Which one of the following events occurs during M phase? In the M phase, one parent cell physically divides into two daughter cells. This includes the physical separation of the duplicated genome (termed mitosis) and the subsequent separation of the cytoplasm by a process called cytokinesis.
What are the two major events of the M phase?
It is crucial that the two major events of M phase—nuclear division (mitosis) and cytoplasmic division (cytokinesis) —occur in the correct sequence (see Figure 18-1). It would be catastrophic if cytokinesis occurred before all of the chromosomes had segregated during mitosis. At least two mechanisms seem to prevent this catastrophe. First, the cell-cycle control systemthat activates proteins required for mitosis is thought to inactivate some of the proteins required for cytokinesis; presumably for this reason, cytokinesis cannot occur until M-Cdkis inactivated at the end of mitosis. Second, after the mitotic spindlehas segregated the two sets of chromosomes to opposite poles of the cell, the residual central region of the spindle is required to maintain a functional contractile ring(see Figure 18-4); thus, until the spindle has separated the chromosomes and formed a central spindle,the ring cannot divide the cytoplasmin two.
What are the two critical events that must be completed in interphase before M phase begins?
Two critical events must be completed in interphasebefore M phasebegins—replication of the DNAand, in animal cells, duplication of the centrosome. DNA is duplicated so that each new daughter cell inherits an identical copy of the genome, while the centrosome is duplicated to help initiate the formation of the two poles of the mitotic spindleand to supply each daughter cell with its own centrosome . As we discuss later, after the chromosomes have been segregated in late mitosis, the microtubules that emanate from the two centrosomes signal to the cell cortexto help establish the plane of cytoplasmic division. This ensures that the division occurs exactly midway between the two separated groups of chromosomes (see Figure 18-4).
What cycle is the centrosome in?
The centrosome cycle. The centrosome in a proliferating animal cell duplicates in interphase in preparation for mitosis. In most animal cells, a centriole pair (shown here as a pair of dark greenbars) is associated with the centrosome matrix (light green)(more...)
What is the process of centrosomes being separated?
The process of centrosomeduplication and separation is known as the centrosome cycle. During interphaseof each animal cell cycle, the centrioles and other components of the centrosome are duplicated (by an unknown mechanism) but remain together as a single complexon one side of the nucleus(Figure 18-5). As mitosisbegins, this complex splits in two, and each centriolepair becomes part of a separate microtubuleorganizing center that nucleates a radial array of microtubules called an aster(Figure 18-6). The two asters move to opposite sides of the nucleus to initiate the formation of the two poles of the mitotic spindle. When the nuclear envelopebreaks down (at prometaphase),the spindle captures the chromosomes; it will separate them toward the end of mitosis (Figure 18-7). As mitosis ends and the nuclear envelope re-forms around the separated chromosomes, each daughter cell receives a centrosome in association with its chromosomes.
How to know if a cell is in M phase?
The first readily visible sign that a cell is about to enter M phaseis the progressive compaction of the replicated chromosomes, which become visible as threadlike structures —a process called chromosome condensation. In humans, for example, each interphasechromosomebecomes compacted after replication into a mitotic chromosomethat is about 50 times shorter (Figure 18-2). As discussed in Chapter 4, proteins called condensinsdo the work of chromosome condensation. Activated M-Cdkphosphorylates some of the condensin subunits, triggering the assembly of condensin complexes on DNAand, thereby, the progressive condensation of the chromosomes. The condensins can use the energy of ATP hydrolysis to promote DNA coiling in a test tube, and they are thought to do the same in cells during chromosome condensation. By a mechanism that is still poorly understood, they eventually produce fully condensed mitotic chromosomes, with each of the two sister chromatids organized around a linear central axis, where the condensin complexes are concentrated (see Figure 18-2).
What is the process of cell division?
