Question 1

You are leading a team of researchers at a pharmaceutical company.Your goal is to design drugs that help fight cancer.Specifically, you want to focus on drugs that bind to and inactivate certain proteins, thereby halting cell cycle progression.One of your team members suggests targeting the retinoblastoma (Rb) protein and inhibiting this protein.Will this approach be successful? Why or why not?

Accepted Answer

A) This approach will not be successful.Rb is tumor-suppressor protein, and functions to inhibit the action of a number of cell cycle regulatory proteins.A drug designed to inactivate the Rb protein would essentially create the same situation as in as a cell that lacks both copies of the Rb gene.Lack of Rb activity would release the inhibition of cell cycle regulatory proteins, thereby promoting cell cycle progression, rather than halting it. 
B) This approach will be successful.Rb is an oncogene, and functions to activate a number of cell cycle regulatory proteins.A drug designed to inactivate the Rb protein would halt the cell cycle in cells that contain an active Rb.As a result, cancer cells expressing a constitutively active Rb protein would be good targets for this type of therapeutic. 
C) This approach will be successful.Rb is tumor-suppressor protein, and functions to inhibit the action of a number of cell cycle regulatory proteins.A drug designed to inactivate the Rb protein would activate cell cycle inhibition.Lack of Rb activity would therefore inhibit the cell cycle regulatory proteins. 
D) This approach will not be successful.Rb is an oncogene, and functions to activate a number of cell cycle regulatory proteins.A drug designed to inactivate the Rb protein would actually activate cell cycle progression.As a result, this drug would likely make this situation worse for patients whose cancer cells contain mutant Rb.

Question 2

In G2, there are typically high levels of the mitotic cyclin.Why is cdc2 not active during G2 if the mitotic cyclin is present?

Accepted Answer

A) Cdc2 is also regulated by phosphorylation. 
B) Cdc2 does not bind to the mitotic cyclin. 
C) Cdc2 requires ubiquitination to be activated. 
D) Cdc2 also has to bind to cohesin to be activated.

Question 3

Following S phase, a human cell would have how many pairs of sister chromatids and individual DNA molecules?

Accepted Answer

A) 23 pairs of sister chromatids and 46 individual DNA molecules 
B) 23 pairs of sister chromatids and 92 individual DNA molecules 
C) 46 pairs of sister chromatids and 46 individual DNA molecules 
D) 46 pairs of sister chromatids and 92 individual DNA molecules

Question 4

You are examining the effect of maturation-promoting factor (MPF) in sea urchin cells, which have a diploid number of 36.If you fuse a dividing sea urchin cell with a G1 arrested oocyte, what would be the outcome?

Accepted Answer

A) The G1 cell would enter mitosis, but would likely arrest at the spindle checkpoint because the chromosomes have not been properly replicated. 
B) The G1 cell would undergo mitosis and its daughter cells would each have 36 chromosomes. 
C) The G1 cell would undergo mitosis and its daughter cells would each have 18 chromosomes. 
D) The G1 cell would first go through S phase and then mitosis.Its daughter cells would have 36 chromosomes.

Question 5

You are assembling a model of a chromosome, but begin having some trouble when you get to the step of forming chromatin loops.If you are unable to resolve this problem, what step of chromosome structure would you be unable to achieve?

Accepted Answer

A) Histone/DNA complex 
B) Nucleosome 
C) Solenoid 
D) Rosettes

Question 6

A somatic cell from a corn plant normally contains 20 chromosomes.How many sister chromatids would that cell contain during G2 of the cell cycle?

Accepted Answer

A) 0 
B) 10 
C) 20 
D) 40

Question 7

What time point represents G2?

Accepted Answer

A) 1 
B) 2 
C) 3 
D) 4

Question 8

In prophase, ribosomal RNA synthesis stops when the chromosomes condense, and as a result:

Accepted Answer

A) the chromosomes lengthen. 
B) the nuclear envelope reforms. 
C) the nucleolus disappears. 
D) the chromosomes line up at the equator of the cell.

Question 9

The division of a bacterial cell occurs as the:

Accepted Answer

A) cell wall develops cracks around the equator of the cell. 
B) chromosomes are pulled toward the ends of the cell. 
C) actin and microtubules constrict the cytoplasm. 
D) new membrane and cell wall materials begin to grow and form a septum.

