Mitosis.pdf

THE CELL DIVISION CELL DIVISION (Cell Reproduction) Raiyed M. Adeel 02/10/2018  You are made of many different types of cells. Nerve cells, skin cells, muscle cells, and many more. These cells obviously have many different functions, yet they all develop from the first cell...

THE CELL DIVISION CELL DIVISION (Cell Reproduction) Raiyed M. Adeel 02/10/2018  You are made of many different types of cells. Nerve cells, skin cells, muscle cells, and many more. These cells obviously have many different functions, yet they all develop from the first cell that makes you. So do they all have the same DNA? Are all the cells in your body genetically identical? How does the first cell of an organism know to become two cells, then four cells, and so on? What tells these cells what to do? Your body produces about 25 million genetically identical cells every second. Raiyed M. Adeel 02/10/2018  These new cells are formed when older cells divide, a process called cell division or cell reproduction. Cell division is the final step in the life of a cell, otherwise known as the cell cycle. Eukaryotic cells and prokaryotic cells complete this process by a number of different mechanisms. The cell cycle is a repeating series of events, during which the eukaryotic cell carries out its necessary functions, including metabolism, cellular growth, and division, resulting in two genetically identical daughter cells. Raiyed M. Adeel 02/10/2018 CELL DIVISION IN EUKARYOTES Cell division in eukaryotic organisms is very different from that in prokaryotes, mainly because of the many chromosomes in the nuclei of eukaryotic cells. Cell division in eukaryotic organisms is necessary for development, growth, and repair. This cell division ensures that each resulting daughter cell receives a complete copy of the organism’s entire genome. Remember that all of an organism’s DNA must be present in each somatic, or body, cell. Raiyed M. Adeel 02/10/2018  The formation of gametes, an organism’s reproductive cells, such as sperm and egg cells, involves a completely different method of cell division. This cell division ensures that each gamete receives half the amount of an organism’s DNA. Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018  THE CELL CYCLE The life of a eukaryotic cell is a cycle, known as the cell cycle. The cell cycle is a repeating series of cellular growth and division. The cell cycle has five phases: the first growth (G1) phase, the synthesis (S) phase, the second growth (G2) phase, mitosis, and cytokinesis, though many consider mitosis and cytokinesis to be combined into one phase. The cell spends the majority of the cycle in the first three phases of the cycle, collectively known as interphase. Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018 MITOSIS Huiam Salih Alaraby 11  Mitosis Mitosis is the division of the cell’s nucleus, the final step before two daughter cells are produced. The cell enters mitosis as it approaches its size limitations. Four distinct phases of mitosis have been recognized: prophase, metaphase, anaphase, and telophase, with each phase merging into the next one. Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018  PROPHASE Prophase is the first and longest phase of mitosis. During prophase, the DNA coils up into visible chromosomes, each made up of two sister chromatids held together by the centromere. The nucleus disappears as the nuclear envelope and nucleolus break apart. The centrioles begin to move to opposite ends, or poles, of the cell. As the centrioles migrate, the fiber-like spindle begins to elongate between the centrioles. The spindle is a thin, cage-like structure made out of microtubules. Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018  METAPHASE During metaphase the spindle attaches to the centromere of each chromosome. Helped by the spindle, the chromosomes line up at the center, or equator, of the cell, also known as the metaphase plate. Each sister chromatid is attached to a separate spindle fiber, with one fiber extending to one pole, and the other fiber extending to the other pole. This ensures that the sister chromatids separate and end up in distinct cells after cell division Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018  ANAPHASE Anaphase is the phase in which the sister chromatids separate. The sister chromatids are pulled apart by the shortening of the microtubules of the spindles, similar to the reeling in of a fish by the shortening of the fishing line. One sister chromatid moves to one pole of the cell, and the other sister chromatid moves to the opposite pole. At the end of anaphase, each pole of the cell has a complete set of chromosomes, identical to the amount of DNA at the beginning of G1 of the cell cycle. Raiyed M. Adeel 02/10/2018  TELOPHASE Telophase is essentially the opposite of prophase. The chromosomes begin to unwind in preparation to direct the cell’s metabolic activities. The spindle begins to break down, allowing a new nucleus to form. This is followed by cytokinesis, the division of the cytoplasm, resulting in two genetically identical cells, ready to enter G1 of the next cell cycle. Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018  CYTOKINESIS Cytokinesis differs between plant and animal cells. In animal cells, the plasma membrane pinches inward along the cell’s equator until two cells are formed. In plant cells, a cell plate forms along the cells equator. A new membrane grows along each side of the cell plate, with a new cell wall forming on the outside of each new membrane. Raiyed M. Adeel 02/10/2018 25 Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018 Prophase Metaphase Anaphase Telophase Raiyed M. Adeel 02/10/2018 Raiyed M. Adeel 02/10/2018  THANK YOU Cell Division is