Download Raven/Johnson Biology 8e Chapter 10 - Answers 1.

Raven/Johnson Biology 8e
Chapter 10 - Answers
1. Which of the following is NOT involved in binary fission in prokaryotes?
a. Replication of DNA
b. Elongation of the cell
c. Separation of daughter cells by septum formation
d. Assembly of the nuclear envelope
The correct answer is d—
A. Answer a is incorrect. There must be two copies of the cell’s genetic material in order for
cell division to occur. Both daughter cells need their own copy of the parent cell’s DNA.
The correct answer is d—
B. Answer b is incorrect. Elongation is a necessary step to increase cell volume and
eventually divide into two new daughter cells.
The correct answer is d–—
C. Answer c is incorrect. Binary fission is not complete until the parent cell has divided into
two daughter cells. This process occurs through the formation of a septum in prokaryotic
cells.
The correct answer is d—Assembly of the nuclear envelope
D. Prokaryotic cells do not possess internal membranes. Their DNA exists within the
cytoplasm and is not contained in a nuclear envelope.
2. Chromatin is composed of—
a. RNA and protein
b. DNA and protein
c. sister chromatids
d. chromosomes
The correct answer is b—
A. Answer a is incorrect. Although RNA is associated with chromosomes, the term
chromatin refers to the material that physically makes up the chromosome, which is DNA
and protein.
The correct answer is b—DNA and protein
B. Answer b is correct. When DNA binds with histone proteins it forms chromatin.
The correct answer is b—
C. Answer c is incorrect. Sister chromatids are composed of chromatin, not the other way
around.
The correct answer is b—
D. Answer d is incorrect. Chromosomes are composed of chromatin.
3. What is a nucleosome?
a. It is a region in the cell’s nucleus that contains euchromatin.
b. It is a region of DNA wound around a collection of histone proteins.
c. It is a region of a chromosome made up of multiple loops of chromatin.
d. It is 30-nm fiber found in chromatin.
Raven/Johnson Biology 8e
Chapter 10 - Answers
The correct answer is b—
A. Answer a is incorrect. Euchromatin refers to regions of DNA that are actively expressed
(transcribed into RNA) in the cell’s nucleus.
The correct answer is b—It is a region of DNA wound around a collection of histone proteins.
B. Answer b is correct. The histones proteins function to coil the DNA and help package the
DNA within the nucleus.
The correct answer is b—
C. Answer c is incorrect. The multiple radial loops of a chromosome involve the 30-nm fiber
that already contains the nucleosome structures. They contribute to the larger overall
structure of the chromosome.
The correct answer is b—
D. Answer d is incorrect. The 30-nm fiber represents the larger folding of the nucleosomes
into solenoid coils.
4. How do sister chromatids differ from homologous chromosomes?
a. Sister chromatids only represent the maternal genetic contribution.
b. Homologous chromosomes are exact copies, but sister chromatids are just similar.
c. Homologous chromosomes are similar, but sister chromatids are exact copies.
d. Sister chromatids represent only half the genetic information stored in a
chromosome.
The correct answer c—
A. Answer a is incorrect. The term sister refers to the fact that these strands of DNA are
derived from the same “parent” strand of DNA.
The correct answer c—
B. Answer b is incorrect. The homologous chromosomes represent the maternal and paternal
contributions to an organism’s genome. They are not identical.
The correct answer c—Homologous chromosomes are similar, but sister chromatids are exact
copies.
C. Answer c is correct. The sister chromatids are formed when the DNA is replicated. They
are exact copies.
The correct answer c—
D. Answer d is incorrect. The sister chromatids are copies of the cell’s DNA. The two
chromatids are identical and contain all the information for any one chromosome.
5. What is the role of cohesin proteins in cell division?
a. They organize the DNA of the chromosomes into highly condensed structures.
b. They hold the DNA of the sister chromatids together.
c. They help the cell divide into two daughter cells.
d. They hold the microtubules onto the chromosome.
The correct answer is b—
Raven/Johnson Biology 8e
Chapter 10 - Answers
A. Answer a is incorrect. Condensin is the protein thought to be responsible for the
condensation of chromosomes.
The correct answer is b—They hold the DNA of the sister chromatids together.
B. Answer b is correct. The cohesin protein links the two sister chromatids together. Cohesin
is concentrated at the centromere in condensed chromosomes.
The correct answer is b—
C. Answer c is incorrect. The physical separation of the cell into two daughter cells is called
cytokinesis.
The correct answer is b—
D. Answer d is incorrect. The kinetochore is the structure responsible for linking
microtubules to sister chromatids.
6. Replication of the organelles of the eukaryotic cell occurs during—
a. interphase
b. G1
c. S
d. G2
The correct answer is d—
A. Answer a is incorrect. The term interphase refers to all phases of the cell cycle other than
mitosis. Organelle replication does occur during this time; however, there is a more
precise answer possible.
