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Cell Growth and Division: Limits and Chromosome Characteristics

This chapter explores the limits to cell growth, including the problems it causes and the importance of surface area to volume ratio. It also examines the process of cell division and the characteristics of chromosomes.

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Cell Growth and Division: Limits and Chromosome Characteristics

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  1. Chapter 8 Cell Growth and Division

  2. Limits to Cell Growth  What problems does growth cause for cells?  The larger a cell becomes, the more demands a cell places on its DNA and the harder it is for the cell to move enough nutrients and wastes across the cell membrane.  Think of a library. If the amount of books doesn’t change and the town continues to grow, will the library be able to meet the needs of the community?

  3. Limits to Cell Growth  The rate at which food, oxygen, water, and wastes are moved in and out of the cell is dependent on the surface area of the cell.  The rate at which food, oxygen, and water are used and waste is produced depends on the cell’s volume.

  4. Limits to Cell Growth  Ratio of Surface Area to Volume - As the length of a cell increases, its volume increases faster than the surface area. - The decrease in the cell’s ratio of surface area to volume makes it more difficult for the cell to move needed materials in and waste products out quickly enough for the cell to survive.

  5. Limits to Cell Growth

  6. Division of the Cell  Before it becomes too large, a growing cell divides forming two “daughter” cells.  The process by which a cell divides into two new daughter cells is called cell division.

  7. 8–1 Review  As a cell increases in size, which of the following increases most rapidly? • surface area • volume

  8. 8–1 Review  If an imaginary cube-shaped cell has a length of 6 cm, its ratio of surface area to volume is • 1 : 1. • 6 : 1. • 36 : 1. • 1 : 6.

  9. 8–1 Review  The process by which a cell divides into two new daughter cells is called • cell growth. • cell division. • DNA replication. • cell multiplication.

  10. 8–1 Review  When one cell divides in two, what happens to the surface area to volume ratios in the new cells? • There is no change in the amount of material exchanged. • Each new cell can exchange more material than the original cell. • Each new cell can exchange less material than the original cell. • The two new cells cannot be compared to the original cell.

  11. 8–1 Review  When a growing cell undergoes cell division, each new cell gets • half the DNA from the original cell. • twice as much DNA as the original cell. • a random sample of the DNA in the original cell. • a full copy of all the DNA in the original cell.

  12. Chromosomes  Eukaryotic cells: during cell division, DNA is coiled tightly into compact structures called chromosomes. - Rod-shaped structures made of DNA and protein.

  13. Chromosomes (cont’d)  Between cell divisions, DNA is not so tightly coiled into chromosomes and is called chromatin.

  14. Chromosomes (cont’d)  Each chromosome consists of two identical “sister” chromatids. Sister chromatids  Each pair of chromatids is attached at an area called the centromere.  When the cell divides, the chromatids separate. Centromere  Each new cell gets one chromatid.

  15. Chromosome Number  Each species has a characteristic chromosome number  Human beings have 46 chromosomes.  Dogs have 78 chromosomes.  The number of chromosomes does NOT determine the complexity of the organism.

  16. Human Karyotype

  17. Chromosome Number (cont’d)  Chromosomes are characterized as 2 types: - Sex chromosomes – determines the sex of an organism; may carry genes for other characteristics. - Autosomes – represent all of the other chromosomes.

  18. Sex Chromosomes  Humans have 2 sex chromosomes: X or Y.  Normal females have XX and males have XY. 19

  19. Autosomes • All other chromosomes • Humans have 2 sex chromosomes and 44 autosomes. 20

  20. Homologous Chromosomes • Every cell produced by sexual reproduction has 2 copies of each autosome. - One from each parent. • The 2 copies are homologous chromosomes or homologues. 21

  21. Homologous Chromosomes (cont’d) • Same size and shape and carry genes for the same traits. • Humans have 22 homologous pairs and 2 sex chromosomes. 22

  22. Diploid • Represented by 2n. • Cells with 2 sets of chromosomes, with both chromosomes for each homologous pair. 23

  23. Diploid (cont’d) • Cells also have 2 sex chromosomes. • All normal human cells, except reproductive cells (sperm cells and egg cells), are diploid. • Humans have a diploid number of 46. 24

  24. Haploid • Represented by 1n or n. • Human sperm and egg cells have only one set of chromosomes, which is half the number in a diploid. 25

