5 Characteristics cell cycle

The cell cycle refers to the series of events that occur in a cell as it grows, prepares for division, and divides into two daughter cells.

What is the cell cycle?

The cell cycle is a type of asexual reproduction that is identified as the life cycle of a cell. In this cycle there is an ordered set of stages of growth and development that the cell presents from its formation by division of a mother cell, through its reproduction where the cell divides to create two daughter cells and each one receives a copy of the duplicated material. , until finally each daughter cell is surrounded by its own outer membrane.

Characteristics cell cycle

Here are the key characteristics of the cell cycle:

  1. Interphase: The cell cycle begins with interphase, which is divided into three phases: G1 (Gap 1), S (Synthesis), and G2 (Gap 2). During G1 phase, the cell grows, carries out its normal functions, and prepares for DNA replication. In S phase, DNA replication occurs, resulting in the synthesis of identical copies of the cell’s chromosomes. G2 phase is a period of further growth and preparation for cell division.
  2. Mitosis: After interphase, the cell enters mitosis, which consists of four stages: prophase, metaphase, anaphase, and telophase. During prophase, the chromatin condenses into distinct chromosomes, the nuclear envelope breaks down, and the mitotic spindle begins to form. In metaphase, the chromosomes align along the equator of the cell. Anaphase follows, during which the sister chromatids separate and move towards opposite ends of the cell. Finally, in telophase, the nuclear envelope reforms, the chromosomes decondense, and the mitotic spindle disassembles.
  3. Cytokinesis: Cytokinesis is the final stage of the cell cycle, during which the cytoplasm divides to form two separate daughter cells. In animal cells, a cleavage furrow forms, and the cell membrane pinches inward to separate the cytoplasm. In plant cells, a cell plate forms along the equator of the cell, which develops into a new cell wall, ultimately dividing the cytoplasm.
  4. Control Mechanisms: The cell cycle is tightly regulated by various control mechanisms to ensure accurate cell division. Checkpoints are key regulatory points throughout the cell cycle that monitor DNA integrity, cell size, and other factors. If any abnormalities are detected, the cell cycle can be paused, allowing time for repairs or triggering cell death if necessary.
  5. Variation in Cell Cycle Length: The duration of the cell cycle can vary depending on the type of cell and its specific function. Some cells, such as rapidly dividing embryonic cells, have short cell cycles, while others, like neurons, can have long cell cycles or even exit the cell cycle permanently.

In summary, the cell cycle is a highly regulated process that consists of interphase (G1, S, and G2 phases), mitosis (prophase, metaphase, anaphase, and telophase), and cytokinesis. It allows cells to grow, replicate their DNA, and divide into two daughter cells. Control mechanisms ensure the accuracy of cell division, and the length of the cell cycle can vary depending on cell type and function.

Types of cell cycle

In eukaryotic cells, that is, those that have a differentiated nucleus and are found in animal, plant, fungal and protist cells, the cell cycle consists of two main stages called interphase and mitotic phase (mitosis and cytokinesis ) .

For its part, in prokaryotic cells , those that belong to bacteria and archaea, the cell cycle is divided into periods B, C and D, where B extends from the end of cell division to the beginning of replication. of DNA.

Eukaryotic cells

The interface is made up of stages G1, S and G2. At this stage, the cell performs its specific functions, and if it wishes to continue cell division, it begins by replicating its DNA.

G1 phase .

GAP 1 or first interval phase, is the first phase where the cell prepares to divide. It includes the period between the end of mitosis and the beginning of DNA synthesis, which is why it takes approximately 6 to 12 hours.

At that time, there is cell growth with protein and RNA synthesis. In addition to the cell physically growing in size and mass, it copies the organelles and prepares molecular components that it will later require in the following stages.

In addition, the G1 phase serves as a very important checkpoint where cells with damaged DNA are separated so that they cannot be synthesized in this way and alter the process.

Phase S.

The S phase, the second of the cycle, is characterized by DNA synthesis. Here the chromosome is duplicated and two identical chromatids are formed. It also duplicates a microtubule organizing structure called the centrosome. With DNA duplication, there is an extra and complete supply of all the genetic material; That is, the nucleus stores twice as many proteins and DNA.

The S phase has an average duration between 10 and 12 hours; which occupies approximately half the time of the cell cycle in a basic eukaryotic mammalian cell.

G2 Phase.