The correct answer is d—
B. Answer b is incorrect. Many cellular processes occur during G1; however, organelle
replication is not associated with this phase.
The correct answer is d—
C. Answer c is incorrect. S phase is associated with DNA replication.
The correct answer is d—G2
D. Answer d is correct. Organelles replicate during G2 in preparation for cell division.
7. Replicated copies of each chromosome are called_______ and are connected at the
_________.
a. homologues; centromere
b. sister chromatids; kinetochores
c. sister chromatids; centromere
d. homologues; kinetochore
The correct answer is c—
A. Answer a is incorrect. The DNA copies generated during S phase form the sister
chromatids. They are, however, held together by the centromere.
The correct answer is c—
Raven/Johnson Biology 8e
Chapter 10 - Answers
B. Answer b is incorrect. The DNA copies generated during S phase do form the sister
chromatids; however, the kinetochores function to link the chromatids to microtubules,
not to each other.
The correct answer is c—sister chromatids; centromere
C. Answer c is correct. S phase replicates the DNA to form the sister chromatids. The
chromatids are connected to each other by the centromere.
The correct answer is c—
D. Answer d is incorrect. The homologous chromosomes are separate strands of DNA and
not copies. Kinetochores link the chromatids to microtubules and not to each other.
8. Kinetochores are associated with which of the following on a sister chromatid?
a. Centromere
b. Centriole
c. Condensation
d. Cohesion
The correct answer is a—Centromere
A. Answer a is correct. The centromere is the point along the chromosome where the two
sister chromatids are connected and where the microtubules connect via the kinetochore.
The correct answer is a—
B. Answer b is incorrect. The centriole is a microtubule structure that organizes the mitotic
spindle. It is not part of the chromatids.
The correct answer is a—
C. Answer c is incorrect. Condensation is the packaging of the cell’s DNA into
chromosomes.
The correct answer is a—
D. Answer d is incorrect. Cohesion links the two sister chromatids, but is independent of the
presence of the kinetochores.
9. Separation of the sister chromatids and elongation of the cell occurs during—
a. prophase
b. prometaphase
c. anaphase
d. telophase
The correct answer is c—
A. Answer a is incorrect. The nuclear envelope breaks down, and the mitotic spindles form
during prophase. The sister chromatids are still connected.
The correct answer is c—
B. Answer b is incorrect. Prometaphase is a time when chromosomes are attaching to and
moving along the mitotic spindle. The sister chromatids are still connected.
The correct answer is c—anaphase
Raven/Johnson Biology 8e
Chapter 10 - Answers
C. Answer c is correct. The cohesin proteins holding the two chromatids together are severed
during anaphase. This allows the spindle microtubules to pull the two chromatids apart
while also causing the cell to elongate.
The correct answer is c—
D. Answer d is incorrect. The nuclear envelope reforms during telophase, and the mitotic
spindle disassembles. The separation of the sister chromatids and elongation of the cell
has already occurred.
10. Why is cytokinesis an important part of cell division?
a. It is responsible for the proper separation of genetic information.
b. It is responsible for the proper separation of the cytoplasmic contents.
c. It triggers the movement of a cell through the cell cycle.
d. It is responsible for the elongation of the cell.
The correct answer is b—
A. Answer a is incorrect. The proper separation of the genetic information in a cell depends
on the microtubule spindle.
The correct answer is b—It is responsible for the proper separation of the cytoplasmic contents.
B. Answer b is correct. Cytokinesis is the process that pinches the cell in two, distributing
the cytoplasm between the two daughter cells.
The correct answer is b—
C. Answer c is incorrect. The regulation of the cell cycle is controlled by proteins called
cyclins and the associated cyclin-dependent kinases.
The correct answer is b—
D. Answer d is incorrect. Elongation of the cell occurs independently of the process of
cytokinesis.
11. At which stage in the cell cycle does a cell make a commitment to undergo cell division?
a. At the G1/S checkpoint
b. At the G2/M checkpoint
c. At the spindle checkpoint
d. At cytokinesis
The correct answer is a—At the G1/S checkpoint
A. Answer a is correct. Once a cell has passed the G1 checkpoint and has replicated its DNA
(in S phase), it must undergo cell division to separate those DNA copies into daughter
cells.
The correct answer is a—
B. Answer b is not correct. The G2/M checkpoint is an important step that leads to mitosis;
however, the cell can only reach this step if it has already replicated its DNA.
The correct answer is a—
Raven/Johnson Biology 8e
Chapter 10 - Answers
C. Answer c is incorrect. The spindle checkpoint is an important step that ensures that the
sister chromatids are properly segregated into the daughter cells; however, the cell would
not reach this stage if it had not replicated its DNA.
The correct answer is a—
D. Answer d is incorrect. Cytokinesis is the physical separation of the two daughter cells;
however, a cell would not reach this stage without first committing to S phase.
