8.E: Cell Division by Mitosis (Exercises)
8.1: Cell Division
Multiple Choice
A diploid cell has ________ the number of chromosomes as a haploid cell.
A. one-fourth
B. one-half
C. twice
D. four times
- Answer
-
C
An organism’s traits are determined by the specific combination of inherited ________.
A. cells
B. genes
C. proteins
D. chromatids
- Answer
-
B
The first level of DNA organization in a eukaryotic cell is maintained by which molecule?
A. cohesin
B. condensin
C. heterochromatin
D. histone
- Answer
-
D
Identical copies of chromatin held together by cohesin at the centromere are called _____.
A. histones
B. nucleosomes
C. chromatin
D. sister chromatids
- Answer
-
D
Free Response
Compare and contrast a human somatic cell to a human gamete.
- Answer
-
Human somatic cells have 46 chromosomes, including 22 homologous pairs and one pair of nonhomologous sex chromosomes. This is the 2 n, or diploid, condition. Human gametes have 23 chromosomes, one each of 23 unique chromosomes. This is the n, or haploid, condition.
Eukaryotic chromosomes are thousands of times longer than a typical cell. Explain how chromosomes can fit inside a eukaryotic nucleus.
- Answer
-
The long eukaryotic chromosomes can fit into the nucleous of a cell due to the compaction of DNA packaging. The double stranded DNA is wrapped around histones to form nucleosomes and then folded on itself to form compact 30-nm chromatin fibers. These chromatin are then further compacted into loop domains to creat heterochromatin.
8.2: The Cell Cycle
Multiple Choice
Chromosomes are duplicated during what portion of the cell cycle?
A. G
1
phase
B. S phase
C. prophase
D. prometaphase
- Answer
-
B
Separation of the sister chromatids is a characteristic of which stage of mitosis?
A. prometaphase
B. metaphase
C. anaphase
D. telophase
- Answer
-
C
The individual chromosomes become visible with a light microscope during which stage of mitosis?
A. prophase
B. prometaphase
C. metaphase
D. anaphase
- Answer
-
A
The mitotic spindles arise from which cell structure?
A. centromere
B. centrosome
C. kinetochore
D. cleavage furrow
- Answer
-
B
Unpacking of chromosomes and the formation of a new nuclear envelope is a characteristic of which stage of mitosis?
A. prophase
B. metaphase
C. anaphase
D. telophase
- Answer
-
D
Free Response
Describe the similarities and differences between the cytokinesis mechanisms found in animal cells versus those in plant cells.
- Answer
-
There are very few similarities between animal cell and plant cell cytokinesis. In animal cells, a ring of actin fibers is formed around the periphery of the cell at the former metaphase plate. The actin ring contracts inward, pulling the plasma membrane toward the center of the cell until the cell is pinched in two. In plant cells, a new cell wall must be formed between the daughter cells. Because of the rigid cell walls of the parent cell, contraction of the middle of the cell is not possible. Instead, a cell plate is formed in the center of the cell at the former metaphase plate. The cell plate is formed from Golgi vesicles that contain enzymes, proteins, and glucose. The vesicles fuse and the enzymes build a new cell wall from the proteins and glucose. The cell plate grows toward, and eventually fuses with, the cell wall of the parent cell.
Chemotherapy drugs such as vincristine (derived from Madagascar periwinkle plants) and colchicine (derived from autumn crocus plants) disrupt mitosis by binding to tubulin (the subunit of microtubules) and interfering with microtubule assembly and disassembly. Exactly what mitotic structure is targeted by these drugs and what effect would that have on cell division?
- Answer
-
These drugs will target the mitotic spindle, a structure made of microtubules, responsible for the proper separation of chromosomes during cell division. By interfering with the function of the mitotic spindle, these drugs will result in a failure of the spindle fibers to reach/attach to the chromosomes leading to poor chromosome alignment at the metaphase plate and errors in sister chromatid separation in anaphase.
8.3: Control of the Cell Cycle
Multiple Choice
What is necessary for a cell to pass the G 2 checkpoint?
A. cell has reached a sufficient size
B. an adequate stockpile of nucleotides
C. accurate and complete DNA replication
D. proper attachment of mitotic spindle fibers to kinetochores
- Answer
-
C
At which of the cell-cycle checkpoints do external forces have the greatest influence?
A. G
1
checkpoint
B. G2 checkpoint
C. M checkpoint
D. G
0
checkpoint
- Answer
-
A
If the M checkpoint is not cleared, what stage of mitosis will be blocked?
A. prophase
B. prometaphase
C. metaphase
D. anaphase
- Answer
-
D
Free Response
Describe the general conditions that must be met at each of the three main cell-cycle checkpoints.
- Answer
-
The three main cell-cycle checkpoints ensure proper progression and prevent errors. The general conditions that must be met at each are described below.
- G1 Checkpoint: Ensures the cell has adequate size, sufficient nutrients, and undamaged DNA before entering S phase.
- G2 Checkpoint: Confirms that DNA replication is complete, DNA is intact, and the cell is large enough to enter mitosis.
- M Checkpoint: Verifies that all chromosomes are correctly attached to spindle fibers and aligned before allowing separation in anaphase.
Rb is a negative regulator that blocks the cell cycle at the G 1 checkpoint until the cell achieves a requisite size. What molecular mechanism does Rb employ to halt the cell cycle?
- Answer
-
Rb halts the cell cycle at the G1 checkpoint by regulating the activity of E2F transcription factors, which are essential for the progression from G1 to S phase. Unphosphorylated Rb is active and binds E2F, preventing the expression of genes necessary for the G1/S phase transition. Once the requisite cell size has been reached Rb will be be phosphorylated, causing it to release E2F, lifting the "break" on cell cycle progression.
8.4: Cancer and the Cell Cycle
Multiple Choice
________ are changes to the nucleotides in a segment of DNA that codes for a protein.
A. Proto-oncogenes
B. Tumor suppressor genes
C. Gene mutations
D. Negative regulators
- Answer
-
C
A gene that codes for a positive cell cycle regulator is called a(n) ________.
A. kinase inhibitor
B. tumor suppressor gene
C. proto-oncogene
D. oncogene
- Answer
-
C
Which molecule is a Cdk inhibitor that is controlled by p53?
A. cyclin
B. anti-kinase
C. Rb
D. p21
- Answer
-
D
Free Response
Outline the steps that lead to a cell becoming cancerous.
- Answer
-
If one of the genes that produce regulator proteins becomes mutated, it produces a malformed, possibly non-functional, cell-cycle regulator. This increases the chance that more mutations will be left unrepaired in the cell. Each subsequent generation of cells sustains more damage. The cell cycle can speed up as a result of loss of functional checkpoint proteins. The cells can lose the ability to self-destruct.
Explain the difference between a proto-oncogene and a tumor suppressor gene.
- Answer
-
A proto-oncogene is the segment of DNA that codes for one of the positive cell-cycle regulators. If that gene becomes mutated to a form that is overactive, it is considered an oncogene. A tumor suppressor gene is a segment of DNA that codes for one of the negative cell-cycle regulators. If that gene becomes mutated to a form that is underactive, the cell cycle will run unchecked.
Contributors and Attributions
Remixed and/or curated from the following works:
Clark, M. A., Douglas, M., & Choi, J. (2018). 2.7.10 Review Questions and 2.7.11 Critical Thinking Questions . In Biology 2e . OpenStax (CC BY 4.0; Access for free at https://openstax.org/books/biology-2e/pages/1-introduction ).