Is DNA condensed in the S phase

Cell cycle

We will deal with the cell cycle in this article. We will explain to you what is meant by the cell cycle and what processes it consists of. This article belongs to our field of biology.

For animals, humans and plants to survive, it is very important to form new cells. This process is understood in biology as the cell cycle. The cell cycle usually consists of interphase and mitosis (cell division). What is behind this will be explained in more detail in a moment. The following list shows the course of a cell cycle in advance.

Cell cycle sequence:

  1. G1-Phase
  2. S phase
  3. G2-Phase
  4. Prophase
  5. Metaphase
  6. Anaphase
  7. Telophase

After the seventh point (telophase) the G often begins again1-Phase.

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Cell cycle: interphase

The cell cycle starts with the interphase. For a better overview, this is subdivided into G1-Phase, S-phase and G2-Phase.

G1-Phase / Gap Phase:

In the G1Phase of the cell cycle - sometimes called the gap phase - the cell grows very strongly and prepares for cell division. There is an increase in protein synthesis; Proteins are produced which are required for the distribution apparatus of the chromosomes. In addition, histones and non-basic proteins are formed to enclose the DNA and there is a sharp increase in RNA synthesis. The centrioles divide.

The nucleus can be seen and each chromosome consists of a chromatid. Above all, however, this is the phase in which the cell reaches its typical nucleus-plasma ratio and performs its specific function until a certain nucleus-plasma ratio is exceeded. The G1- The phase usually lasts several hours (1 to 12 hours). Since there is no synthesis of DNA, this phase is also known as the gap phase.

S-phase / synthesis phase:

"Replication" of the DNA takes place in the S phase / synthesis phase of the cell cycle. This means that at the end of the process, the cell's genetic material has been doubled. Each chromosome now has two identically structured subunits (chromatids). During the next mitosis, these two will separate and distribute to the daughter cells. The S phase takes about 7-8 hours.

G2 phase:

The G2 phase represents the transition to mitosis; all requirements for core division are now in place. The transitions into the individual phases are controlled by special proteins. In tissues, the cell contacts to the neighboring cells loosen, the cell rounds off and enlarges through fluid absorption. Increasingly, RNA molecules and cell division-specific proteins are being synthesized in order to prepare for the subsequent mitosis. The G2-Phase lasts around four hours. This completes the interphase of the cell cycle.

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Cell cycle: mitosis

In the cell cycle, the interphase is followed by mitosis. In principle, one can say: unicellular organisms multiply when a cell divides into two daughter cells. These daughter cells then grow to the size of the original cell. This creates two daughter cells that are genetically identical to the original cell. The process of division (nucleus division) is called mitosis in biology or genetics.

The chromosome set of each daughter cell corresponds to that of the mother cell; because of this, the daughter cells are genetically identical. This assumes that half of the chromosomes and not whole chromosomes pass to the subsequent cells during mitosis. How long a mitosis lasts depends on the organism and the cell type. However, mitosis usually lasts a few hours.

In the field of mitosis, two other terms are often used, which, however, do not belong directly to mitosis and are therefore only mentioned here in passing: Cytokinesis and cell cycle. During cytokinesis, the cytoplasm is divided. A cell cycle, on the other hand, is the process from the end of mitosis with the formation of daughter cells to the end of a subsequent mitosis.

Cell cycle: process of mitosis

The process of mitosis takes place in different steps, which we would like to deal with in this section. As a rule, a distinction is made between the following phases in mitosis: prophase, metaphase, anaphase and telophase.

Prophase:

The prophase is the first phase of mitosis and can take up to five hours, depending on the organism and cell type. In prophase the chromosomes contract strongly. They condense and become visible through this process under the light microscope. Before division, each chromosome consists of two identical strands (called chromatids), which for the most part separate from each other and are only held together by a so-called centromere.

Now the development of the mitotic spindle begins - sometimes also called the core division spindle, the spindle poles move apart and the nuclear envelope and the nuclear corpuscles disintegrate. The spindle fibers now attach themselves to the centromeres of the chromatids. The chromosomes are exposed at the end of the prophase.

Metaphase:

The chromosomes are arranged in one plane (equatorial plane) and the sister chromatids point to the opposite spindle poles. In the metaphase it is possible to differentiate the different chromosomes according to shape and size. The spindle fibers attach themselves to the centrometer from both sides.

Anaphase:

The chromatids are first completely separated from each other by shortening the spindle fibers and the support of caulking fibers and then drawn to the two opposite poles. This gives each pole a similar set of chromatids. The duration of the anaphase varies widely from 2 to 20 minutes.

Telophase:

In the telophase the chromatids unscrew and unfold. You will then go into the working form. Nuclear corpuscles and nuclear membrane form anew. After cell division, each daughter cell has the same number of chromosomes as the parent cell.

After the end of mitosis, cytokinesis follows, during which the cytoplasm is divided. Two daughter cells have emerged from one mother cell. This completes the cell cycle.

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