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Cellular reproduction

……………………………………………. Cellular reproduction. Reproduction is a characteristic of life. Reproduction of individuals depends on the reproduction at the cellular layer. review. From the cell theory, all cells arose from pre existing cells Nucleus- control center of the cell

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Cellular reproduction

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  1. ……………………………………………... Cellular reproduction

  2. Reproduction is a characteristic of life. • Reproduction of individuals depends on the reproduction at the cellular layer Carina Perete DVM

  3. review • From the cell theory, all cells arose from pre existing cells • Nucleus- control center of the cell • Nucleus contains chromosomes which bear the genes • Nucleus carries “blueprint” Carina Perete DVM

  4. Genes- unit of information passed from generation to generation -determine the characteristics of each new organism and directs its many activities • when the cell divides, the nuclear information must be transmitted in orderly fashion to the new cells Carina Perete DVM

  5. Asexual Reproduction in Bacteria • Bacteria reproduce asexually by binary fission. • A bacterium possesses a single, circular chromosome which is replicated; and then the replicates (chromosomes) are distributed to two new cells formed by division of the original cell. Carina Perete DVM

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  8. The eukaryotic cell cycle The eukaryotic cell cycle has 5 main phases: 1. G1 (gap phase 1) 2. S (synthesis) 3. G2 (gap phase 2) 4. M (mitosis) 5. C (cytokinesis) The length of a complete cell cycle varies greatly among cell types. Carina Perete DVM

  9. The Eukaryotic Cell Cycle • Interphase • G1 growth phase; synthesis of organelles • S synthesis of DNA (replication) • G2 growth; synthesis of proteins essential to cell division • -each chromosome in the cell consists of two identical sister chromatids • Cell is preparing to divide Carina Perete DVM

  10. Mitosis • prophase • metaphase • anaphase • telophase Carina Perete DVM

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  12. Types of Cell Division • Mitosis • provides cells for growth, cell replacement, and asexual reproduction • maintains chromosome number • Meiosis • produces cells for sexual reproduction • reduces chromosome number by half Carina Perete DVM

  13. Important Terms • chromatin - the form taken by chromosomes when a eukaryotic cell is not dividing • monad chromosome - unreplicated chromosome (single chromosome) • dyad chromosome - replicated chromosome (double chromosome) • chromatid - half of a dyad chromosome • centromere - structure by which chromatids of a dyad chromosome are held together Carina Perete DVM

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  16. Mitosis* • Part of the cell cycle where the cell is actually dividing • Nucleus and its contents divide and are evenly distributed forming 2 daughter nuclei Carina Perete DVM

  17. Prophase: dyad (replicated) chromosomes resemble long threads (chromatin) • replicated centrioles move apart toward opposite poles; (animal cell) • nucleolus disappears; dyad chromosomes condense (coil tightly); Carina Perete DVM

  18. nuclear membrane disintegrates • spindle fibers appear between centrioles; dyad chromosomes migrate toward the equator of the cell Carina Perete DVM

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  20. Promethaphase Prometaphase: -chromosomes become attached to the spindle apparatus by their kinetochores -a second set of microtubules is formed from the poles to each kinetochore -microtubules begin to pull each chromosome toward the center of the cell Carina Perete DVM

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  23. Mitosis* • 2. Metaphase: dyad chromosomes line up along the equator of the cell Carina Perete DVM

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  25. Mitosis* • 3. Anaphase: dyad chromosomes separate forming monad chromosomes; monad chromosomes move toward opposite poles Carina Perete DVM

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  27. Mitosis* • 4. Telophase: monad chromosomes cluster at poles; cytokinesis occurs gradually; nuclear membrane forms; nucleolus reappears; chromosomes uncoil; cytokinesis is completed; two daughters cells are formed Carina Perete DVM

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  30. cytokinesis Cytokinesis – cleavage of the cell into equal halves -in animal cells – constriction of actin filaments produces a cleavage furrow -in plant cells – plasma membrane forms a cell plate between the nuclei -in fungi and some protists – mitosis occurs within the nucleus; division of the nucleus occurs with cytokinesis Carina Perete DVM

