뒤로Phases of the Eukaryotic Cell Cycle and Mitosis
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Phases of the Eukaryotic Cell Cycle and Mitosis
Introduction
The eukaryotic cell cycle is a series of stages that cells undergo to grow and divide. Mitosis is the process by which a eukaryotic cell separates its duplicated chromosomes into two identical sets, leading to the formation of two daughter cells. The cell cycle is divided into interphase (including G0 and G1), and the mitotic (M) phase, which is further subdivided into several stages.
Main Phases of the Cell Cycle
G0 of Interphase: A resting or quiescent phase where the cell is not actively preparing to divide. Cells may remain in G0 temporarily or permanently, depending on their type and function.
Prophase: The first stage of mitosis, where chromatin condenses into visible chromosomes, and the mitotic spindle begins to form. The nuclear envelope starts to break down.
Prometaphase: The nuclear envelope completely dissolves, and spindle fibers attach to the kinetochores of chromosomes. Chromosomes begin moving toward the metaphase plate.
Metaphase: Chromosomes align at the cell's equatorial plane (metaphase plate), with spindle fibers attached to each sister chromatid.
Anaphase: Sister chromatids are separated and pulled toward opposite poles of the cell by the spindle fibers.
Telophase: Chromatids reach the poles, nuclear envelopes reform around each set of chromosomes, and chromosomes begin to decondense.
Cytokinesis: The cytoplasm divides, resulting in two genetically identical daughter cells. In animal cells, this occurs via cleavage furrow formation; in plant cells, a cell plate forms.
Key Features of Each Phase
Phase | Main Events |
|---|---|
G0 of Interphase | Cell is not actively dividing; may perform normal functions or prepare for division if re-entering the cycle. |
Prophase | Chromosomes condense; spindle apparatus forms; nuclear envelope begins to disintegrate. |
Prometaphase | Nuclear envelope fragments; spindle fibers attach to kinetochores; chromosomes begin moving. |
Metaphase | Chromosomes align at metaphase plate; spindle fibers fully attached. |
Anaphase | Sister chromatids separate and move to opposite poles. |
Telophase | Nuclear envelopes reform; chromosomes decondense; spindle apparatus disassembles. |
Cytokinesis | Cytoplasm divides, forming two daughter cells. |
Definitions of Key Terms
Chromatid: One of two identical halves of a duplicated chromosome.
Centromere: The region of a chromosome where the two sister chromatids are joined and where spindle fibers attach during mitosis.
Spindle Apparatus: A structure made of microtubules that segregates chromosomes during mitosis.
Kinetochores: Protein complexes on the centromere where spindle fibers attach.
Example: Mitosis in Animal Cells
In a typical animal cell, mitosis ensures that each daughter cell receives an identical set of chromosomes.
For example, a human somatic cell with 46 chromosomes will produce two daughter cells, each with 46 chromosomes after mitosis and cytokinesis.
Additional info:
Some cells, such as neurons, may remain in G0 permanently and do not divide.
Errors in mitosis can lead to aneuploidy, a condition where cells have an abnormal number of chromosomes.
