CH 11

Studies of rapidly dividing embryonic animal cells revealed:

-that inhibition of protein synthesis blocks mitosis. -increased synthesis of certain proteins in sync with the cell cycle. -that increased levels of cyclin proteins are correlated with activation of cyclin-dependent kinase (CDK) enzymes. -a periodic activation of protein kinases in sync with the cell cycle.

A cell in prophase I of meiosis has _____ as many copies of chromosomes as each of the daughter cells following cytokinesis of meiosis II.

4 times

It is estimated that there are a total of 245 cells (roughly 50 trillion) in the adult human body. Starting from a fertilized egg, how many cell divisions would be required to produce 245, assuming that every cell divides in every cycle?

45 divisions

At the start of mitosis, how many sister chromatids are present in a human cell?

46

Why don't plant cells use a contractile ring to divide their daughter cells?

A contractile ring can't "pinch" a cell wall.

Which statement is true regarding binary fission?

DNA replication of the circular bacterial chromosome during binary fission is a bidirectional process, starting at one point but progressing in opposite directions.

Predict what would happen if crossing over between homologous chromosomes occurred as part of mitosis.

Daughter cells would not be genetically identical

A student was studying cell growth using cells grown in laboratory cultures. The cultures were synchronized so that all of the cells passed through the same stage of the cell cycle at the same time. The cells were examined during five different periods of time, intervals (A-E). The amount of DNA present per cell was determined for each interval. The graph shows the result of this study.

During S phase, cells replicate their chromosomes and double the amount of DNA per cell.

If you analyze the sequences of the two copies of any of the chromosomes shown in the karyotype, there would be slight sequence differences. What could account for the small differences between a few of the homologous chromosomes?

Each homologous chromosome in a pair is from a different parent

The most common form of hemophilia is a defect in blood clotting factor VIII, which is caused by a mutant form of a gene on the X chromosome. Boys who inherit that mutation from their mother suffer from uncontrolled bleeding. Girls carrying one copy of this mutation have near normal blood clotting. Uncommonly, a girl is born with hemophilia even though both parents have normal phenotypes. Which of the statements might explain hemophilia in a girl born to parents with normal blood clotting phenotypes?

Nondisjunction during sperm formation resulted in her receiving no sex chromosome from her father and an X chromosome from her mother; she is XO.

A woman has her genome sequenced and finds that she carries a mutation in p53. Will she develop cancer?

Possibly; this mutation is likely to predispose her to developing certain types of cancer.

A researcher is studying phases of the cell cycle in a population of cells during which there is an increase in the DNA content. This stage is most likely:

S phase

Suppose you analyze a time-lapse video of a cell under a microscope, and you observe what appears to be four chromatids tightly aligned along their lengths. Which of the answer choices is an interpretation of this observation?

The chromatids represent a bivalent and the cell is probably in Prophase I of meiosis.

A researcher is evaluating the expression of p53 in cells she is culturing in the laboratory. She notices that in a small group of cells, high levels of phosphorylated p53 occur in the nuclei. What can she deduce about these cells?

These cells likely contain damaged DNA.

Suppose you analyze a time-lapse video of a cell under a microscope and you observe what appears to be crosslike structures within a bivalent. Which of the answer choices is an interpretation of this observation?

These structures represent crossing over between non-sister chromatids.

Why are the X and Y chromosomes not considered homologous?

They do not carry the same set of genes.

How do CDKs promote cell division?

They phosphorylate proteins that allow passage through cell cycle checkpoints.

An example of second-division nondisjunction is when sister chromatids fail to separate during anaphase of meiotic cell division.

True

Evidence exists (especially in dinoflagellates) that mitosis evolved from binary fission. For example, in certain eukaryotic cells during mitosis, DNA is attached to the membrane of the nucleus (much like a circular chromosome of a bacterium is attached to the plasma membrane)

True

There are no discernible phenotypic effects for an individual with the genotype XYY.

True

A gene associated with promoting normal cell division is called:

a proto-oncogene

Which of the processes is most important for passage through the G1 cell cycle checkpoint?

activation of cyclin-dependent kinases

The process of cell division in a prokaryotic cell is called:

binary fission

What characteristics do you expect to observe with a microscope if you investigate the division of mitochondria and chloroplasts in eukaryotic cells?

circular DNA attached to the plasma membrane and binary fission

A malignant cancer differs from a benign tumor in that:

malignant cancers invade surrounding tissue and benign cancers do not.

