Anaphase is the third phase of cell division and immediately follows metaphase. During anaphase, the sister chromatids separate.
What happens in anaphase 1 and 2 of mitosis? – Process
You were told in the relevant article that metaphase is considered complete once all chromosomes have reached their position in the equatorial plane. This is where anaphase begins. The sister chromatids, which were previously connected as chromosomes, are pulled apart.
This is done using the kinetochore microtubules attached to the centromeres. The enzyme separase, which dissolves the cohesin connections between the sister chromatids, has a supporting effect. These are also located in the centromere.
Figure 1: The anaphase, source: wikipedia.org
The figure shows you how the chromatids using the microtubules be drawn to the poles. During the anaphase, two phases can be specifically distinguished. The first is just about the chromatids being pulled to their respective poles. This occurs via depolymerization of the kinetochore microtubules.
Under polymerization refers to the assembly of individual building blocks (monomers) into larger complexes (polymers).
Examples of polymers are microtubules. They are composed of several units of the protein tubulin and thus form tubes that can vary in length. The breakdown of polymers into monomers is referred to as depolymerization.
Kinetochores are structures around the centromeres, to which the spindle fibers of microtubules attach.
As part of the cell’s cytoskeleton, microtubules are normally permanently polymerized and depolymerized. Here, GTP plays an important role, which is then hydrolyzed to GDP after polymerisation on the microtubules. Depolymerization only takes place in the presence of GDP.
GTP (guanosine triphosphate) is a high-energy molecule that z. B. arises in the citric acid cycle. Energy is required for the polymerisation, which is released by the hydrolysis of GTP to GDP (guanosine diphosphate).
The second phase is characterized by the fact that not only do the chromatids move apart during this time, the spindle poles also bring more and more distance between them. As a result, the cell takes on an elongated shape. In this case, interpolar microtubules, which connect the two poles with one another, become longer as a result of polymerisation.
Figure 2: The second part of anaphase – the poles move apart. Source: doccheck.flexikon.com
This figure shows you how the cell is slowly getting wider as the poles move away from each other.
This process is supported, among other things, by a kinesin motor. In addition, dynein works. In the figure you can see that in the middle of the cell as small red dots. Among other things, both enzymes play an important role when it comes to the transport of particles in the cell. In this case, they ensure that the two poles are so far apart that two cells can actually form from one.
Kinesin and dynein are motor proteins because they enable intracellular transport. To do this, they migrate along microtubules as if on rails and can also move other molecules in the process.
Anaphase – definition
In summary, anaphase can be defined as follows:
In anaphase, the sister chromatids are pulled apart by the kinetochore microtubules. A distinction is made between the first phase, in which the chromatids move away from each other, and the second phase, in which the poles also move away from each other.
Recognizing the anaphase – explanation
In this section you can now look at two microscopic images showing cells in anaphase.
Figure 3: The anaphase under the microscope. Source: microscopy-forum.de
This figure shows you the cell in the middle, which is in anaphase. It is particularly characteristic of this that you can already see two areas in a cell where chromosomes are located. You can also theoretically recognize the poles here. As you can see, the chromatids are pulled toward the pole at the centromere. Therefore, they all focus on this one specific point, which is not marked, but because of the arrangement clearly visible becomes.
The best way to recognize anaphase under the microscope is to look for the chromatids that migrate towards one point. It is also a condition that the centromeres point outwards. Often you can even assume that at least two areas with chromosomes are recognizable.
Figure 4: The anaphase compared to the telophase. Source: illumina-chemie.de
In this figure, anaphase (A) and telophase (T) are labeled. This illustration should make the difference clear to you again.
While the chromatids are still clearly visible in the anaphase, loose chromatin is formed again in the telophase, which can then begin gene expression. Also, poles are no longer evident in telophase, which is still the case in anaphase.
The best way to distinguish the two phases is to look for recognizable poles and look at the shape of the chromatin. Is it still clearly visible as chromatids or already loose chromatin resembling a ball of yarn? If the latter is the case, it is already the telophase.
Anaphase Mitosis – The Essentials
- Anaphase is the third phase of cell division.
- During anaphase, the sister chromatids separate from each other. The separation takes place with the enzyme Separase.
- The kinetochore microtubules are depolymerized to pull the sister chromatids toward the poles.
- The polars diverge using a kinesin motor and dynein.
- Anaphase can be seen under the microscope by looking for discernible poles for the chromatids to align with. Two chromatid clusters are often visible.
- During anaphase, the chromatin is still clearly visible.