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Limits to Cell Growth • There Are Two Reasons Why the Cell Divides: 1. The 9/29/08 Interest Grabber Section Outline Section 10-1 Section 10-1 Getting Through Materials move through cells by diffusion. Oxygen and food move into 10–1 Cell Growth cells, while waste products move out of cells. How does the size of a cell A. Limits to Cell Growth affect how efficiently materials get to all parts of a cell? 1. DNA “Overload” Work with a partner to complete this activity. 2. Exchanging Materials 3. Ratio of Surface Area to Volume 1. On a sheet of paper, make a drawing of a cell that has the following dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell 4. Cell Division about one half the size of your cell on a separate sheet of paper. 2. Compare your drawings. How much longer do you think it would take to get from the cell membrane to the center of the big cell than from the cell membrane to the center of the smaller cell? 3. What is the advantage of cells being small? Go to Go to Section: Section: Limits to Cell Growth DNA “Overload” • DNA contains all the information to control the cell. • There are two reasons why the cell divides: • There is only a certain amount of DNA within a cell. • As the cell gets larger, there are more demands on the 1. The larger the cell, the more demands the cell DNA and it won’t be able to keep up. places on its DNA. 2. The cell has trouble moving enough nutrients and wastes across the cell membrane. Go to Go to Section: Section: Exchanging Materials Ratio of Surface Area to Volume • Materials such as food, oxygen, water and wastes, • As the cell grows, its volume grows much more rapidly enter and leave the cell through the cell membrane. than its surface area. • Some things pass through by diffusion, but other must • Take a look at the chart to understand. use the protein channels or pumps. • Only a certain amount can pass through within a given time. As the cells gets larger, more and more materials are going to have to pass through the membrane which may become too much for the channels. Go to Go to Section: Section: 1 9/29/08 Ratio of Surface Area to Volume in Cells Interest Grabber Section 10-1 Section 10-2 Cell Cycle Cell Size The cell cycle represents recurring events that take place in the period of time from the beginning of one cell division to the beginning of the next. In addition to cell division, the cell cycle includes periods when the cell is growing and actively producing materials it needs for the next division. Surface Area (length x width x 1. Why is the cell cycle called a cycle? 6) Volume (length x width x height) 2. Why do you think that it is important for a cell to grow in size during its Ratio of Surface Area cell cycle? to Volume 3. What might happen to a cell if all events leading up to cell division took place as they should, but the cell did not divide? Go to Go to Section: Section: Section Outline Section 10-2 Chromosomes 10–2 Cell Division • Chromosomes carry the information that is passed on from one A. Chromosomes generation to the next. B. The Cell Cycle • They are made up of DNA and proteins. C. Events of the Cell Cycle • Every organism has a specific number of chromosomes in each cell. D. Mitosis 1. Prophase – Fruit flies have 8 2. Metaphase – Humans have 46 3. Anaphase – Carrots have 18 4. Telophase • Chromosomes are only visible E. Cytokinesis during cell division. • DNA is copied just before cell division. • They consist of two sister chromatids. Go to Go to Section: Section: Figure 10–4 The Cell Cycle Section 10-2 Three Stages of the Cell Cycle Introductions 1. Interphase 2. Mitosis 3. Cytokinesis • What is the Cell Cycle? G1 phase – Cell reproduction in which two identical cells are made from one cell • Why do cells need to reproduce? M phase – So organisms can grow and replace old, worn out cells • What types of cells reproduce using mitosis? S phase – Body cells - Any cells except the sex cells. G2 phase Go to Go to Section: Section: 2 9/29/08 Interphase Mitosis • G1 phase: – Cell grows in size. • Scientists divide the events of mitosis into four phases: – Cell synthesizes new proteins – Prophase and organelles. – Metaphase • S phase: – Anaphase – DNA is replicated. – Telophase • G2 phase: – Organelles and molecules for cell division are produced. – Cell grows a little more. Go to Go to Section: Section: Prophase Metaphase • DNA coils to form chromosomes. • Nuclear membrane and nucleolus disappear. • Chromosomes are moved to the • Centrioles move to opposite side middle of the cell by the of the cell. microtubules of the spindle. • Spindle fibers begin to develop. Go to Go to Section: Section: Anaphase Telophase • Centromeres split. • Sister chromatids move • Chromosomes begin to apart to opposite side of the uncoil. cell becoming individual • Nuclear membrane and chromosomes. nucleolus reappear. • Spindle