LIFE 120 Chapter 9: The Cell Cycle
During what phase in the cell cycle would you find the most DNA per cell?
G2 Chromosomes are duplicated only during the S phase ("S" stands for synthesis of DNA) of interphase. The phase following completion of the S phase is G2 of interphase.
You would be unlikely to see which of the following human cells dividing?
nerve cell Nerve cells are quite complex and specialized. After reaching maturity, they enter the G0 phase.
In telophase of mitosis, the mitotic spindle breaks down and the chromatin uncoils. This is essentially the opposite of what happens in ________________.
prophase During prophase, we observe the formation of the spindle fibers, the condensation of chromatin, and the disappearance of the nucleolus.
In a human skin cell that is going through the cell cycle, when t=do he centrosomes separate?
prophase The centrosomes move away from each other during prophase, apparently propelled along the surface of the nucleus by the lengthening bundles of microtubules between them.
Following cytokinesis in an animal cell, how many centrioles does each new daughter cell possess?
two Each daughter cell inherits a single centrosome following cytokinesis and each centrosome contains two centrioles.
Assume that you are dealing with a species in which the number of chromosome in each somatic cell is 14. How many sister chromatids are present in the early telophase of mitosis?
0 In this case, mitosis starts with 14 chromosomes, each of which consists of two chromatids, because the cell has been through the S phase. By telophase, the chromatids have separated and the individual units of DNA (now called chromosomes) are arriving at the poles. There are no chromatids at this point.
A cell biologist carefully measured the quantity of DNA in grasshopper cells growing in cell culture. Cells examined during the G2 phase of the cell cycle contained 200 units of DNA. What would be the amount of DNA at G1 of the cell cycle in one of the grasshopper daughter cells?
100 units Recall that G2 follows S and that during the S phase of interphase in the cell cycle, DNA is replicated.
How many maternal chromosomes are present in a somatic (all body cells except reproductive cells) human cell not engaged in cell division)
23 Human somatic cells (all the body cells except the reproductive cells) contain a total of 46 chromosomes, half of which are maternally derived, and the other half paternally derived.
If a cell contains 60 chromatids at the start of mitosis, how many chromosomes will be found in each daughter cell at the completion of the cell cycle?
30 In this case, mitosis starts with 30 chromosomes, each of which consists of two chromatids. At the completion of mitosis, each daughter cell will contain 30 chromosomes.
If a normal somatic human cell is just about to divide, it has ____ chromatids.
92 Remember normal human cells have 46 chromosomes or 23 pairs. So human somatic cells will have 92 chromatids just prior to cell division due to the replication of DNA that occurs in S phase.
Down syndrome is characterized by cells having three copies of chromosome 21. As a cell in an individual with Down Syndrome prepares to enter mitosis, how many chromatids would be present?
94 Cells from and individual with Down syndrome would have 23 pairs of chromosomes, plus an extra chromosome at 21 for a total of 47. This is called trisomy because there is an extra chromosome at 21. At S phase, those chromosomes replicate to produce 94 sister chromatids.
What is the difference between a benign tumor and a malignant tumor?
Cells of benign tumors do not metastasize; those of malignant tumors do. Cells of malignant tumors spread from their site of origin to other parts of the body.
When a cell in S phase is fused with a cell in G1, __________________.
DNA synthesis begins immediately in the original G1 nucleus This observation indicates that cytoplasmic signals can participate in the regulation of the cell cycle.
The person credited with first recognizing (in the 1850s) that living cells cannot arise spontaneously, but arise only from previously existing cells, is ______________.
Rudolf Virchow
A cell entering the cell cycle with 32 chromosomes will produce two daughter cells, each with _____________.
There would be 32 chromosomes present in each of the daughter cells.
Which of the following processes DOES NOT occur in dividing bacteria? a. mitosis b. separation of the origins of replication c. replication of DNA d. binary fission e. inward growth of the plasma membrane
a. mitosis Mitosis does not occur in dividing bacteria. Mitosis might have had its origins in simpler bacterial mechanisms of cell reproduction. prokaryotes (bacteria) reproduce by a type of cell division called binary fission.
The function of he mitotic cell cycle is to produce daughter cells that ___________.
are genetically identical to the parent cell (assuming no mutation has occurred) Cell division involves the distribution of identical genetic material (DNA) to two daughter chromosomes.
A biochemist measured the amount of DNA in cells growing in the laboratory and found that the quantity of DNA in the cells doubled _______________.
between the G1 and G2 phases of interphase Between these two phases of the cell cycle, the DNA is replicated during the S phase.
The complex of DNA and protein that makes up a eukaryotic chromosome is properly called _________.
chromatin The DNA-protein complex called chromatin is organized into a long, thin fiber.
In animal cell mitosis, the cleavage furrow forms during which stage of the cell cycle?
cytokinesis of telophase Cytokinesis is usually well under way by telophase. In animal cells, cytokinesis involves the formation of a cleavage furrow, which pinches the cell in two.
During interphase, the genetic material of a typical eukaryotic cell is __________________.
dispersed in the nucleus as long stands of chromatin During interphase, the chromosomes cannot be distinguished individually because they are still in the form of loosely packed chromatin fibers.
Which of the following is involved int the binary fission of bacteria?
distribution of a copy of the single parental chromosome to each daughter cell Prokaryotes reproduce by a type of cell division called binary fission, which involves replicating the single chromosome and distributing the copies equally to two daughter cells.
Cytokinesis refers to ________________.
division of the cytoplasm Cytokinesis is the division of the cytoplasm that follows the mitotic division of the nucleus.
Observations of cancer cells in culture support the hypothesis that cancer cells __________________.
do not exhibit density-dependent inhibition Normal cells respond to density-dependent inhibition by growing in culture to form a single layer of cells.
Which of the following represents a mismatch or INCORRECT description? a. anaphase: there is movement of the chromosomes to the poles b. prophase: chromosomes become more tightly coiled c. metaphase: chromosomes line up on the equatorial plane d. telophase: chromosomes become more extended e. metaphase: the nuclear envelope disappears
e. metaphase: the nuclear envelope disappears During pro metaphase, the nuclear envelope fragments.
Tissue culture experiments with PDGF demonstrate that without this substance _______________________.
fibroblasts fail to divide PDGF is a specific growth factor for fibroblasts.
Chromatids are _______________________.
identical copies of each other if they are part of the same chromosome Each duplicated chromosome consists of two identical sister chromatids.
You would know a dividing cell was a plant cell rather than an animal cell if you saw that _______________.
it had formed a cell plate The cell plate, which divides the cytoplasm in two, forms during the telophase of mitosis in a plant cell.
At which stage of mitosis are chromosomes lined up in one place in preparation for their separation to opposite poles of the cell?
metaphase The chromosomes convene on the metaphase plate, an imaginary plane that is equidistant from the spindle's two poles.
Which of the following DOES NOT occur during mitosis?
replication of chromosomes The DNA of the chromosomes is replicated in the S phase of interphase before mitosis.
Which of the following phases of mitosis is essentially the opposite of pro metaphase in terms of the nuclear envelope?
telophase In pro metaphase, the nuclear envelope fragments and the kinetochores attach to microtubules. During telophase, fragments of the nuclear envelope begin to reassemble along with portions of the endomembrane system.
DNA replication occurs in ______________________.
the S phase of interphase in both somatic and reproductive cells
One event occurring during prophase is ____________.
the beginning of the formation of a spindle apparatus During prophase, the mitotic spindle begins to form.
During binary fission in a bacterium ____________________.
the origins of replication move apart This occurs during binary fission.