MITOSIS (CELL CYCLE AND CELL DIVISION)

• The continuity of life from one cell to another has its foundation in the reproduction of cell by way of the cell cycle.
• The science that study cells is Cytology.
• Cytology is a branch of science that deals with the structures and function of cells.
• The growth of multicellular organisms is not only due to increase in the size of cells but it also involves increase in the number of cellular units.
• Cell division accomplishes the increase in the number of cells in an organism.
• Cell divides to give rise to new ones, to replace those old and injured cells and to promote growth of organisms.
• During development from stem to fully differentiated, cells in the body alternately divide (mitosis) and "appear" to be resting (interphase).
• The sequence of activities exhibited by cell is called cell cycle.
• Cell cycle is an orderly sequence of events that describes the stages of a cell's life from the division of a single parent cell to the production of two new cells daughter cells.
• The mechanism involved in the cell cycle are highly regulated and involves two major types: Mitosis and Meiosis.
• Our cell has checkpoints before it will undergo cell division.
• Checkpoint is a critical point in the cell cycle where to "stop" and "go-ahead" signals that regulate the cell cycle.
• The major checkpoints in mitosis are found in the G1,G2, and M phase of the cell cycle.
• Some checkpoints are found in interphase. On this phase, cells may appear inactive but they are quite the opposite.
• Interphase is the longest of the complete period of the complete cell cycle during which DNA replicates, the centrioles divide, and proteins are actively produced.
• By studying molecular events in cells, scientist have determined that interphase can be divided into 4 steps: GAP 1 (G1), S (Synthesis), and GAP 2 (G2).
• GAP 0 phase are times when a cell will leave the cycle and quit dividing. It means that if the cell does not receive "go-ahead" signal, it will exit the cell cycle and switch to a non-dividing stage which is the Gap 0.
• Gap 0 phase may be temporary resting period or more permanent. An example of this is the neuron in the brain, it is cell that has reached an end stage of development and will no longer divide.
• Gap 1 phase also known as restriction point.
• In g1 phase, cell increase in size, produce RNA and synthesize protein.
• An important cell cycle control mechanism activated during this period; it ensures that everything is ready for DNA synthesis.
• The G1 checkpoint ensures that the cell is large enough to divide and that enough nutrients are available to support the resulting daughter cells and most importantly it ensures that DNA is ready for synthesis.
• Synthesis phase or S phase that produce two similar daughter cells, the complete DNA instructions in the cell must be duplicated. DNA replication occurs during this phase.
• GAP 2, on this phase the gap between DNA synthesis and mitosis, the cell will continue to grow and produce new proteins.
• GAP 2 checkpoint ensures that DNA replication in S phase has been successfully completed.
• The S phase is a checkpoint that determines if the cell can now proceed to enter mitotic division (mitosis).
• For Gap 0 when the cell does not receive "go-ahead" signal, it will exit the cell cycle and switch to a non-dividing stage which is called Gap 0.
• For Gap 1, produce RNA, synthesizes and ensure that everything is ready for DNA synthesis.
• Gap 2 where cell continue to grow and produce new proteins.
• Mitosis is the part of cell cycle that results in identical daughter nuclei that are also genetically identical to the original parent nucleus.
• In mitosis, both parent and daughter nuclei are same ploidy level-diploid (2N) for most plant and animals. It also occurs in a series of sequential stages in the cell, especially in the nucleus.
• Nuclear division also known karyokinesis is a continuous but it is conveniently divided into four different stages, namely: prophase, metaphase, anaphase, and telophase.
• Prophase is marked by the condensation of chromosome to form visibly distinct chromosomes.
• The chromosomes is made up of two sister chromatids joined together at the centromere.
• Chromosomes are structures within the nucleus that are made up of DNA, the genetic material of an organisms.
• As prophase progresses, the chromosomes become shorter and thicker as result of intricate coiling.
• In the late, prophase, the nuclear membrane disintegrates, the nucleolus disappears and mitotic spindle forms.
• Metaphase, in this phase, chromosomes are aligned in a plane called metaphase plate, or the equatorial plate.
• The significant event occurred in metaphase stage is alignment of chromosomes at the middle in the plane called metaphase plate.
• Anaphase is the stage where the centromeres divide and the two sister chromatids move toward the opposite poles of the spindle.