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Limits to Cell Size and Cell Division

This lesson explores the difficulties cells face as they increase in size, such as DNA overload and reduced efficiency in moving materials. It also explains the importance of maintaining a balanced surface area to volume ratio and the process of cell division. The lesson further compares asexual and sexual reproduction in terms of advantages and disadvantages.

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Limits to Cell Size and Cell Division

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  1. Lesson Overview 10.1 Cell Growth, Division, and Reproduction

  2. Limits to Cell Size What are some of the difficulties a cell faces as it increases in size? The larger a cell becomes, the more demands the cell places on its DNA. A larger cell is less efficient in movingmaterials.

  3. Information “Overload” Living cells store critical information in DNA. As a cell grows, more information is needed. If a cell were to grow too mcuh, an “information crisis” would occur.

  4. Information “Overload” Compare a cell to a growing town. The town library has a limited number of books. As the town grows, these limited number of books are in greater demand, which limits access. A growing cell makes greater demands on its genetic “library.” If the cell gets too big, the DNA would not be able to help the growing cell.

  5. Exchanging Materials Material move in and out based on the cell’s surface area. The rate at which materials are used up depends on the cell’s volume. The ratio of surface area to volume is key to understanding why cells must divide as they grow.

  6. Ratio of Surface Area to Volume -Imagine a cell shaped like a cube. -As the length increases, its volume increases faster than its surface area. The SA:V ratio decreases.

  7. Traffic Problems Compare to a town – As the town grows, it becomes more difficult to move information and goods. Similarly, a cell that continues to grow would experience “traffic” problems. If the cell got too large, it would be more difficult to get oxygen and nutrients in and waste out.

  8. Division of the Cell Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division. Cell division keeps a stable SA:V ratio.

  9. Cell Division and Reproduction How do asexual and sexual reproduction compare? -Asexual reproduction – Produce genetically identical offspring from a single parent

  10. -Sexual reproduction – Offspring inherit some of their genetic information from each parent.

  11. Asexual Reproduction Advantages: Quick, produces many. Disadvantages Genetically identical / no diversity

  12. Sexual Reproduction Advantages: Genetic diversity Disadvantages: Time, less produced

  13. Review • What are two reasons a large cell is problematic? • -Too much demand on DNA • -Less efficient at moving materials • What ratio decreases as a cell gets larger? • -SA:V

  14. Review • How many parents are involved in asexual reprod? • -One • How do offspring compare to the parent in A.R.? • -They are identical • How many parents are involved in sexual reprod? • -Two • 6. How do offspring compare to the parent in S.R.? • -Mix of genes

  15. Review • Fill in the information below: • -Sexual Reproduction • -Advantage: • -Genetic Diversity • -Disadvantage • -Takes time

  16. Review • 8. Fill in the information below: • -Asexual Reproduction • -Advantage: • -Quick and many produced • -Disadvantage • -No diversity

  17. Lesson Overview 10.2 The Process of Cell Division

  18. Prokaryotes Cells carry genetic information in packages of DNA called chromosomes. Most prokaryotes have only one circular stand of DNA

  19. Eukaryotes • In eukaryotes, the DNA is wound around a histone protein • Together make a nucleosome. • Chromosomes make the precise separation of DNA during cell division.

  20. DNA is condensed to form chromatin, which condense even more to form chromatids, which make up chromosomes.

  21. The Prokaryotic Cell Cycle In prokaryotes, cells go through a process of cell division known as binary fission. Binary fission = asexual reprod. = Identical offspring

  22. The Eukaryotic Cell Cycle Interphase The time betweencell divisions. Period of growth that consists of the G1, S, and G2 phases.

  23. 1. 4. 3. 2.

  24. Interphase G1 phase – cells get largerand make new materials. S (synthesis) phase – new DNA is synthesized G2 phase - preparefor cell division

  25. M Phase: Cell Division In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. Mitosis - division of nucleus. Cytokinesis – division cytoplasm.

