1 PowerPoint to accompany CONCEPTS IN BIOLOGY ELEVENTH EDITION Enger Ross CHAPTER 8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 8.1 MITOSIS Cell division is essential to: Cell division is essential to: Replace dead cells (50 million Replace dead cells (50 million cells die per second) cells die per second) Repair damaged tissues Repair damaged tissues Growth Growth Maintain the body Maintain the body After a mitotic cell division, information about the cell is equally distributed to daughter cells. After a mitotic cell division, information about the cell is equally distributed to daughter cells.

3 8.2 THE CELL CYCLE All cells go through almost the same cell cycle. All cells go through almost the same cell cycle. Even though we divide cell division into 5 stages, once cell division starts it is a continuous process. Even though we divide cell division into 5 stages, once cell division starts it is a continuous process. The five stages in cell division are: The five stages in cell division are: 1. G 1 — gap (growth) phase one 2. S — synthesis 3. G 2 — gap (growth) phase two 4. Cell division (mitosis and cytokinesis) 5. G 0 — gap (growth) mitotic dormancy

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5 THE CELL CYCLE During the G 0 phase, cells are not in the cell division cycle, they are differentiated or specialized in their function. During the G 0 phase, cells are not in the cell division cycle, they are differentiated or specialized in their function. Some cells remain in the G 0 phase (e.g., nerve cells) and others get back to the cell cycle (G 1, S, and G 2, e.g., bone cells). Some cells remain in the G 0 phase (e.g., nerve cells) and others get back to the cell cycle (G 1, S, and G 2, e.g., bone cells). The three phases G 1, S, and G 2, occur during the stage called interphase. The three phases G 1, S, and G 2, occur during the stage called interphase.

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7 THE CELL CYCLE During G 1 phase cell growth, manufacture of tRNA, rRNA, enzymes cell components and enzymes are made. During G 1 phase cell growth, manufacture of tRNA, rRNA, enzymes cell components and enzymes are made. DNA synthesis occurs during the S stage. DNA synthesis occurs during the S stage. Proteins required for the spindles are synthesized in the G 2 stage. During G 2 phase the cell prepares Proteins required for the spindles are synthesized in the G 2 stage. During G 2 phase the cell prepares to go through mitosis. to go through mitosis. At interphase, cells are engaged in their metabolic activities such as photosynthesis, muscle cell contractions, and glandular-cell secretion. At interphase, cells are engaged in their metabolic activities such as photosynthesis, muscle cell contractions, and glandular-cell secretion.

8 8.3 STAGES OF MITOSIS The stages of mitosis are: The stages of mitosis are: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

9 PROPHASE Prophase; this is the first stage of mitosis and at this stage : Prophase; this is the first stage of mitosis and at this stage : Individual chromosomes become visible. Individual chromosomes become visible. Nuclear membrane begins to disappear. Nuclear membrane begins to disappear. Spindles begin to form. Spindles begin to form. The two identical chromatids are attached to the centromere. The two identical chromatids are attached to the centromere. Centrioles move to opposite poles. Centrioles move to opposite poles.

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13METAPHASE Metaphase; is the second stage of mitosis, and at this stage: Metaphase; is the second stage of mitosis, and at this stage: The nuclear membrane has disappeared. The nuclear membrane has disappeared. Centrioles are at opposite poles. Centrioles are at opposite poles. Chromosomes are aligned at equatorial plane. Chromosomes are aligned at equatorial plane. Each chromosome still has two chromatids. Each chromosome still has two chromatids. In human cells there are 46 chromosomes, (each with two chromatids) or 92 chromatids. In human cells there are 46 chromosomes, (each with two chromatids) or 92 chromatids. Chromosomes are attached to the spindle. Chromosomes are attached to the spindle.

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16 ANAPHASE Anaphase is the third stage of mitosis and at this stage: Anaphase is the third stage of mitosis and at this stage: Centromeres split and chromatids separate. Centromeres split and chromatids separate. Chromatids are also called daughter chromosomes. Chromatids are also called daughter chromosomes. Chromatids move to opposite poles by a motor protein (kinetochore). Chromatids move to opposite poles by a motor protein (kinetochore). Each chromatid moving to the opposite pole is the exact copy of the other. Each chromatid moving to the opposite pole is the exact copy of the other.

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18 TELOPHASE Telophase is the last stage of mitosis and at this stage: Telophase is the last stage of mitosis and at this stage: Cytokinesis or equal division of the cell cytoplasm takes place. Cytokinesis or equal division of the cell cytoplasm takes place. Each set of chromosomes unwinds. Each set of chromosomes unwinds. Nuclear membrane reappears and chromosomes are enclosed in it. Nuclear membrane reappears and chromosomes are enclosed in it. Nucleoli of the cell reappears. Nucleoli of the cell reappears. Each of the daughter cells formed now enter G 1 stage of interphase. Each of the daughter cells formed now enter G 1 stage of interphase. The cells grow and enter another cycle of mitosis. The cells grow and enter another cycle of mitosis.

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PLANT AND ANIMAL CELL DIFFERENCES For the most part, animal and plant cells have very similar cell division cycles. For the most part, animal and plant cells have very similar cell division cycles. Among the differences are: Among the differences are: Plant cells do not have centrioles, but somehow are able to produce a spindle. Plant cells do not have centrioles, but somehow are able to produce a spindle. There is a difference in the process of cytokinesis, in animal cells form a cleavage furrow and in plants a cell plate is formed. There is a difference in the process of cytokinesis, in animal cells form a cleavage furrow and in plants a cell plate is formed.

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DIFFERENTIATION Even though all cells originate from a set of genes from your father in his sperm, and a set of genes from your mother in her egg, they are all the same genes in your body except for mutations. Even though all cells originate from a set of genes from your father in his sperm, and a set of genes from your mother in her egg, they are all the same genes in your body except for mutations. All cells in the body are genetically identical but have different functions, e.g., nerve cells, muscle cells, red blood cells... each with a specific function. All cells in the body are genetically identical but have different functions, e.g., nerve cells, muscle cells, red blood cells... each with a specific function. The process of creating these specialized cells is called cell differentiation. The process of creating these specialized cells is called cell differentiation.

26 STEM CELLS Stem cells are cells that can become any cell type. Stem cells are cells that can become any cell type. Stem cells found in the bone marrow can be differentiated and become any cell e.g., red blood cells, nerve cells... Stem cells found in the bone marrow can be differentiated and become any cell e.g., red blood cells, nerve cells... The reason that bone marrow transplants are used to cure certain diseases is because the stem cells can differentiate to obtain the desired cells. The reason that bone marrow transplants are used to cure certain diseases is because the stem cells can differentiate to obtain the desired cells.

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