms would be found at the end of S and the end of G2?
8; 16
8; 8
12; 16
16; 8
16; 16

16; 16

A cell in late anaphase of mitosis will have _____.
A cell in late anaphase of mitosis will have _____.
one large nuclear envelope
no chromosomes in the center of the cell
chromosomes clustered tightly at the center
chromosomes clustered at one end of the cell
individual chromatids beginning to separate from one another

no chromosomes in the center of the cell

What happens if MPF (mitosis-promoting factor) is introduced into immature frog oocytes that are arrested in G2?
What happens if MPF (mitosis-promoting factor) is introduced into immature frog oocytes that are arrested in G2?
Nothing happens.
The cells enter mitosis.
The cells undergo meiosis.
Cell differentiation is triggered.

The cells enter mitosis.

The decline of MPF activity at the end of mitosis is due to _____.
The decline of MPF activity at the end of mitosis is due to _____.
the accumulation of cyclin
synthesis of DNA
the degradation of cyclin
decreased synthesis of Cdk
the destruction of the protein kinase Cdk

the degradation of cyclin

For the cell, why is it better to be held in G1 rather than S, G2, or M phase?
For the cell, why is it better to be held in rather than , , or phase?
G1 cells are the only ones that do not have their chromatin in a highly condensed state.
MPF is required to enter S phase, so the cell is committed to entering M phase if the cycle moves beyond G1.
G1 cells have not replicated their DNA in preparation for division.
G1 cells are larger and more likely to perform the normal functions of the cell.

G1 cells have not replicated their DNA in preparation for division.

What would happen if the kinase that adds the inhibitory phosphate to Cdk were defective?
What would happen if the kinase that adds the inhibitory phosphate to Cdk were defective?
MPF levels would become abnormally high.
M phase would begin prematurely.
The onset of M phase would be delayed.
Cdk concentrations would spike.

M phase would begin prematurely. Inhibitory phosphorylation of Cdk normally occurs in interphase, when cyclin levels are increasing, and inhibits the Cdk subunit of MPF from prematurely catalyzing the phosphorylation reactions that trigger M phase.

What role(s) do gap phases play in the cell cycle?
What role(s) do gap phases play in the cell cycle?
They allow chromosome replication to occur.
They allow chromosomes to condense prior to mitosis.
They allow cells to replicate organelles and manufacture additional cytoplasm.
They allow the nuclear envelope to re-form after mitosis.

They allow cells to replicate organelles and manufacture additional cytoplasm. G1 and G2 phases allow the cell to complete these steps so that daughter cells produced in M phase will be normal in size and function.