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Let's begin with what is cell cycle. Cell cycle is the controlled tightly
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regulated sequence of events that occurs between one cell division and the next
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It consists of four main stages G1 phase or CAP1 phase, S phase or synthesis
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phase, G2 phase or CAP2 phase, M phase or mitosis. G1, S and G2 together called as
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the interphase. Now let us see the major events in each stage. G1 phase or CAP1
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phase is a preparatory phase for DNA synthesis. The cell increases in size and
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synthesizes proteins necessary for DNA replication. Cellar contents are duplicated, synthesizes many proteins, lipids and organelles like ribosomes and
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mitochondria except chromosomes. The cell accumulates energy reserves and building blocks for DNA synthesis. The cell assesses environmental conditions to
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ensure that they are favorable for division. The next phase is the S phase
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or in this phase synthesis of DNA occurs. DNA replication occurs in this phase
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resulting in the formation of two identical copies of each chromosome known as sister chromatids as you see here. This process ensures that each
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daughter cell will receive an exact copy of the genetic material. Centrosome duplication also takes place during this phase. The centrosome is
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essential for organizing the mitotic spindle. It is also duplicated during S
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phase and this sets the stage for proper chromosome segregation during mitosis. The
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production of histone proteins occurs to package the newly synthesized DNA into
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chromatin also takes place in this phase ensuring that the DNA is organized and
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compacted properly. Overall gene expression and protein synthesis are low in S phase. The exception is regarding the histones
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which are synthesized during S phase for DNA packaging. The chromatin remains in a semi-condensed state allowing for the DNA
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replication process to occur. The cell continuously monitors the integrity of the DNA. The next phase is a G2 phase or captive phase. It is a preparatory phase
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for mitosis. The cell continues to grow and produces proteins and lipids
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required for mitosis. Significant amount of proteins required for chromosome movement and cell division are produced. This includes proteins that makes
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mitotic spindle. Microtubules begin to reorganize to form the spindle apparatus that will be used to separate the sister chromatids during mitosis as you see
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here. Organelles are duplicated and the cytoskeleton is reorganized to prepare for cell division. The cell checks for DNA damage and ensures that all DNA has
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been accurately replicated before entering mitosis. If any damage is detected the cell may either repair the DNA or trigger apoptosis or program cell
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death if the damage is irreparable. Now the cell enters mitosis. So we have
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already discussed the stages of mitosis. Please watch the video for more. Mitosis
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simply divided into prophase, metaphase, anaphase and telophase where the replicated chromosomes are separated. It's a type of division that results in
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two genetically identical daughter cells each with the same number of chromosomes
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as the parent cell and this is followed by cytokinesis that resulting in the
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separation or physical separation of the cytoplasm and the formation of two
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identical daughter cells. Then each daughter cell then enters the g1 phase
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of a new cell cycle. This process is essential for growth development and
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tissue repair in multicellular organisms. Hope you are clear with the stages and
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major features that is happening in each of the stages of cell cycle. Take care
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Stay blessed. Thank you so much. You are with biologyexams4u.com
