MITOSIS, CYTOKINESIS, AND THE CELL CYCLE

The only way to create a new cell is to duplicate a pre-existing one. The original cell is called the parent cell, and the two new cells, which are genetically identical, are called daughter cells. The series of steps leading to and involving the duplication of a cell is called the cell cycle. The cell cycle involves cell growth, chromosome replication, chromosome segregation, and cell division, which take place over the course of the four sequential phases of the cell cycle: G1, S, G2, and M. The first three phases are together called interphase.
Taking place between G1 and G2, S phase is when DNA replicates and chromosomes duplicate. It is critical that this replication is accurate, and that every nucleotide is copied exactly once.
Mitosis has 5 stages: prophase, prometaphase, metaphase, anaphase, and telophase.
During prophase, chromosomes condense within the nucleus, with each chromosome consisting of two linked sister chromatids. Outside the nucleus, the mitotic spindle assembles between two centrosomes. Next we have prometaphase, which begins when the nuclear envelope breaks down. This means that chromosomes can now attach to spindle microtubules. This occurs via kinetochores and results in the movement of the chromosomes. Metaphase involves the alignment of chromosomes along the equator of the spindle, with microtubules attaching sister chromatids to opposite poles of the spindle. Anaphase involves the synchronized separation of sister chromatids to form two daughter chromosomes, which are pulled towards the spindle poles. During this process, not only do the kinetochore microtubules shorten, but the spindle poles also move apart. Telophase is the last stage of mitosis. At this point, the two sets of daughter chromosomes arrive at the spindle poles and decondense. The Initiationformation of the two nuclei, which occurs when a nuclear envelope assembles around the two genomes, means that mitosis is over.
Cytokinesis, which is the division of the cytoplasm, occurs during mitosis. It occurs thanks to the formation of a contractile ring of actin and myosin filaments, which form a rapidly deepening furrow. The contractile ring begins to assemble during anaphase, just beneath the plasma membrane. As the ring contracts, there is formation of an intercellular bridge and fusion of intracellular vesicles to add more plasma membrane to compensate for the extra surface area. At the center of the intercellular bridge, there is what is called the midbody, which consists of the remains of the interdigitated interpolar microtubules at the spindle midzone, which are packed together within a dense matrix material. Abscission is the final cleaving of the two daughter cells. So cytokinesis has 4 steps: initiation, contraction, membrane insertion, and completion.

Cell Cycle Regulation:
   • Cyclins and CDKs Cell Cycle Regulation  

Cytoskeleton:
   • THE CYTOSKELETON - MICROTUBULES, INTERMEDI...