Question

Explain the different Cell Cycle stages and what event occurs with each one.

Answer 1

The cell cycle is divided into two main stages: the interphase or nondividing stage and the mitotic or dividing stage. In interphase is the stage where a cell prepares itself by replicating its own genetic information and all of its organelles. The cell goes through this period of growth before it undergoes mitosis. The following are its three important phases. Gap 1 (G1) phase in the first gap, the cell increases in size preparation for division. During this stage, the cell prepares itself for DNA synthesis. Synthesis (S) phase DNA synthesis (replication) occurs. Chromosomes are also replicated which later on will become sister chromatids. Gap 2 (G2) phase this is the second gap. The cell continues to grow and synthesize RNA and proteins. There is also a G2 checkpoint to see if the cell is already prepared for mitosis. Some cells undergo the cell cycle only once, or they stop dividing. These cells will go to the Gap 0 (G0) phase, the resting phase of the cell. Nerve and blood cells remain in G0 phase for the rest of their lives. Thus, nerve cells and blood cells do not undergo mitosis. In mitosis once the cell is ready for cell division it will go to the next stage- mitosis. Mitosis is the process of nuclear division of a cell. Prophase is the of mitosis that takes up around 50-60 percent of total time for mitosis. It is subdivided into three substages: early, middle, and late prophase. In early prophase, chromosomes condense and start to coil up into short rods, the nuclear membrane disappers, and the centrioles appear and move toward the opposite sides (the poles) of the nuclues. In the middle prophase, mitotic spindle fibers are formed between the centrioles.Asters also formed on each side of the nucleus. The centrioles move towrdsthe poles. The nuclear membrane dissolves. In late prophase, chromosomes are attached to the centrioles through the spindle fibers. In metaphase, the centrioles have completed their migration toward the poles. The double-stranded chromosomes are aligned at the cells's midplane (equator). The centromeres of each chromosome are attached to the fully formed spindle fibers. In anaphase, the centromeres, followed by the chromatids, are separated when the spindle fibers shorten and pull the chromatids toward the end of the poles. The chromatids are now called chromosomes. Telophase is the last stage of mitosis which is usually referred to as the "reveres prophase"  stage.In this stage, the spindle fibers disappear, the nuclear membrane and nucleoli reappear, and the chromosomes uncoil. Cytokinesis, follows mitosis. In animal cells, a cleavage furrow is formed until the membrane separates, forming two daughter cells. In plant cells, a cell plate is created that eventually develops into a cell wall.