Chapter 5: Mitosis is the Basis of Asexual Reproduction Section 5.1: The Cell Cycle and Mitosis Living things must be able to reproduce. For unicellular organisms, cell reproduction is necessary to maintain the continuity of the species (asexual reproduction). For multicellular organisms, cell reproduction is necessary for growth of the individual and replacement of worn out cells. Did you know? We shed millions of skin cells per hour. We completely replace our outer layer or epidermis of our skin every 15-30 days. Our bodies make approximately 300 000 000 new cells a minute. Cells in your body divide at different speeds or rates (bottom of p. 138), but you will always be making cells throughout your life... - replace damaged or diseased cells - new linings for airways, stomach, intestines every couple of weeks. Before a cell reproduces, the cell must replicate all the organelles within it, including the nucleus. The DNA within the nucleus must be duplicated so that daughter cells will contain identical information as the parent cell. Mitosis is a process that divides the duplicated DNA into two equal parts. Cytokinesis is a process that separates the cell contents into two daughter cells. There are specific conditions that must be met as the cell proceeds through the cell cycle and prepares to divide Dec 8 8:35 PM 1
The Cell Cycle Three Stages Interphase Mitosis Cytokinesis Interphase: - longest of the 3 stages - it is the stage in which the cell is carrying out the functions necessary for survival and cells that divide prepare for reproduction During interphase the cell will increase in size and make the proteins and molecules necessary for the cell to function. Some organelles (such as mitochondria and chloroplasts) begin to duplicate. The cell's DNA is also copied. After the DNA is copied the cell continues to grow and make proteins for the new cells that will be formed after cytokinesis. Mitosis: - shortest stage - the process of cell division that results in the growth and/or cell replacement of all cells of the body, with the exception of egg and sperm cells (These are produced by meiosis.) - During this process the contents of a cell's nucleus divide. - The division results in two daughter nuclei, each with the same number and kinds of chromosomes as the original cell. Each daughter cell will have half the cytoplasm and newly created organelles. Dec 8 9:18 PM 2
4 Phases of Mitosis Prophase Metaphase Anaphase Telophase Prophase: - The double stranded x-shaped chromosomes shorten and thicken. - The nuclear membrane begins to fade. Metaphase: - X-chromosomes, which are attached to fibers, are pulled into a single line across the middle of the cell. Anaphase: - The fibers shorten and pull the strands of each chromosome apart. The two strands of each chromosome move to opposite poles. Dec 8 8:19 PM 3
Telophase: - Two sets of of single-stranded chromosomes are at opposite poles and a nuclear membrane begins to form around each set of chromosomes. Cytokinesis: - final stage - Cytokinesis separates the 2 nuclei into two daughter cells. - In animal cells, the cell membrane pinches together to divide the cell's cytoplasm and organelles. - In plant cells, a cell plate forms along the center of the cell to divide the cell into two daughter cells. Dec 12 5:16 PM 4
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