Mol Bio of Cell Chapter 14
Terms in this set (47)
What process is responsible for satisfying the third tenet of the Cell Theory, which states that new cells originate from other living cells?
You are carrying out experiments in cell fusion by fusing together cells at different stages of the cell cycle. You then observe the behavior of each nucleus residing in the combined cytoplasm of the two cells. Which of the following responses would occur if you fused a G1 cell to a cell in the M phase?
The G1 nucleus undergoes premature chromosomal condensation to form a set of elongated compacted chromosomes
Based on cell activities readily visible in the light microscope, there are two major cell cycle phases, ________ and __________.
M phase, interphase
What allows the interaction between the mitotic spindle and the chromosomes to occur?
nuclear envelope breakdown
What is the main difference in microtubule dynamics between metaphase and anaphase?
Subunits are added to the plus end during metaphase and lost from the plus ends during anaphase
What gives rise to the plasma membranes of the two daughter cells formed during cytokinesis?
membranes of the vesicle-derived tubule network that forms the cell plate
How does securin get its name?
Securin secures the attachment between sister chromatids.
What is the average length of interphase?
There is not a good average since it may extend for days, weeks or longer depending on the cell type and the conditions.
Which of the following statements about checkpoints is NOT true?
Checkpoint mechanisms are messy and are not always effective.
Which of the following statements about checkpoints is true?
They halt the progress of the cell cycle, if DNA is damaged.
They halt the progress of the cell cycle, if DNA replication has not been completed.
Many of the proteins of the checkpoint machinery have no role in normal cell cycle events.
Once a fission yeast cell passes START, the cell is committed to DNA replication. What is responsible for activating cdc2 at this time?
one or more G1 cyclins
What external stimulation is required by mammalian cells to progress through the cycle after they have passed the restriction point?
none after the restriction point is passed
What triggers the entry of a cell into mitosis?
The removal of inhibitory phosphate groups from Cdk1 by the Cdc25 phosphatase.
Place the following events in one of the arrest pathways in the correct order starting with a G2 cell detecting the presence of DNA damage caused by UV irradiation.
1 - The cell is arrested in G2.
2 - The Cdc25 molecule becomes a target for a special adaptor protein that binds to the Cdc25 phosphatase in the cell cytoplasm.
3 - Cdk1 in the nucleus remains in an inactive state since its inhibitory phosphate groups cannot be removed by Cdc25.
4 - Chk1 phosphorylates Cdc25 on a particular serine residue.
5 - Cdc25's phosphatase activity is inhibited and its reimportation into nucleus is prevented.
6 - ATR kinase is activated and phosphorylates a checkpoint kinase, called Chk1.
7 - ATR kinases are recruited to sites of protein-coated, single-stranded DNA, like those created as UV-damaged DNA is repaired.
7 - 6 - 4 - 2 - 5 - 3 - 1
What would be likely to happen to cultured cells if you were able to treat them with an inhibitor that specifically depressed the activity of Cdk?
The cells would remain in G2 and would not move toward mitosis.
During which part of the cell cycle are SCF complexes active?
From late G1 through early mitosis.
Mouse embryos that lack the genes encoding Cdks 2, 3, 4 and 6, four cell-cycle Cdks, are capable of developing to a stage with fully-formed organs, although the animal does not survive to birth. Which of the following statements based on these results is true of these cells?
Cells taken from such embryos are capable of proliferating in culture, although more slowly than normal cells.
Even though Cdks 2, 3, 4 and 6 are normally expressed at specific times during the mammalian cell cycle, Cdk1 is able to cover for their absence.
Cdk1 is the only Cdk required to drive a mammalian cell through all of the stages of the cell cycle.
What distinguishes prophase from the other stages of mitosis?
The chromosomes are not yet attached to microtubules.
Microtubule elongation and shortening while chromosomes are being moved to the center of the dividing cell are the result of the _____ or ______, respectively, of subunits at the _____ end of the microtubules.
gain, loss, plus
Where can motor proteins be found in mitotic cells?