  26. Mitosis Cytokinesis

  27. Review • How many strands of DNA do prokaryotes have? • - One • Nucleosomes are made up of what two things? • -DNA wound around a histone protein • Organize “chromatid, chromosomes, DNA, and chromatin” in order from smallest to largest. • -DNA, chromatin, chromatid, chromosome • Prokaryotes go thorugh a process of asex. reprod. called… • - Binary Fission

  28. Review • What are the four phases of the cycle cycle? • - G1, S, G2, M • G1, S, and G2 phases are all part of what? • -Interphase • What two phases make up the M Phase? • - Mitosis and Cytokinesis • What’s the difference between mitosis and cytok.? • -Mitosis – Nucleus splits • -Cytokinesis – Cytoplasm splits

  29. Important Cell Structures Involved in Mitosis • Chromatid– each strand of a duplicatedchromosome • Centromere– the area where chromatids are joined

  30. Important Cell Structures Involved in Mitosis Centrioles– organize the spindle Spindle– come from centrioles, separate the chromatids

  31. Four Steps of Mitosis: Prophase Metaphase Anaphase Telophase

  32. 1. Prophase Prophase-first phase of mitosis-chromosomes condense and becomes visible. Centrioles move to opposite sides of nucleu The nucleolus disappears and nuclear envelope breaks down.

  33. 2. Metaphase Metaphase, -second phase of mitosis-centromeres line up across the center. A spindle fiber from each pole connects to the centromere.

  34. 3. Anaphase Anaphase-third phase of mitosis-centromeres are pulled apart and each chromatid becomes a separate chromosome. The chromosomes move towards the poles.

  35. 4. Telophase Telophase,-fourth and final phase of mitosis-chromosomes unwind into chromatin. Nuclear envelope re-forms around chromosomes. Spindle breaks apart, and the nucleolus becomes visible in each daughter nucleus.

  36. Cytokinesis Not part of mitosis! Part of the M Phase Cytokinesis completes the process of cell division – it splits one cell into two.

  37. Cytokinesis – Animals vs. Plants Animals Cell membrane is drawn in until the cytoplasm is pinched into two equal parts.

  38. Cytokinesis – Animals vs. Plants Plants In plants, the cell wall prevents pinching. Instead, a cell plate forms between nuclei and becomes a cell wall.

  39. The Stages of the Cell Cycle

  40. Review • The chromatids are joined at the • -Centromere • The spindle is organized by what structures? • - Centrioles • Think of a mnemonic for the 4 stages of mitosis. • -Please Make ATake • Cytokinesis is not part of… • -Mitosis

  41. Review • Which part of mitosis do chromatids line in the middle? • -Metaphase • 6. What part does the chromosomes become visible? • -Prophase • What part does the nuclear envelope start to reform? • -Telophase • What part pulls the sister chromatid apart? • -Anaphase

  42. Lesson Overview 10.3 Regulating the Cell Cycle

  43. The Cell Cycle • Controls on cell growth and division can be turned on and off. • For example, when an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division slowswhen the healing process nears completion.

  44. The Discovery of Cyclins • Cyclins- proteins that regulate the cell cycle in eukaryotic cells. • This graph shows how cyclin levels change throughout the cell cycle in fertilized clam eggs.

  45. Regulatory Proteins • Internalregulators - respond to events insidea cell. • Allow the cell cycle to proceed only once certain processes have happened. • Externalregulators - respond to events outsidethe cell. • Direct cells to speed up or slow down the cell cycle. • Ex - Growth factors – Important during embryonic development and wound healing.

  46. Apoptosis • Apoptosis - programmed cell death. • Plays role in shapingstructure. • For example, the foot of a mouse is shaped the way it is partly because the toes undergo apoptosis during tissue development.

  47. Cancer and the Cell Cycle • Cancer - disorder in which body cells lose ability to control cell growth. • Cancer cells divide uncontrollably to form a mass of cells called a tumor.

  48. Cancer and the Cell Cycle • Benigntumor =noncancerous. • Does not spread to surrounding healthy tissue. • Malignanttumor = cancerous.It spread and destroys surrounding healthy tissue.

  49. What Causes Cancer? • Caused by defects in genesthat regulate cell growth and division. • Causes include smoking tobacco, radiation exposure, defective genes, and viral infection. • A damaged p53 gene is common in cancer cells. • Causes cells to lose the information needed to respond to growth signals.

  50. Treatments for Cancer • Some localized tumors can be removed by surgery. • Many tumors can be treated with targeted radiation. • Chemotherapyis the use of compounds that kill or slow the growth of cancer cells. • Cancer Warrior PBS

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