12. How is the activity of cyclin-dependent kinases (Cdk’s) regulated?
a. Presence or absence of cyclins
b. Phosphorylation
c. Growth factors
d. All of the above
The correct answer is d—
A. Answer a is incorrect. Cdk activity requires the presence of cyclins; however, other
mechanisms regulate the activity.
The correct answer is d—
B. Answer b is incorrect. Phosphorylation is an important regulatory mechanism for Cdk, but
it is not the only one.
The correct answer is d—
C. Answer c is incorrect. Growth factors can influence the activity of Cdk by altering the
expression of cyclins; however, other mechanisms are involved in its regulation.
The correct answer is d—All of the above
D. Answer d is correct. All of the mechanisms listed above play a role in regulating Cdk.
13. Why is the function of the protein p53 important for preventing cancer?
a. It ensures that the chromosomes are properly aligned for anaphase.
b. It integrates signals in the cell leading to the production of cyclins.
c. It checks for DNA damage before allowing replication during S phase.
d. It functions as a phosphatase, removing phosphates to regulate Cdk.
The correct answer is c—
A. Answer a is incorrect. Alignment of the chromosomes at anaphase is important for the
proper segregation of sister chromatids to the two daughter cells. This process involves
the anaphase-promoting complex.
The correct answer is c—
B. Answer b is incorrect. Integration of cell signals is the job of proteins like Rb that interact
both with transcription factors and Cdk.
The correct answer is c—It checks for DNA damage before allowing replication during S phase.
C. Answer c is correct. The role of p53 protein is specific to G1. The activity of p53 prevents
the replication of damaged DNA that might lead to cancer.
Raven/Johnson Biology 8e
Chapter 10 - Answers
The correct answer is c—
D. Answer d is incorrect. Phosphatases (enzymes that remove phosphate groups) are
important in the regulation of the cell cycle; however, p53 is not a phosphatase.
14. What is a protooncogene?
a. A mutant gene associated with the cell cycle that lead to cancer
b. A normal gene that can result in cancer if it becomes mutated
c. A gene introduced into a cell that can cause cancer
d. A gene that suppresses unregulated cell divisions
The correct answer is b—
A. Answer a is incorrect. Mutant genes associated with cancer are called oncogenes.
The correct answer is b—A normal gene that can result in cancer if it becomes mutated
B. Answer b is correct. Protooncogenes are normal genes that have the potential to cause
cancer if they become mutated.
The correct answer is b—
C. Answer c is incorrect. A protooncogene is one that is normally present in the cell. It is not
introduced from an outside source.
The correct answer is b—
D. Answer d is incorrect. Genes that help to suppress uncontrolled cell division are called
tumor-suppressor genes.
Challenge Questions
1. Regulation of the cell cycle is very complex and involves multiple proteins, all interacting
to control the process of cell division. MPF is the cyclin-Cdk complex that is responsible
for moving the cell past the G2/M checkpoint. The activity of the cyclin-dependent kinase
of MPF is regulated by phosphorylation. Cdk is inhibited when it is phosphorylated by the
kinase, Wee-1. Predict what would happen to a cell if Wee-1 were absent.
Answer—If Wee-1 were absent then there would be no way for the cell to phosphorylate Cdk. If
Cdk is not phosphorylated, then it cannot be inhibited. If Cdk is not inhibited, then it will remain
active. If Cdk remains active, then it will continue to signal the cell to move through the G2/M
checkpoint, but now in an unregulated manner. The cells would undergo multiple rounds of cell
division without the growth associated with G2. As a consequence, the daughter cells will become
smaller and smaller with each division—hence the name of the protein!
2. Review your knowledge of signaling pathways (chapter 9). Create an outline illustrating
how a growth factor (ligand) can lead to the production of a cyclin protein that would
trigger S phase.
Answer—
Growth factor = ligand
1. Ligand binds to receptor (the growth factor will bind to a growth factor
receptor).
2. A signal is transduced (carried) into the cytoplasm.
Raven/Johnson Biology 8e
Chapter 10 - Answers
3. A signal cascade is triggered. Multiple intermediate proteins or second
messengers will be affected.
4. A transcription factor will be activated to bind to a specific site on the DNA.
5. Transcription occurs and the mRNA enters the cytoplasm.
6. The mRNA is translated and a protein is formed.
7. The protein functions within the cytoplasm—possibly triggering S phase.
If you study Figure 10.22 you will see a similar pathway for the formation of S phase proteins
following receptor–ligand binding by a growth factor. In this diagram various proteins in the
signaling pathway become phosphorylated and then dephosphorylated. Ultimately, the Rb protein
that regulated the transcription factor E2F becomes phosphorylated. This releases the E2F and
allows it to bind to the gene for S phase proteins and cyclins.