GAP 2 or second interval phase, lasts between 3 and 4 hours. Here the cell grows larger and produces proteins and organelles, as well as begins to reorganize its contents to prepare for mitosis. The G2 phase concludes when mitosis begins.

Cell cycle and cancer.

Cancer is closely related to the cell cycle, since it is basically a disease of uncontrolled cell division.

 

The development and progression of cancer in an organism is usually associated with alterations in some stage of the cell cycle. There are cell cycle inhibitors that prevent cell division when conditions are not suitable for it to take place. A failure or error in these inhibitors can cause cancer of different types.

cell death

During the cell cycle, cells can be eliminated at any part of the process. Elimination depends on internal mechanisms or external factors. Three types of cell death are identified in eukaryotic cells: apoptosis, autophagy and necrosis:

  • Apoptosis : Occurs during the early stages of development to eliminate unnecessary cells that have been irreversibly damaged.
  • Autophagy : It is the way in which cells recycle their components. Portions of the cytoplasm are enclosed within a double-membrane vacuole and digested by lysosomal hydrolases.
  • Necrosis : It is the pathological death of the cells or tissues of the body. There is rupture of the plasma membrane and loss of intracellular material. Necrosis is irreversible in any of its forms and is divided into two types: oncotic necrosis and apoptotic necrosis.
  • Oncotic necrosis : Large areas of the organ or organs are affected, and the necrotic cells send signals to the body to initiate inflammatory reactions.
  • Apoptotic necrosis : It develops at the level of individual cells and necrotic debris forms inside the phagocytes or macrophages, or neighboring parenchymal cells.

Prokaryotic cells

The vast majority of prokaryotic cells have a single copy of each gene, which is why they are called haploid. The genomes of these cells are compact and have little repetitive DNA.

Unlike eukaryotes where the DNA is located within the nucleus, the DNA of prokaryotes is found in a circular chromosome in the nucleoid within the cytoplasm; which is why transcription and translation occur simultaneously.

The cell cycle of prokaryotic cells consists of a long period of growth, where the cell replicates its DNA, followed by a form of cell division called binary fission.

In binary fission, bacteria perform cell division. It is similar to mitosis, but its purpose is different. It is an asexual reproduction where a prokaryotic organism duplicates its genetic material , DNA, and then divides into two parts (cytokinesis), where each of these has a copy of DNA.

Mitotic phase (M phase)

The M phase involves two distinct processes related to division: mitosis and cytokinesis .

Mitosis is the state of cell division. That is, a process in which a single cell divides into two identical daughter cells. Each chromosome becomes a pair to separate completely until ending up as two (identical) daughter cells with a complete set of DNA.

The main purpose of mitosis is the growth and replacement of worn-out cells, since if any damaged cells are part of the process, it could cause serious modifications to the DNA and thus lead to genetic disorders.

Mitosis is divided into prophase, metaphase, anaphase, telophase and cytokinesis .

Phases of Mitosis.

 

  • Prophase: Chromosomes condense into X-shaped structures and can be easily recognized in the cell nucleus. These chromosomes pair so that both copies of chromosome 1 are together and both copies of chromosome 2 are together. The pairs of centrioles separate towards opposite poles, and as they separate, fibers are observed that form a structure called the mitotic spindle, which consists of microtubules and other proteins.
  • Metaphase: The chromosomes line up perfectly end to end along the center of the cell. The centrioles are now at opposite poles of the cell and the fibers belonging to the mitotic spindle adhere to each of the sister chromatids.
  • Anaphase: In anaphase, sister chromatids are then separated by the mitotic spindle to opposite poles. The chromosomes reach their maximum level of condensation.
  • Telophase: In this last phase of mitosis, the mitotic spindle fibers disappear and a membrane forms around each set of chromosomes to create two new nuclei.

Cytokinesis

Cytokinesis is when the cytoplasm of a single cell divides into two daughter cells where each contains a complete set of chromosomes within a nucleus .

In plant cells, cytokinesis is carried out in a very different way, because the rigid walls of the cells prevent them from dividing in two as in animal cells. In this case, vesicles that come from the Golgi apparatus and are loaded with carbohydrates, line up along the middle of the cell (equator) between the two nuclei.

When the vesicles fuse, they produce a structure called a cell plate, very similar to a compartment or flattened sac that is surrounded by a membrane and filled with carbohydrates with a viscous and sticky texture.

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