The assembly of what cytoskeletal structures are initiated by the M cyclin-CDK complex?

microtubules

In which phase of mitosis do chromosomes condense?

prophase

In which phase of mitosis does the mitotic spindle form?

prophase

Reproduction by mitotic cell division:

results in two daughter cells that are genetically identical.

What process can account for the phenomenon wherein a normal XY male produces a sperm carrying two Y chromosomes?

second-division nondisjunction

Mitotic cell division is considered asexual because

the daughter cells receive DNA from one parent cell, and the daughter cells are genetically identical.

When do sister chromatids separate in meiosis?

Anaphase 2

In what way is cytokinesis in plant cells similar to binary fission in a bacterium?

Cell wall material is deposited to separate the daughter cells.

A cell that is not actively dividing is in what phase of the cell cycle?

G0

Meiosis _____ is sometimes called reductional division because _____.

I; the number of chromosomes is reduced by half

Meiosis _____ is similar to mitosis in that _____ separate.

II; sister chromatids

What is the role of the protein FtsZ in prokaryotes?

It forms a ring at the site of constriction.

What properties are associated with a malignant cancer?

It invades surrounding tissue. It is metastatic. It is fast growing.

Suppose you are observing some cells with a microscope, and you see a cell that appears to be dividing. You can see that as the cell starts to pinch in half, the DNA seems to be attached to the plasma membrane via a membrane protein. On further analysis, you find that this organism's DNA is circular - that is, it consists of a closed loop. What can you conclude about this organism and its mode of cell division?

It is a prokaryote that is dividing by binary fission

Why would a compound that interferes with bacterial cell wall synthesis be useful for treating a bacterial infection?

It would limit growth of the bacterial population through cell division.

At which stage of the cell cycle could you see sister chromatids with a microscope?

M

How must spindle microtubules attach to chromosomes during prometaphase of meiosis I?

Spindle microtubules from one pole must attach to both kinetochores in a pair of sister chromatids.

The prokaryotic protein FtsZ is evolutionarily related to eukaryotic tubulin. What does this mean?

The amino acid sequence for FtsZ is similar to tubulin. The overall protein structure of FtsZ is similar to tubulin. The two proteins evolved from a common ancestral protein. The gene sequence for FtsZ is similar to tubulin.

What would happen to the daughter cells if the G2 phase of the parent cell is shortened?

The cells would be smaller than normal.

There are laboratory techniques that allow researchers to determine the amount of DNA in cell nuclei. If you measure the amounts of DNA at the end of mitosis and at the end of meiosis, how do they compare to the starting cell (starting from prophase during mitosis and from prophase I during meiosis)?

The daughter cells at the end of mitosis have one-half the amount of DNA, and the daughter cells at the end of meiosis have one-fourth the amount of DNA.

What important difference is there between meiosis in males and females?

The division of cytoplasm differs between males and females

What would happen if a pair of sister chromatids only connected to the mitotic spindle at one of their kinetochores?

The sister chromatids would not separate. The chromosome would not line up properly at metaphase. One of the daughter cells would have an extra copy of that chromosome.

An early observation in the study of the development of sea urchin embryos was that there were several enzymes that became active and then inactive in synchrony with the pattern of rapidly repeating cell divisions. These enzymes had a common characteristic in that they phosphorylate (add phosphate groups to) other proteins. Furthermore, they are only active when bound to another protein—ones that vary in abundance at specific times during the cell cycle. These enzymes are:

cyclin dependent kinases

A zygote is:

diploid

In meiosis, recombination occurs:

during only prophase I and involves exchange between chromatids of homologous chromosomes.

A human cell with a total of 23 chromosomes is:

haploid

If a human has the genotype XXXY, they would:

have 2 inactivated X chromosomes and be male.

What is the function of histone proteins?

to package DNA in eukaryotic chromosomes

Phosphorylated p53 is a protein that accumulates in the nuclei of cells that have damaged DNA where it functions to block the cell cycle and activate DNA repair. The p53 gene that encodes this protein is an example of a(n):

tumor suppressor gene.