  25. Haploid (cont’d) • Haploid cells contain only one chromosome of each homologous pair and only one sex chromosome. • When a sperm (1n) and an egg (1n) combine, they form a cell which is diploid (2n). 26

  26. Cell Division: Prokaryotes Divide by binary fission division into 2 offspring. 27

  27. Cell Division: Prokaryotes • 3 stages: Chromosome copies itself. Cell grows to twice the original size. Cell wall forms between the 2 chromosomes and cell splits into 2 new cells, identical to the original. 1. 2. 3. 28

  28. Cell Division  In eukaryotes, cell division occurs in two major stages.  The first stage, division of the cell nucleus, is called mitosis.  The second stage, division of the cell cytoplasm, is called cytokinesis.  Reproduction by mitosis is considered asexual, since the cells produced by mitosis are genetically identical to the parent cell.

  29. The Cell Cycle  The cell cycle is the series of events that cells go through as they grow and divide.  During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins to cycle again.  Interphase is the period of growth that occurs between cell divisions.

  30. The Cell Cycle  The cell cycle consists of four phases: • G1(First Gap Phase) • S Phase • G2(Second Gap Phase) • M Phase

  31. Events of the Cell Cycle  Events of the Cell Cycle • During the normal cell cycle, interphase can be quite long, but the process of cell division takes place quickly. • Interphase is divided into three phases: G1, S, and G2. • During G1, the cell,  increases in size (this is where cells do most of their growing)  synthesizes new proteins and organelles

  32. Events of the Cell Cycle  During the S phase, • chromosomes are replicated • DNA synthesis takes place  Once a cell enters the S phase, it usually completes the rest of the cell cycle.

  33. Events of the Cell Cycle  The G2Phase (Second Gap Phase) • When the DNA replication is completed, the cell enters the G2 phase – the shortest of the three phases of interphase! • Organelles and molecules required for cell division are produced during this phase. • Once G2is complete, the cell is ready to start the M phase—Mitosis.

  34. Events of the Cell Cycle Cell Cycle

  35. Mitosis  Biologists divide the events of mitosis into four phases: • Prophase • Metaphase • Anaphase • Telophase

  36. Mitosis Section 10-2 Prophase  Prophase Spindle forming Chromosomes (paired chromatids) Centromere

  37. Mitosis Centriole  Prophase • Prophase is the first and longest phase of mitosis. • The centrioles separate and take up positions on opposite sides of the nucleus. Spindle forming Centromere Chromosomes (paired chromatids)

  38. Mitosis Centriole • The centrioles lie in a region called the centrosome. • The centrosome helps to organize the spindle, a fanlike microtubule structure that helps separate the chromosomes. Spindle forming Centromere Chromosomes (paired chromatids)

  39. Mitosis Centriole Spindle forming • Chromatin condenses into chromosomes. • The centrioles separate and a spindle begins to form. • The nuclear envelope breaks down. Centromere Chromosomes (paired chromatids)

  40. Mitosis  Metaphase Centriole Spindle Centriole Metaphase

  41. Mitosis Centriole  Metaphase • The second phase of mitosis is metaphase. • The chromosomes line up across the center of the cell. • Microtubules connect the centromere of each chromosome to the poles of the spindle. Spindle

  42. Mitosis  Anaphase Individual chromosomes Anaphase

  43. Mitosis Individual chromosomes  Anaphase • Anaphase is the third phase of mitosis. • The sister chromatids separate into individual chromosomes. • The chromosomes continue to move until they have separated into two groups.

  44. Mitosis  Telophase Nuclear envelope reforming Telophase

  45. Mitosis  Telophase • Telophase is the fourth and final phase of mitosis. • Chromosomes gather at opposite ends of the cell and lose their distinct shape. • A new nuclear envelope forms around each cluster of chromosomes.

  46. Cytokinesis Cytokinesis Cytokinesis

  47. Cytokinesis  During cytokinesis, the cytoplasm pinches in half.  The area of the cell membrane that pinches in half is the cleavage furrow.  Each daughter cell has an identical set of duplicate chromosomes.

  48. Cytokinesis: Animals

  49. Cytokinesis  In plants, a structure known as the cell plate forms midway between the divided nuclei. Cell plate Cell wall

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