fibers and centrioles begin to disappear. • Cytoplasm begins to pinch inward. Go to Go to Section: Section: 3 9/29/08 Figure 10–5 Mitosis and Cytokinesis Section 10-2 Cytokinesis Spindle forming Centrioles • In animals, the cytoplasm pinches in the middle until it Nuclear Chromatin Centromere Centriole becomes two equal parts. Chromosomes envelope (paired chromatids) • In plants, a cell plate forms Interphase Prophase Spindle half way between the two nuclei. It continues to go Cytokinesis Centriole until the cell is split. Individual Metaphase Telophase chromosomes Nuclear Anaphase envelope reforming Go to Go to Section: Section: Figure 10–5 Mitosis and Cytokinesis Figure 10–5 Mitosis and Cytokinesis Section 10-2 Section 10-2 Spindle Spindle forming forming Centrioles Centrioles Nuclear Chromatin Centromere Centriole Nuclear Chromatin Centromere Centriole Chromosomes Chromosomes envelope envelope (paired chromatids) (paired chromatids) Interphase Interphase Prophase Spindle Prophase Spindle Cytokinesis Centriole Cytokinesis Centriole Individual Metaphase Individual Metaphase Telophase chromosomes Telophase chromosomes Nuclear Anaphase Nuclear Anaphase envelope envelope reforming reforming Go to Go to Section: Section: Figure 10–5 Mitosis and Cytokinesis Figure 10–5 Mitosis and Cytokinesis Section 10-2 Section 10-2 Spindle Spindle forming forming Centrioles Centrioles Nuclear Chromatin Centromere Centriole Nuclear Chromatin Centromere Centriole Chromosomes Chromosomes envelope envelope (paired chromatids) (paired chromatids) Interphase Interphase Prophase Spindle Prophase Spindle Cytokinesis Centriole Cytokinesis Centriole Individual Metaphase Individual Metaphase Telophase chromosomes Telophase chromosomes Nuclear Anaphase Nuclear Anaphase envelope envelope reforming reforming Go to Go to Section: Section: 4 9/29/08 Figure 10–5 Mitosis and Cytokinesis Concept Map Section 10-2 Section 10-2 Spindle forming Cell Cycle Centrioles includes Nuclear Chromatin Centromere Centriole Chromosomes envelope (paired chromatids) Interphase Prophase Spindle Interphase M phase (Mitosis) Cytokinesis Cytokinesis Centriole Individual Metaphase is divided into is divided into Telophase chromosomes Nuclear Anaphase envelope reforming G1 phase S phase G2 phase Prophase Metaphase Anaphase Telophase Go to Go to Section: Section: Interest Grabber Section Outline Section 10-3 Section 10-3 Knowing When to Stop 10–3 Regulating the Cell Cycle Suppose you had a paper cut on your finger. Although the cut may have A. Controls on Cell Division bled and stung a little, after a few days, it will have disappeared, and your B. Cell Cycle Regulators finger would be as good as new. 1. Internal Regulators 2. External Regulators 1. How do you think the body repairs an injury, such as a cut on a C. Uncontrolled Cell Growth finger? 2. How long do you think this repair process continues? 3. What do you think causes the cells to stop the repair process? Go to Go to Section: Section: Control of Cell Division Section 10-3 Controls on Cell Division • When an injury such as a cut in the skin or a break in a bone, cells alone the edges are stimulated to divide rapidly. • This action produces new cells to start the process of healing. • When the healing process is complete, the rate of cell division slows. Go to Go to Section: Section: 5 9/29/08 Uncontrolled Cell Growth Cell Cycle Regulators • The consequences of uncontrolled • Tim Hunt and Mark Kirschner cell growth in multicellular discovered that cells in mitosis organisms are very severe. contained a protein called cyclin. • Cancer is a disorder in which • If this protein is injected into a come of the body’s own cells lose non-dividing cell, it causes the the ability to control growth. formation of the spindle. • Cancer cells do not respond to the signals that regulate the growth of • It was decided that cyclins most cells. regulate the timing of the cell • They form masses called tumors cycle in eukaryotic cells. that can damage surrounding • There are internal and external tissues. regulators. Go to Go to Section: Section: Figure 10–8 Effect of Cyclins Videos Section 10-3 The sample is injected into a second cell in G2 of interphase. Click a hyperlink to choose a video. Animal Cell Mitosis A sample of Animal Cell Cytokinesis cytoplasm is removed from a cell in mitosis. As a result, the second cell enters mitosis. Go to Section: Video 1 Video 2 Animal Cell Mitosis Animal Cell Cytokinesis Click the image to play the video segment. Click the image to play the video segment. 6 9/29/08 Go Online Interest Grabber Answers 1. On a sheet of paper, make a drawing of a cell that has the following Links on cell growth dimensions: 5 cm x 5 cm x 5 cm. Your partner should draw another cell Links from the authors on stem cells about one half the size of your cell on a separate sheet of paper.
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