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Transcript
Cell Division Many cells in your body are growing and dividing right now! Cell Cycle – the regular sequence of growth and division that cells undergo During the cell cycle, a cell grows, prepares for division, and divides into two new cells, which are called “daughter cells”. Each daughter cell then begins the cell cycle again! The first stage of the cell cycle is called interphase Interphase – the cell grows, makes a copy of its DNA, and prepares to divide into two cells STAGE 1: INTERPHASE Growing – the cell grows to its full size and produce structures it needs – the cell makes new ribosomes and produces enzymes, etc Copying DNA – the cell makes an exact copy of the DNA in its nucleus in a process called replication o Replication of DNA is very important since each daughter cell must have a complete set of DNA to survive – at the end of DNA replication, the cell contains two identical sets of DNA Preparing for Division – the cell produces structures that it will use to divide into two new cells – at the end of interphase, the cell is ready to divide! Mitosis – is the stage of cell division where the cell’s nucleus divides into two nuclei During mitosis, one copy of the DNA is distributed into each new daughter cell Turn to page 97 of your textbook and look at figure 20. Chromosomes – a double rod of condensed chromatin Each identical rod in a chromosome is called a chromatid and the two chromatids are held together by a structure called a centromere STAGE 2: MITOSIS 2A: Prophase – o Chromatin in the nucleus condenses to form chromosomes o Pairs of centrioles move to opposite sides of the nucleus o Spindle fibers form a bridge between the ends of the cell o The nuclear envelope breaks down 2B: Metaphase – o The chromosomes line up across the center of the cell o Each chromosome attaches to a spindle fiber at its centromeres 2C: Anaphase – o The centromeres split and the two chromatids separate and each chromatid becomes a new chromosome o The new chromosomes move to opposite ends of the cells o The cell stretches out as the opposite ends are pushed apart 2D: Telophase – o The chromosomes begin to stretch out and lose their rod-like appearance and a new nuclear envelope forms around each region of chromosomes STAGE 3: CYTOKINESIS During cytokinesis the cytoplasm divides and the organelles are distributed into each of the new cells – cytokinesis usually begins the same time as Telophase When cytokinesis is complete, two new daughter cells have formed Each daughter cell has the same number of chromosomes as the original parent – at the end of cytokinesis, each cell enters interphase and the cell cycle begins again!! Cytokinesis in Animal Cells – the cell membrane squeezes together around the middle of the cell and the cytoplasm pinches into two new cells, with about half the organelles Cytokinesis in Plant Cells – the cell wall can’t squeeze together so the cell develops a cell plate that forms across the middle of the cell