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  32. Daughter Cells of Mitosis • have the same number of chromosomes as each other and as the original cell from which they were formed • e.g. Mitosis in a cell which possesses 4 chromosomes will result in the formation of two daughter cells each having 4 chromosomes. Carina Perete DVM

  33. Types of Cell Division • Mitosis • provides cells for growth, cell replacement, and asexual reproduction • maintains chromosome number • Meiosis • produces cells for sexual reproduction • reduces chromosome number by half Carina Perete DVM

  34. Meiosis • preceded by interphase which includes chromosome replication • two meiotic divisions • four daughter cells produced • daughter cells contain half the number of chromosomes as the original cell Carina Perete DVM

  35. Important terms in the study of meiosis • monad chromosome - unreplicated chromosome • dyad chromosome - chromosome composed of two chromatids (replicates) • homologous - similar in size and shape • synapsis - pairing of homologous chromosomes • crossover - exchange of segments between chromatids of homologous chromosomes Carina Perete DVM

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  37. Chromosomes are replicated during S-phase of interphase. As a result, monad chromosomes become dyad chromosomes. Carina Perete DVM

  38. Meiosis I • Prophase I: homologous chromosomes of diploid cell synapse; homologous pairs migrate toward equator of cell; crossover may occur during synapsis • Metaphase I: dyad pairs of homologous chromosomes align at the equator of the cell Carina Perete DVM

  39. Anaphase I: homologous chromosomes move apart toward opposite poles • Telophase 1: chromosomes cluster at poles of cell; cytokinesis occurs forming two haploid daughter cells each containing one member of each homologous pair thus reducing chromosome by half Carina Perete DVM

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  41. Meiosis II (resembles mitosis) • Prophase II: dyad chromosomes move toward the equator of each cell (2) • Metaphase II: dyad chromosomes align at equator of cell • Anaphase II: dyad chromosomes separate forming monad chromosomes (chromatids separate); monads migrate toward opposite poles of each cell Carina Perete DVM

  42. Telophase II: cytokinesis occurs at right angles to the first plane of division in each cell (2); four daughter cells are formed each having half the number of chromosomes as the original cell Carina Perete DVM

  43. Gamete formation - meiosis • meiosis in males – spermatogenesis • meiosis in females - oogenesis Carina Perete DVM

  44. Spermatogenesis • 4 mature sperm cells produced from meiosis in a single spermatocyte Carina Perete DVM

  45. Oogenesis • one mature ovum (egg cell) and 3 polar bodies formed from meiosis in a single oocyte • human female embryo - oocytes formed by mitosis and then complete prophase I of meiosis by time of birth • puberty - one oocyte in alternating ovaries resumes meiosis under the influence of hormones; at ovulation the oocyte is at metaphase II • oogenesis will be completed in the event of fertilization Carina Perete DVM

  46. Comparison of Mitosis and Meiosis • Mitosis • synapsis does not occur • one division occurs • two daughter cells are formed • chromosome number is maintained • Meiosis • synapsis occurs during Prophase I • two divisions occur • four daughter cells are formed • chromosome number is reduced by half Carina Perete DVM

  47. Apoptosis • Apoptosis is programmed cell death and involves a sequence of cellular events involving: • fragmenting of the nucleus, • blistering of the plasma membrane, and • engulfing of cell fragments by macrophages and/or neighboring cells. • Apoptosis and cell division are balancing processes that maintain the normal level of somatic (body) cells. Carina Perete DVM

  48. Cells normally hold caspases in check with inhibitors. • Caspases are released by internal or external signals. Carina Perete DVM

  49. Cell death is a normal and necessary part of development: frogs, for example, must destroy tail tissue they used as tadpoles, and the human embryo must eliminate webbing found between fingers and toes. • Death by apoptosis prevents a tumor from developing. Carina Perete DVM

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