Chapter 18 - The Cell Division Cycle Flashcards
The entire period between one M phase and the subsequent M phase is called what?
- anaphase
- prophase
- metaphase
- interphase
- G1 phase
Interphase
Correct; interphase consists of S phase plus the two gap phases, G1 and G2.
What must happen for a Cdk to be active?
- It must translocate from the cytoplasm to the nucleus.
- It must bind to its cyclin partner.
- It must increase in concentration at a specific time in the cycle.
- It must be switched on by proteolysis.
- It must dissociate from its bound cyclin.
It must bind to its cyclin partner
(A Cdk must bind its cyclin before it can become enzymatically active. A Cdk unbound to a cyclin does not retain kinase activity.)
The inactivation of M-Cdk leads to which of the following?
- exit from mitosis
- exit from S phase
- onset of mitosis
- onset of G2 phase
- onset of S phase
Exit from mitosis
(The degradation of M cyclin and inactivation of M-Cdk lead to the molecular events that take the cell out of mitosis and into interphase.)
The cell-cycle control system initiates chromosome segregation only after which of the following has occurred?
- The cell stops growing.
- DNA has been completely replicated and the chromosomes have decondensed.
- Cytokinesis is complete.
- The duplicated chromosomes are correctly aligned on the mitotic spindle.
- M phase is complete.
The duplicated chromosomes are correctly aligned on the mitotic spindle.
(Chromosome segregation takes place after the duplicated chromosomes are correctly attached to kinetochore proteins that interact with the microtubules of the mitotic spindle.)
What do cells do during G1 phase?
Choose one or more:
- replicate DNA
- separate sister chromatids
- repair DNA damage
- destroy cyclins
- Repair DNA damage
- Destroy cyclins
(During G1, cells grow and monitor the environment before committing to a new round of cell division. They can delay further progression through the cycle to repair damaged DNA. All Cdks are inactivated during G1, by cyclin degradation, to prevent an early entry into the cell cycle.)
Most of the diversity in the rates of cell division in the adult body lies in variations in the time that each cell spends in which phase(s)?
- S phase and M phase
- G1 phase and G2 phase
- S phase
- M phase
- G1 phase and G0 phase
G1 phase and G0 phase
Cells that divide every year or two spend the vast majority of that time—all but 12 to 24 hours—in G0 and G1.
The signal to commence DNA replication comes from which of the following?
- S-Cdk
- the destruction of M-Cdk
- ORC
- the destruction of Cdc6
S-Cdk
(S-Cdk, assembled and activated at the end of G1, initiates DNA replication by activation of the DNA helicases in the prereplicative complex, promoting the assembly of the proteins that form the replication fork.)
If DNA is damaged or incompletely replicated in S phase, the inhibition of which of these molecules prevents the cell from entering M phase?
- p53
- S-Cdk
- Cdc6
- Cdc25
- ORC
Cdc25
(For M-Cdk to be activated, the phosphatase Cdc25 must remove inhibitory phosphates from M-Cdk; inhibition of this activity can delay entry into M phase.)
In most respects, cell division is similar between plant and animal cells. Which of the following events occurs by a different mechanism in animal and plant cells?
- separation of sister chromatids
- condensation of chromosomes at the beginning of cell division
- separation of the cell into two daughter cells
- chromosomes being pulled apart by the microtubules of the mitotic spindle
- alignment of chromosomes in the center of the cell
Separation of the cell into two daughter cells
Cytokinesis, the separation of the cell into two new daughter cells, occurs differently in plant and animal cells.
True or False
Chromosomes condense and move to the center of the cell before sister chromatids separate in anaphase.
True
The chromosomes decondense in _______ before cytokinesis is complete.
telophase
What is the mitotic spindle made of?
- microtubules
- cohesins
- condensins
- actin and myosin
Microtubules
(The complete mitotic spindle is composed of these microtubules along with the various proteins that interact with them.)
Why does the activation of M-Cdk begin abruptly?
- M cyclin increases abruptly.
- The mitotic Cdk increases abruptly.