Question 10

Embryonic cell cycles allow the rapid division of cells in the early embryo.These mitotic cell cycles are much shorter in length than the mitotic cell cycles of cells in a mature organism.In the embryonic cell cycles, mitosis takes approximately the same amount of time as it does in the cell cycles of mature cells.What do you think is a result of the embryonic cycle?

Accepted Answer

A) Resulting daughter cells are smaller than the mother cell in the embryonic cell cycles. 
B) Resulting daughter cells do not contain the same genetic information as the mother cell in the embryonic cell cycles. 
C) Resulting daughter cells cannot form a mitotic spindle in the embryonic cell cycle. 
D) Mother cells in the embryonic cell cycle spend the majority of their time in G0.

Question 11

The accommodation of the very long DNA strands that are part of a chromosome into the limited space of the nucleus is achieved by coiling the DNA around beads of histones into repeating subunits.These DNA-wrapped histones are called:

Accepted Answer

A) Solenoids 
B) Nucleosomes 
C) Chromatin loops 
D) Rosettes Review Figure 10.5

Question 12

This stage of the cell cycle is characterized by growth and it contains a checkpoint to verify that all of the DNA has been replicated prior to mitosis.

Accepted Answer

A) G1 
B) S 
C) G2 
D) Mitosis

Question 13

Before cell division of somatic cells, each chromosome must be replicated.After replication, the resulting two parts of each chromosome are held together by cohesin at the centromere.These two parts are referred to as:

Accepted Answer

A) Sister chromatids 
B) Homologous chromosomes 
C) Daughter chromosomes 
D) Kinetochores

Question 14

If there are 32 sister chromatids in a normal somatic cell, what is the haploid number for that cell?

Accepted Answer

A) 8 
B) 16 
C) 32 
D) 64

Question 15

The two copies of each type of chromosome found in normal somatic (body) cells in an organism, throughout the cell cycle, are called:

Accepted Answer

A) Sister chromatids 
B) Homologous chromosomes 
C) Daughter chromosomes 
D) Kinetochores

Question 16

If you were to think of the cell as a car, and mitosis as a process that drives that car to go, what would be a good analogy for a cell that has a mutation in both copies of a tumor-suppressor gene?

Accepted Answer

A) The gas pedal of a car gets stuck while pushed down. 
B) The gas pedal of a car does not work at all. 
C) The brake pedal of a car gets stuck while pushed down. 
D) The brake pedal of a car does not work at all. Tumor suppressor genes are like the brakes on the cell cycle.Normally, they prevent cell division in response to problems, such as damaged DNA or incomplete replication.If both copies of a tumor suppressor gene are mutated, that would mean that a cell could not stop dividing in response to normal signals.This is analogous to cutting the brakes on a car.No matter what "signals" emerge (a stop sign, a red light, etc.), it is not possible to stop the car using the brake because there is something wrong with the brakes.

Question 17

Interphase is made up of what stages of the cell cycle?

Accepted Answer

A) G1 + G2 + S 
B) S + cytokinesis 
C) prophase + metaphase + anaphase + telophase 
D) cytokinesis + mitosis

Question 18

A duplicate copy of all of the hereditary information contained in the nucleus of eukaryotic cells is made during what stage of the cell cycle?

Accepted Answer

A) G1 
B) S 
C) G2 
D) Mitosis

Question 19

During what stages of the cell cycle are sister chromatids bound together by cohesin?

Accepted Answer

A) G1, S, G2 
B) S, G2 
C) G1, S 
D) S, G2, prophase, metaphase

Question 20

You are conducting a genetic screen using Caenorhabditis elegans embryos to isolate mutations affecting anaphase (A).Therefore, you need to look for embryos in which

Accepted Answer

A) the centromeres do not move toward the poles. 
B) the poles do not move apart. 
C) the spindle apparatus does not disassemble. 
D) sister chromatids are mismatched and therefore fail to separate.

Exam 10: How Cells Divide

In G₂, there are typically high levels of the mitotic cyclin.Why is cdc2 not active during G₂ if the mitotic cyclin is present?