Cell division occurs during M phase, which consists of nuclear division (mitosis) followed by cytoplasmic division (cytokinesis). The DNAis replicated in the preceding S phase; the two copies of each replicated chromosome(called sister chromatids) remain glued together by cohesins. At the start of M phase, cohesin-related proteins called condensins bind to the replicated chromosomes and progressively condense them. A microtubule-based mitotic spindleis responsible for chromosome segregation in all eucaryotic cells. The mitotic spindle in animal cells develops from the microtubule asters that form around each of the two centrosomes produced when the centrosomeduplicates, beginning in S phase; at the onset of M phase, the duplicated centrosomes separate and move to opposite sides of the nucleusto initiate the formation of the two poles of the spindle. An actinand myosin-based contractile ringis responsible for cytoplasmic division in animal cells and in many unicellular eucaryotes, but not in plant cells.
What are the stages of mitosis?
The five stages of mitosis—prophase, prometaphase, metaphase, anaphase, and telophase —occur in strict sequential order, while cytokinesisbegins in anaphase and continues through telophase. Light micrographs of cell divisionin a typical animal cell and a typical plant cell are shown in Figures 18-8and 18-9, respectively. During prophase, the replicated chromosomes condense in step with the reorganization of the cytoskeleton. In metaphase, the chromosomes are aligned at the equator of the mitotic spindle, and in anaphase they are segregated to the two poles of the spindle. Cytoplasmic division is complete by the end of telophase, and the nucleusand cytoplasmof each of the daughter cells then return to interphase, signaling the end of M phase.
Which phase of the cell cycle contains the most DNA?
A cell contains the most DNA after S phase of the cell cycle. A cell is smallest in size after M phase of the cell cycle. Growth occurs in G1, S, and G2 phases of the cell cycle. A cell does not enter mitosis until it has completed DNA synthesis.
Why do cells engage molecular brakes?
In response to a defect or a delay in a cell-cycle event, cells engage molecular brakes to arrest the progression of the cell cycle at various checkpoints, to allow time for completion or repair.
What is the statement of the cell cycle?
Explain your answer. A. Statement 1: Generally, in a given organism, the S, G2, and M phases of the cell cycle take a defined and stereotyped amount of. time in most cells. B. Statement 2: Therefore, the cell-cycle control system operates.
What triggers the onset of cytokinesis?
a. Activated M-Cdk triggers the onset of cytokinesis.
What are checkpoints in cell cycle control?
a. Checkpoints of cell-cycle control system ensure that the environment is favorable for the cell to initiate DNA replication.
What is the term for the early metaphase?
Prometaphase is often referred to as “late prophase.” (Though it’s also sometimes called “early metaphase” or referred to as a distinct phase entirely!) Regardless, some really important things occur during prometaphase that propel cell division along and that help explain what happens in metaphase.
What happens during prometaphase?
The short version of what happens during prometaphase is that the nuclear membrane breaks down .
What Is Mitosis?
Mitosis is a process that occurs during the cell cycle. The role of mitosis in the cell cycle is to replicate the genetic material in an existing cell—known as the “parent cell”—and distribute that genetic material to two new cells, known as “daughter cells.” In order to pass its genetic material to the two new daughter cells, a parent cell must undergo cell division, or mitosis. Mitosis results in two new nuclei—which contain DNA—that eventually become two identical cells during cytokinesis .
What is the line that divides the sister chromatids down the middle of the cell called?
This imaginary line dividing the cell down the middle is called the metaphase plate or equatorial plane .
How many phases does mitosis occur in?
In order to accomplish this goal, mitosis occurs in four discrete, consistently consecutive phases: 1) prophase, 2) metaphase, 3) anaphase, and 4) telophase . We have an overview of mitosis here, which is more of an intro to what mitosis is and how it works. If you're a little shaky on mitosis still, that's definitely where you should start.
What is interphase in biology?
We can think of interphase as a transitional phase. Interphase is when the parent cell prepares itself for mitosis. This phase isn’t considered part of mitosis, but understanding what happens during interphase can help the steps of mitosis make a little more sense.
What is the purpose of mitosis?
The main purpose of mitosis is to accomplish cell regeneration, cell replacement, and growth in living organisms. Mitosis is important because it ensures that all new cells that are generated in a given organism will have the same number of chromosomes and genetic information. In order to accomplish this goal, mitosis occurs in four discrete, consistently consecutive phases: 1) prophase, 2) metaphase, 3) anaphase, and 4) telophase .
