Cell Cycle
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- Опубліковано 8 вер 2024
- The cell cycle is the sequence of events that occurs leading up to and during somatic cell division. There are two main parts of the cell cycle: interphase (during which a cell prepares to divide) and the mitotic phase (during which division occurs).
Interphase itself consists of three main subphases: G1, S, and G2.
During G1, the cell becomes highly active, preparing for division by duplicating many of its organelles and synthesizing proteins.
In the S phase, the cell replicates its DNA, so there are two complete copies available.
The final part of interphase is G2, during which the cell continues to increase in size and produce further proteins necessary for division.
After G2, the cell enters the second part of the cell cycle: the mitotic phase. The mitotic phase consists of two processes, mitosis (the division of the nucleus) and cytokinesis (the division of the cytoplasm).
Mitosis has four stages: prophase, metaphase, anaphase, and telophase.
By the end of mitosis, the DNA that was duplicated in the S phase of interphase has been separated into two identical sets, each within its own nucleus.
Cytokinesis is the division of the cytoplasm to form two separate cells. Occurring at the same time as the final phases of mitosis, a contractile ring develops and deepens to divide the cell in two. Therefore, at the end of the mitotic stage, one cell has divided to form two daughter cells, each with a complete set of DNA.
After dividing, the daughter cell re-enter G1. Each cell may then prepare to divide again, or pause, in which case, it is referred to as being in G0, or the quiescent phase.
A cell may remain in G0 indefinitely, or later return to complete G1.
INTERPHASE
Interphase is the longest phase in the cell cycle, accounting for DNA replication, production of additional organelles, and cytosol and cell growth.
During this time, the cell contains a tangled mass of chromatin within a fully formed nuclear envelope.
Interphase is subdivided into four phases: G0, G1, S phase, and G2. S denotes synthesis and refers to DNA replication, and G denotes gaps when no DNA replication is occurring.
G0 phase
Some cells enter a quiescent, non-dividing state after mitosis, where the cell cycle is suspended, and they do not enter G1. This is known as the G0 phase and is common in fully differentiated cells, such as skeletal muscle cells and neurons.
G1 phase
The G1 phase, also known as gap 1 (or growth phase 1), can range between 8 and 10 hours. The cell is highly metabolically active during G1, with the following cellular activities taking place:
Replication of organelles.
Synthesis of cytosolic components (e.g., enzymes required during the S phase).
Beginning of centrosome replication.
S phase
The S phase, also known as the synthesis phase, lasts about 8 hours, during which DNA replication occurs, ensuring that the two daughter cells produced acquire equal and identical sets of chromosomes.
G2 phase
The G2 phase, also known as gap 2, lasts about 4-6 hours, during which the following occurs:
Replication of organelles completed.
Synthesis of cytosolic components completed.
Centrosome replication completed.
Protein synthesis.
Energy production for cell division.
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