At spindle poles, along spindle fibers and within kinetochores and chromosome arms.
Ubiquitination and destruction of securin at the end of ________ releases an active protease called ______ that had been bound by its securin inhibitor and proceeds to cleave a key _____ subunit, leading to the separation of sister chromatids.
metaphase, separase, cohesin
Near the end of mitosis, the Cdc20 subunit of APC is replaced by the other substrate-targeting subunit, Cdh1. What substrate is then recognized by APC and ubiquitinated?
What advantage may be gained from the slow movement of chromosomes toward the poles during mitosis?
It may ensure that chromosomes segregate accurately without entanglement.
What is the primary difference in microtubule dynamics between metaphase and anaphase?
Subunits are added to microtubule plus ends during metaphase and lost from them during anaphase.
How would the location of the array of actin filaments involved in animal cell cytokinesis be described?
In the cortex and under the furrow in a cleaving cell aligned parallel to the furrow.
It is generally agreed that the position of the cleavage furrow is determined by the anaphase mitotic spindle. Through what mechanism does the spindle appear to do this?
The spindle causes the activation of RhoA in a narrow ring within the cortex.
According to research in sea urchins, where does the contractile ring form?
It forms in a plane midway between the spindle poles, even if one of the poles is displaced by a microneedle inserted into the cell.
A cell that is entering the M phase of the cell cycle is:
either haploid or diploid, always with duplicated chromosomes.
A culture of cells is given 3H-thymidine for 30 minutes; then a sample of the cells is fixed and examined by autoradiography. It is found that:
none of the cells engaged in mitosis have incorporated the labeled thymidine into their chromosomes.
During which phases of the cell cycle do the chromosomes exist in a doubled state?
G2 and early M
Liver cells are highly specialized, but when the liver is damaged or parts of it are removed surgically, the tissue grows. Liver cells fall into which category of cells?
cells that can be induced to enter the S phase
Throughout interphase, __________ are synthesized at a relatively constant rate, whereas ________ are synthesized only during the S phase.
most major proteins, histones
If a cell in the G1 phase is fused with a cell in the S phase, then
the G1 nucleus will enter the S phase
Cyclin concentrations are highest during which periods of the cell cycle?
late G2 and early M
Cyclin is to MPF in embryonic development as ? is to cyclin-dependent kinases in fission yeasts.
The product of the cdc2 gene is
A mutation in the gene that codes for p53 can result in
loss of an inhibitor protein, p21, loss of a transcription factor and uncontrolled cell growth and cancer.
Which of the following structures is not a feature of the mitotic chromosome?
During which of the following mitotic phases are chromosomes dispersed the most?
The mitotic spindle assembly:
takes place in the cytoplasm.
Which of the following are experimentally observed possibilities to explain chromosomal movement during anaphase?
Depolymerization of spindle microtubules occurs at the minus ends.
Depolymerization of spindle microtubules occurs at the kinetochores.
Microtubule disassembly establishes the rate of chromosomal movement.
Which of the following experimental observations (some real, some contrived) would not be consistent with our current understanding of cytokinesis?
Anti-actin antibodies injected into dividing cells have no effect on cytokinesis.
The cleavage furrow is to animal cells as the _________ is to plant cells.
The life cycle of mosses is characterized by an "alternation of generations," where the small, haploid gametophyte produces gametes, which fertilize and give rise to the tall sporophyte generation. What type of life cycle is this?
Recombination events between homologous chromosomes during meiosis is thought to begin during
Which stage of cell division provides visual evidence of Mendel's law of independent assortment?
meiotic anaphase I
Which of the following statements relating to the incidence of trisomy 21 in humans is correct?
Errors occurring in chromosomal segregation during meiosis I are commoner than errors in meiosis II.
Trisomy 21 babies are born more frequently to older mothers.
More human oocytes are aneuploid than those of other mammals that have been studied.
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