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The Cell Cycle

The Cell Cycle. Chapter 8. Sperm that did not make it in. 8-cell human embryo. All cells come from pre-existing cells. One characteristic that distinguishes living from non-living is the ability to reproduce Cellular reproduction allows the continuity of life, growth and repair

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The Cell Cycle

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  1. The Cell Cycle Chapter 8

  2. Sperm that did not make it in 8-cell human embryo All cells come from pre-existing cells • One characteristic that distinguishes living from non-living is the ability to reproduce • Cellular reproduction allows the continuity of life, growth and repair • Cellular reproduction can be asexual or vegetative, or sexual

  3. Asexual / Vegetative Reproduction Plant cuttings will sprout roots, as will a potato, which is a tuber – a modified, underground stem.

  4. Mold Yeast Hydra Asexual reproduction - budding Genetically identical clones

  5. All somatic cells reproduce mitotically • Somatic cells are all the cells of the body, except the gametes (egg and sperm) • Skin cells, liver cells, cells that line the G.I. tract, etc. are constantly dividing, to replace dead cells • Other cells such as neurons, adipose cells, muscle cells, etc. never or rarely divide

  6. The Cell Cycle • A typical human cell undergoes a division about every 24 hours (there are many exceptions!) • The cell cycle is basically an alternation of 2 major phases – Mitosis and Interphase • Interphase is the phase in which the cell spends 23 of the 24 hours – the cell grows, carries out its “housekeeping duties” and its specialized activities • Mitosis takes about 1 hour

  7. The Cell Cycle

  8. Phases of Interphase • G1 phase: The period prior to the synthesis of DNA. In this phase, the cell prepares for cell division - proteins are synthesized - the cell increases in mass • S phase: The period after G1, where all genetic material (DNA) is synthesized • G2 phase: The period after DNA synthesis has occurred but prior to the start of mitosis. - cell continues to increase in size - centrosome divides into 2 - In animal cells, each centrosome has 2 centrioles

  9. How DNA Packs into a Metaphase Chromosome

  10. Chromosomes A human Karyotype

  11. All somatic cells are Diploid (2n) • The cells have 2 versions of every DNA strand or chromosome • The 2 versions are called homologous chromosomes • One homologue comes from the sperm and the other from the egg • Human somatic cells have 46 chromosomes – or 23 homologous chromosome pairs

  12. DNA (chromosome) replication • The cell has to replicate (duplicate) all its DNA • The duplicated DNA is then organized into distinct bundles called chromosomes – the duplicates are connected to each other at the centromere • Each duplicated DNA strand is called a sister chromatid • Human cells still have 46 chromosomes, and 23 homologous pairs, but 92 sister chromatids

  13. (p-arm) (q-arm) DNA Replication

  14. Duplicated Chromosome

  15. The duplicated chromosome

  16. Kinetochore • It is a protein complex found in the centromere region of a chromosome • Each sister chromatid must have a kinetochore • Spindle fibers attach at the kinetochore and help pull the sister chromatids apart

  17. The mitotic spindle at Metaphase (Animal Cells only) (Animal Cells only)

  18. Centriole duplication Centrioles have microtubules arranged in 9 triplets

  19. Phases of Mitosis The cell is in Interphase (~23 hours) before it enters mitosis (1 hour). These are the phases of mitosis: • Prophase • Metaphase • Anaphase • Telophase (followed immediately by cytokinesis)

  20. Phases of Mitosis G2 of Interphase Metaphase Prometaphase Prophase Anaphase Telophase & beginning of cytokinesis Completion of cytokinesis

  21. Prophase • Chromatin condenses into chromosomes • Nucleolus begins to disappear • Centrioles duplicate and start to move apart • Centrioles start making spindle fibers

  22. Prophase, continued • Nuclear membrane begins to disappear • This allows spindle fibers to attach the chromosomes • Centrioles are at opposite poles of the cell

  23. Metaphase • The chromosomes are aligned at the equator of the cell – called the metaphase plate

  24. Anaphase • Sister chromatids pull apart and are now considered daughter chromosomes • At the end of anaphase, each group of chromosomes is clustered at opposite poles.

  25. Telophase • In animal cells, the cleavage furrow begins to form • Nuclear membrane begins to re-form • The spindle fibers begin to disassemble • Chromosomes begin to return to chromatin state • Nucleolus begins to reappear • Cytokinesis takes place

  26. Centrioles will replicate once the cell is ready to divide again Interphase • Nucleus contains chromatin • Only one set of centrioles (one centrosome) • Fully formed nuclear membrane • Fully formed nucleolus

  27. PROPHASE

  28. PROMETAPHASE

  29. METAPHASE

  30. ANAPHASE

  31. TELOPHASE

  32. Cytokinesis in Animal Cells Cleavage Furrow Contractile ring made of actin microfilaments, “pinches” the cell into two.

  33. Cytokinesis in Plant Cells Plant cells cannot be “pinched” into two new daughter cells, because of the cell wall. The Golgi body secretes cell wall material packaged in transport vesicles that line up on the equator. These vesicles fuse to create a cell plate. The cell plate divides the cell in two. The cell plate becomes the cell wall.

  34. Gametes Eggs and sperm are called gametes All other cells of the body are called somatic cells Eggs develop in the ovaries and sperm develop in the testes. All eggs and sperm develop from cells called PGCs or Primordial germ cells PGCs are diploid – 46 chromosomes

  35. Diploid vs. Haploid A cell that has both members of a homologous pair of chromosomes in the nucleus, is considered to be Diploid (2n) A cell that has only one homologue of a chromosome pair (so either the maternal or paternal homologue is missing) is considered Haploid (n)

  36. Importance of Meiosis Reduces the number of chromosomes by half – the cell goes from diploid (2n) to haploid (n) – humans go from 23 pairs to 23 single chromosomes Prevents polyploidy (multiple chromosomes) – and maintains the chromosome number of each species Produces genetic variation and contributes to evolution

  37. Primordial Germ Cell (PGC) Found in ovaries and testes These cells are diploid (2n) so they have 23 pairs of chromosomes or 46 total.

  38. The Human Life Cycle

  39. Prophase I of Meiosis Homologous chromosomes pair up with each other The sister chromatids of each pair CROSSOVER with each other and swap pieces of DNA This creates variation in the chromosomes of the gametes that will form

  40. THE END

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