The kinetochores appear at the centromeres, the mitotic spindle microtubules attach to kinetochores, and the centrosomes move toward opposite poles. Answer a occurs during metaphase, which happens before anaphase.
Answer c occurs during telophase, which happens after anaphase. Skip to main content. The Steps of Mitosis. Search for:.
The Steps of Mitosis Mitosis is an incredible process with precise steps and regulation. Mitosis: In Summary In prophase, the nucleolus disappears and chromosomes condense and become visible.
Practice Quiz Which of the following options shows the correct order of the steps of mitosis? Show Answer Answer a is correct.
The cleavage furrow forms because of the action of a contractile ring of overlapping actin and myosin filaments. As the actin and myosin filaments move past each other, the contractile ring becomes smaller, akin to pulling a drawstring at the top of a purse. When the ring reaches its smallest point, the cleavage furrow completely bisects the cell at its center, resulting in two separate daughter cells of equal size Figure 3. Figure 3: Mitosis: Overview of major phases The major stages of mitosis are prophase top row , metaphase and anaphase middle row , and telophase bottom row.
This page appears in the following eBook. Aa Aa Aa. What Are the Phases of Mitosis? Figure 1: Drawing of chromosomes during mitosis by Walther Flemming, circa What Happens during Prophase? What Happens during Prometaphase? Each microtubule is highly dynamic, growing outward from the centrosome and collapsing backward as it tries to locate a chromosome. Eventually, the microtubules find their targets and connect to each chromosome at its kinetochore , a complex of proteins positioned at the centromere.
The actual number of microtubules that attach to a kinetochore varies between species, but at least one microtubule from each pole attaches to the kinetochore of each chromosome. A tug-of-war then ensues as the chromosomes move back and forth toward the two poles. What Happens during Metaphase and Anaphase? Figure 2: Types of microtubules involved in mitosis. During mitosis, several types of microtubules are active. What Happens during Telophase? During telophase , the chromosomes arrive at the cell poles, the mitotic spindle disassembles, and the vesicles that contain fragments of the original nuclear membrane assemble around the two sets of chromosomes.
Phosphatases then dephosphorylate the lamins at each end of the cell. This dephosphorylation results in the formation of a new nuclear membrane around each group of chromosomes. When Do Cells Actually Divide? Figure 3: Mitosis: Overview of major phases. The major stages of mitosis are prophase top row , metaphase and anaphase middle row , and telophase bottom row.
Mitosis is the process of nuclear division, which occurs just prior to cell division , or cytokinesis. During this multistep process, cell chromosomes condense and the spindle assembles. The duplicated chromosomes then attach to the spindle, align at the cell equator, and move apart as the spindle microtubules retreat toward opposite poles of the cell. Each set of chromosomes is then surrounded by a nuclear membrane, and the parent cell splits into two complete daughter cells.
Cell Biology for Seminars, Unit 5. Topic rooms within Cell Biology Close. No topic rooms are there. Or Browse Visually. Student Voices. Metacentric chromosomes have the centromere located at or near the middle of the structure, resulting in two arms of equivalent or nearly so length.
These chromosomes appear V -shaped when observed during anaphase. In contrast, a telocentric chromosome has the centromere positioned very near one end and appears to migrate as a single arm. A majority of the chromosomes, however, are acrocentric , with the centromere positioned somewhere between the center and the end of the chromatid to yield an L -shaped structure in the microscope.
The onset of anaphase is triggered by specific biochemical changes that occur to regulate the division cycle through modulation of the enzyme cascade responsible for cell-wide protein phosphorylation. Deactivation of the mitosis-inducing protein kinase abbreviated MPF from the older term maturation-promoting factor activity by proteolysis of cyclin subunits serves to initiate anaphase.
Scientists speculate that the sister chromatids, which are held together along their length by a network of proteins, undergo a biochemical cleavage reaction that enables them to separate and begin the journey towards the spindle poles. Anaphase is characterized by two distinct processes to separate the sister chromatids and move them to opposite spindle poles in preparation for cell division.
The first process, termed anaphase A or early anaphase , occurs with the shortening of the kinetochore microtubules to translocate the chromatids away from the metaphase plate and towards the spindle poles. Anaphase B or late anaphase is manifested by a further separation of the spindle poles brought about by lengthening of the polar microtubule network. The overall contribution of each process to the final separation of the sister chromatids varies depending upon the organism being studied.
In animal cells, anaphase B begins soon after the chromatids split and terminates when the spindle has grown to approximately twice the metaphase length. In contrast, the cells of many lower eukaryotes exhibit a much larger separation distance during late anaphase, which can result in a spindle length increase up to 15 times the metaphase size.
When the chromosomes have completely migrated to the spindle poles, the kinetochore microtubules begin to disappear, although the polar microtubules continue to elongate. This is the junction between late anaphase and early telophase , the last stage in chromosome division. By the end of anaphase, each spindle pole has acquired an equivalent set of daughter chromosomes. The process of cytokinesis splitting of the daughter cells also begins during late anaphase with the initial formation of a contractile ring consisting of actin and myosin-II filaments positioned beneath the plasma membrane parallel to the metaphase plate.
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