Biology Ch. 12 Mastering

True of false? The M phase is characterized by the replication and division of a cell's chromosomes

True -Correct: Cells replicate their chromosomes during the S phase and divide partition their chromosomes during the M phase

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

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

Spindle fibers attach to kinetochores during _____.

prometaphase -attachment of spindle fibers to kinetochores is one of the events of prometaphase

Cytokinesis often, but not always, accompanies _____.

telophase -Cytokinesis often, but not always accompanies telophase.

If an organism normally has 34 chromosomes, how many molecules of DNA should there be in the G1 phase of the cell cycle?

34 -There is one DNA molecule per chromosome

During which substage of mitosis do sister chromatids break apart and start moving to opposite poles of the cell?

Anaphase -Chromatids are pulled to opposite poles of the cell during anaphase, the fourth substage of mitosis

True of False? Mitosis takes place during M phase, which is the longest phase of the cell cycle.

False -Mitosis does indeed take place during M phase, but M phase is the shortest phase of the cell cycle.

To which part of the centromere do mitotic spindle fibers attatch during prometaphase?

Kinetochore -The kinetochore is the region of the centromere on the sister chromatid to which the mitotic spindle attaches.

During which stage of mitosis are chromosomes lined up in the center of the cell?

Metaphase -Chromosomes held by spindle fibers are lined up in the middle of the cell during metaphase, the third and middle stage of mitosis

Which of the following events would cause the cell cycle to arrest?

Poor nutrient conditions -Poor nutrient conditions would arrest the cell cycle at the G1 checkpoint.

Chromosomes become visible during _____.

Prophase -During prophase, the chromatin fibers become discrete chromosomes.

The copying of chromosomes occurs during which of the following phrases of the cell cycle?

S phase -Chromosomes must undergo replication before mitosis can occur; this copying occurs during the S phase

Which term describes two recently replicated DNA strands that are joined together just before cell division?

Sister chromatids -Sister chromatids are the two strands of a recently replicated chromosome that will be split apart during cell division.

Which stage of mitosis is characterized by the disintegration of mitotic spindles and the formation of two new nuclear membranes?

Telophase -the mitotic spindles disintegrate and a nuclear envelope begins to form around each set of chromosomes during telophase, the last substage of mitosis

For the first several divisions of early frog embryos, cells proceed directly from the M phase to the S phase and back to M without gaps. Which of the following is likely to be true about dividing cells in early frog embryos?

The cells get smaller with each generation. -Without gap phases, the cells have no opportunity to grow

Which event does not take place before the start of mitosis?

The nuclear envelope disintegrates -this event takes place during mitosis

Which of the following is a function of the S phase in the cell cycle?

The synthesis of sister chromatids -DNA replication occurs during S phase and results in two sister chromatids for each original chromosome

Which of these is NOT a carcinogen?

cigarette smoke, fat, UV light, testosterone, all of the above are carcinogens -all of these substances can cause cancer

___ is a carcinogen that promotes colon cancer

fat -a diet high in fat increases the risk of both colon and breast cancer

Nucleoli are present during _____.

interphase -Nucleoli are present during interphase

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

interphase -these are the events of interphase

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

the mitotic phase -the mitotic phase encompasses both mitosis and cytokinesis

During prophase a homologous pair of chromosomes consists of _____.

two chromosomes and four chromatids. -at this point each of the chromosomes consists of two chromatids.