Mastering Biology Chapter 12

How would the removal of growth factors affect asynchronous cultures of (1) normal human cells and (2) most human cancer cells?

(1) Arrest in G1; (2) no effect (Growth factors are responsible for allowing normal, but not most cancerous, cells to pass through the G1 checkpoint.)

Centromeres divide and sister chromatids become full-fledged chromosomes during _____.

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

What two types of defects does a cancerous cell possess?

Cancerous cells possess defects that make proteins required for cell growth active and tumor suppressor genes inactive.

What evidence suggests that during anaphase, kinetochore microtubules shorten at the kinetochore?

Daughter chromosomes were observed to move toward the pole FASTER than do the marked regions of fluorescently labeled kinetochore microtubules.

Which of these phases encompasses all of the stages of mitosis but no other events?

E

There are 12 chromosomes.

False

Which answer correctly identifies a cell-cycle checkpoint with a criterion for passing it?

G2 checkpoint: Chromosomes have replicated successfully.

What is the relationship among chromosomes, DNA, and genes?

Genes are encoded by DNA and found within chromosomes. (Chromosomes are composed of DNA and protein, and DNA is composed of genes and noncoding regions.)

Nucleoli are present during _____.

Interphase

What would happen if the kinase that adds the inhibitory phosphate to Cdk were defective?

M phase would begin prematurely.

What role(s) do gap phases play in the cell cycle?

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.)

Cytokinesis often, but not always, accompanies _____.

Telophase

For the experiment shown in Figure 12.6, which answer best describes what the prediction would be if chromosome movement were based on microtubule shortening at the spindle pole? See Section 12.2

The darkened section will move toward the spindle pole but the distance between chromosomes and the darkened section will remain constant. Daughter chromosomes will move toward the pole at the same rate as the darkened sections.

During _____ both the contents of the nucleus and the cytoplasm are divided.

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

What major events occur during anaphase of mitosis?

The sister chromatids of replicated chromosomes separate, and the spindle poles are pushed farther apart.

Aggressive forms of breast cancer are resistant to Taxol chemotherapy. In these cancers, the gene encoding a protein called stathmin is overexpressed. To investigate the mechanism of action of stathmin, investigators measured tumor volume over time in mice with aggressive cancers under three conditions: no treatment (control), Taxol treatment, and Taxol treatment with stathmin gene expression turned off (Taxol + Δstathmin). Their results are shown below. Use these results to hypothesize how the stathmin protein affects microtubule stability.

The stathmin protein decreases the stability of microtubules. When stathmin is absent, the microtubule-stabilizing effect of Taxol is enhanced, and the cells are more likely to arrest.

Each chromatid contains a single molecule of double-stranded DNA.

True

Each chromatid within a chromosome contains the same set of genes.

True

Each chromosome contains both DNA and protein.

True

There are 12 chromatids.

True

What could the investigators do to determine whether the regulatory molecule was present in the cytosol or in a cytoplasmic organelle?

Use differential centrifugation to separate the organelles and cytosol from M-phase cells and microinject only the organelles into the frog oocytes

Which of these is NOT a carcinogen?

all of the above are carcinogens

A strain of Staphylococcus aureus bacteria has become resistant to the powerful antibiotic methicillin, causing numerous lethal infections at a local hospital. The outbreak is a direct result of changes to the bacteria's __________.

alleles, genotype, and phenotype (One or more mutations caused a new allele to increase in frequency in the antibiotic-resistant population of bacteria, changing both its genotype and phenotype.)

_____ is a carcinogen that promotes colon cancer.

fat

During _____ the cell grows and replicates both its organelles and its chromosomes.

interphase

The defining characteristic of a malignant tumor is that _____.

its cells can spread to other parts of the body and produce secondary tumors

If a mutation has not occurred during DNA replication, how many different alleles of a gene would a replicated chromosome have?

one (The two chromatids of a replicated chromosome possess the same DNA sequences and thus the same alleles.)

How many different alleles of a certain gene could a normal diploid organism have?

one or two (A heterozygote organism can have up to two different alleles, but homozygotes have two copies of one allele.)

Spindle fibers attach to kinetochores during _____.

prometaphase

Chromosomes become visible during _____.

prophase (The chromatin fibers become discrete chromosomes.)

Identify the events in the cell cycle that must be completed successfully for daughter cells to share an identical complement of chromosomes.

the sister chromatids of each replicated chromosome must be partitioned in anaphase and fully separated into daughter cells by cytokinesis all the chromosomes must be replicated during the S phase the spindle apparatus must connect with the kinetochores of each sister chromatid in prometaphase

Part complete During prophase a homologous pair of chromosomes consists of _____.

two chromosomes and four chromatids

Chromosomes contain __________.

two types of macromolecules: nucleic acid and protein ( DNA is a nucleic acid that is packed around proteins within chromosomes.)