- Each M-Cdk complex can activate more M-Cdk.
- M cyclin is rapidly phosphorylated and thereby activated.
Each M-Cdk complex can activate more M-Cdk.
(The abrupt activation of M-Cdk depends on the removal of inhibitory phosphates by Cdc25; activated M-Cdk activates more Cdc25, thus promoting activation of additional M-Cdk through a positive feedback loop.)
The mitotic spindle begins to assemble in which phase of the cell cycle?
- telophase
- prometaphase
- prophase
- anaphase
- metaphase
Prophase
The mitotic spindle begins to assemble during the initial stage of mitosis once interphase has completed.
Microtubules capture chromosomes by binding specifically to which of the following?
- kinetochores on the sister chromatids
- telomeres on the condensed chromosomes
- condensins on the condensed chromosomes
- cohesins on the sister chromatids
Kinetochores on the sister chromatids
(Microtubules capture chromosomes by binding to kinetochores on the sister chromatids. Kinetochore proteins assemble at the centromere of each condensed chromosome.)
Which of the following occurs during metaphase?
- chromosomes being aligned under tension at the spindle equator
- nuclear envelope reassembly
- nuclear envelope breakdown
- chromosomes being captured by spindle microtubules
- chromosomes being condensed
Chromosomes being aligned under tension at the spindle equator
(During metaphase, chromosomes are aligned under tension at the spindle equator.)
What is the contractile ring made of?
- integrins
- cohesins
- microtubules
- actin and myosin
- condensins
Actin and myosin
(The sliding of actin filaments against myosin proteins generates the force needed to pinch off the plasma membrane and form two cells.)
In dividing plant cells, a new cell wall is formed between two sets of chromosomes via a structure called a phragmoplast, which is built by vesicles largely originating from which organelle?
- vacuole
- endoplasmic reticulum
- vesicles from the broken-down nuclear envelope
- Golgi apparatus
- chloroplast
Golgi apparatus
(Correct; these membrane-enclosed vesicles fuse to form a disclike, membrane-enclosed structure that expands until it reaches the plasma membrane and original cell wall.)
When a cell is acutely injured, it usually dies by which process?
- apoptosis
- endocytosis
- phagocytosis
- necrosis
Necrosis
Necrotic cells typically swell and burst, causing local inflammation.
Which of the following statements is false?
- Some death-inhibiting members of the Bcl2 family inhibit apoptosis by blocking cytochrome c release from mitochondria.
- Bax and Bak are death-promoting members of the Bcl2 family that induce the release of cytochrome c from mitochondria into the cytosol.
- Some Bcl2 family members promote apoptosis, whereas others inhibit apoptosis.
- The death-promoting members of the Bcl2 family include Bcl2 itself.
The death-promoting members of the Bcl2 family include Bcl2 itself.
(Bcl2 inhibits apoptosis. Thus, it cannot be considered to be death-promoting.)
Which of the following statements describes how growth factors stimulate animal cell enlargement?
- They stimulate microtubule polymerization.
- They stimulate protein degradation.
- They stimulate intracellular protein synthesis.
- They stimulate an influx of extracellular water into the cytosol.
They stimulate intracellular protein synthesis.
Growth factors increase the rate of protein synthesis and decrease the rate of protein degradation.
What are example of active Cdk?
- Cdk bound to cyclin
- Threonine in T loop phosphorylated
(Binding of a cyclin protein and phosphorylation of the T loop activate the Cdk.)
What are examples of inactive Cdk?
- T loop in active site
- Cdk alone
- Cdk/cyclin bound to p27
(Cdk inhibitors inhibit Cdk.)
Cdk inhibitors inhibit the function of cyclin-dependent protein kinases. Different inhibitors display varying mechanisms of Cdk inhibition. Which of the following might a Cdk inhibitor block in order to block Cdk function?
Choose one or more:
- movement of the T loop into the active site
- cyclin binding
- ATP binding
- substrate binding
- cyclin binding
- ATP binding
- substrate binding
(Cdk inhibitors could block cyclin, ATP, or substrate from binding to reduce activity of Cdk.)