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Mitosis, Meiosis, and the Prokaryotes

Mitosis, Meiosis, and the Prokaryotes. Eukaryotic cells Mitosis copies DNA and divides a nucleus, producing two identical nuclei Meiosis nuclear division that produces haploid gametes for sexual reproduction. Comparison of Cell Division Mechanisms. Key Points About Chromosome Structure.

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Mitosis, Meiosis, and the Prokaryotes

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  1. Mitosis, Meiosis, and the Prokaryotes • Eukaryotic cells • Mitosis copies DNA and divides a nucleus, producing two identical nuclei • Meiosisnuclear division that produces haploid gametes for sexual reproduction

  2. Comparison of Cell Division Mechanisms

  3. Key Points About Chromosome Structure • Humans have 23 (or is it 46?) chromosomes that differ in length and shape • Each consists of one double strand of DNA • After duplication, each consists of two double strands (sister chromatids) that remain attached to each other at a centromere

  4. A Chromosome and Sister Chromatids

  5. B When a chromosome is at its most condensed, the DNA is packed into tightly coiled coils. centromere multiple levels of coiling of DNA and proteins C When the coiled coils unwind, a molecule of chromosomal DNA and its associated proteins are organized as a cylindrical fiber. A Duplicated human chromosome in its most condensed form. If this chromosome were actually the size shown in the micrograph, its two DNA strands would stretch out about 800 meters (0.5 miles). fiber D A loosened fiber shows a “beads-on-a-string” organization. The “string” is the DNA molecule; each “bead” is one nucleosome. beads on a string DNA double helix core of histones E A nucleosome consists of part of a DNA molecule looped twice around a core of histone proteins. nucleosome Stepped Art Fig. 9-3 (b-e), p. 143

  6. G1 S Interval of cell growth before DNA replication (chromosomes unduplicated) Interval of cell growth when the DNA is replicated (all chromosomes duplicated) G2 Interval after DNA replication; the cell prepares to divide cytoplasmic division; each descendant cell enters interphase Telophase G2 Anaphase Metaphase Prophase Interphase ends for parent cell Stepped Art Fig. 9-4, p. 144

  7. Interphase • Interphasecell increases in size and duplicates its DNA • G1: growth and activity • S: DNA replication (synthesis) • G2: cell prepares for division

  8. Mitosis and the Chromosome Number • Mitosis produce 2 diploid nuclei with same number and kind of chromosomes as parent • Human somatic cells have 46 chromosomes paired in 23 sets (diploid number) • Pairs have same shape and information about same traits (except sex chromosomes XY)

  9. Bipolar Spindle Separates Sister Chromatids

  10. Mitosis Maintains Chromosome Number Karyotype

  11. A Closer Look at Mitosis • ** DO NOT WRITE DOWN & MEMORIZE EACH STEP! • When a nucleus divides each new nucleus has same chromosome number as parent cell • Four main stages of mitosis: prophase, metaphase, anaphase, and telophase

  12. Fig. 9-6 (2), p. 147

  13. A Early Prophase Mitosis begins. In the nucleus, the chromatin begins to appear grainy as it organizes and condenses. The centrosome is duplicated. Fig. 9-6 (2a), p. 147

  14. B Prophase The chromosomes become visible as discrete structures as they condense further. Microtubules assemble and move one of the two centrosomes to the opposite side of the nucleus, and the nuclear envelope breaks up. Fig. 9-6 (2b), p. 147

  15. C Transition to Metaphase The nuclear envelope is gone, and the chromosomes are at their most condensed. Microtubules of the bipolar spindle assemble and attach sister chromatids to opposite spindle poles. Fig. 9-6 (2c), p. 147

  16. D Metaphase All of the chromosomes are aligned midway between the spindle poles. Microtubules attach each chromatid to one of the spindle poles, and its sister to the opposite pole. Fig. 9-6 (2d), p. 147

  17. E Anaphase Motor proteins moving along spindle microtubules drag the chromatids toward the spindle poles, and the sister chromatids separate. Each sister chromatid is now a separate chromosome. Fig. 9-6 (2e), p. 147

  18. F Telophase The chromosomes reach the spindle poles and decondense. A nuclear envelope begins to form around each cluster; new plasma membrane may assemble between them. Mitosis is over. Fig. 9-6 (2f), p. 147

  19. 9.4 Cytoplasmic Division Mechanisms • Cytokinesis • The process of cytoplasmic division

  20. Fig. 9-7a, p. 148

  21. 1 Mitosis is completed, and the bipolar spindle is starting to disassemble. Fig. 9-7a (1), p. 148

  22. Fig. 9-7a (2), p. 148

  23. Fig. 9-7a (3), p. 148

  24. 3 This contractile ring pulls the cell surface inward as it continues to contract. Fig. 9-7a (3), p. 148

  25. Fig. 9-7a (4), p. 148

  26. 4 The contractile ring contracts until the cytoplasm is partitioned and the cell pinches in two. Fig. 9-7a (4), p. 148

  27. The Importance of Timing and Completion of Cell Cycle Events

  28. When Control is Lost • Sometimes, controls over cell division are lost • Cancer may be the outcome

  29. Cell Cycle Controls • Checkpoints in cell cycle allow problems to be corrected before cycle advances • Proteins produced by checkpoint genes interact to advance, delay, or stop the cell cycle • Kinases can activate other molecules to stop the cell cycle or cause cells to die • Growth factors can activate kinases to start mitosis

  30. Checkpoint Failure and Tumors • When all checkpoint mechanisms fail, a cell loses control over its cell cycle and may form a tumor (abnormal mass) in surrounding tissue • Usually one or more checkpoint gene products are missing in tumor cells • Tumor suppressor gene products inhibit mitosis • Protooncogene products stimulate mitosis

  31. Neoplasms • Neoplasms • Abnormal masses of cells that lack control over how they grow and divide • Benign neoplasms (such as ordinary skin moles) stay in one place and are not cancerous • Malignant neoplasms are cancerous

  32. Characteristics of Cancer Cells • Cancers (malignant neoplasms) • Cells grow and divide abnormally; capillary blood supply to the cells may increase abnormally • Cells may have altered plasma membrane and cytoplasm; metabolism may shift toward fermentation • Cells have altered recognition proteins and weakened adhesion; may break away and invade distant tissues (metastasis)

  33. benign tumor malignant tumor A Cancer cells break away from their home tissue. B The metastasizing cells become attached to the wall of a blood vessel or lymph vessel. They release digestive enzymes onto it. Then they cross the wall at the resulting breach. C Cancer cells creep or tumble along inside blood vessels, then leave the bloodstream the same way they got in. They start new tumors in new tissues. Fig. 9-11, p. 151

  34. Skin Cancers

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