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Cell Reproduction

Cell Reproduction. 8.1 – Chromosomes 8.2 – Cell Division 8.3 - Meiosis. What factors limit cell size?. Diffusion DNA Content Surface area-to-volume ratio. DIFFUSION. Certain materials needed for the survival of the cell can only enter through diffusion.

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Cell Reproduction

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  1. Cell Reproduction 8.1 – Chromosomes 8.2 – Cell Division 8.3 - Meiosis

  2. What factors limit cell size? • Diffusion • DNA Content • Surface area-to-volume ratio

  3. DIFFUSION • Certain materials needed for the survival of the cell can only enter through diffusion. Ex. waste, carbon dioxide, oxygen • Diffusion is only efficient over a short distance. • A 20 cm cell would have to wait several months to receive the above listed molecules

  4. DNA CONTENT • Most cells have only 1 nucleus • The DNA in the nucleus makes RNA and releases it to the cytoplasm where it directs the production of enzymes • Lack of enzymes = Lack of cellular metabolism • Some large cells have compensated by having multiple nuclei.

  5. Surface area-to-volume ratio • If you double the size of a cell… -It has 8x as much volume -Gives rise to 8x as much waste and need for nutrients -It becomes impossible for diffusion to keep up with the cellular demands

  6. Chromosomes • Rod-shaped structures made of DNA and protein • Coiled chromatin =chromosomes • Histones = proteins that help maintain the shape of the chromosome

  7. Types of Chromosomes • Sex Chromosomes • X or Y chromosomes • Determine sex of individual • Autosomes • Non-sex chromosomes • Determine all other characteristics or traits • Ex. Hair color, eye color, hemophilia

  8. Chromosome Number • Diploid • Having 2 sets of chromosomes (2n) • Creates genetic diversity • Hapliod • Contain one set of chromosomes (n) • Sex cells

  9. Two major stages of the cell cycle • Interphase – the growth period of time where cell activities are carried out -most of the cells life • Mitosis – process of nuclear division, followed by the division of the cytoplasm

  10. INTERPHASE • What is going on during this time? • G1 Phase • Metabolism – making ATP • Cell growth, maintenance, repair • S Phase • Chromosomes are replicated (ready for mitosis) • Make new proteins • Synthesizing new organelles • Conducting photosynthesis (autotrophs) • Storing excess glucose (starch, glycogen) • G2 Phase • Final preparation before cell division (mitosis)

  11. Stages of Mitosis • Prophase • Metaphase • Anaphase • Telophase

  12. PROPHASE • First stage of mitosis • Longest phase of mitosis • Chromatin the nucleus becomes visible chromosomes • Nucleus disappears • The chromatin, which was copied during interphase forms 2 complete sets of chromosomes called sister chromatids • Spindle fibers form between pairs of centrioles

  13. METAPHASE • Second stage of mitosis • Chromosomes move to the equator of the cell • Spindle fibers attach to each chromatid by its centromere

  14. ANAPHASE • Third stage of mitosis • Chromosomes separate at the centromere • Each sister chromatid begins to move to opposite ends of the cell

  15. TELOPHASE • Fourth stage of mitosis • Two daughter cells are formed • Each new cell has a complete set of chromosomes • The cytoplasm then divides (cytokinesis) • Nucleus reappears • Chromosomes uncoil to form chromatin • Interphase begins

  16. Control of the Cell Cycle • Cellular enzymes and genes play a key role in checking and balancing cell division • Tells cells when to divide/stop • Proto-oncogene – regulates cell growth, division and the ability for cells to adhere to one another • Mutation of the proto-oncogene causes an oncogene • ONCOGENE = UNCONTROLLED CELL DIVISION

  17. Control of the Cell Cycle (2) • Contact inhibition – cell to cell communication between neighboring cells…stops the cellular division • Eliminates an over-production of certain types of cells within the body.

  18. CANCER – a loss of control • Cancer – an uncontrolled dividing of cells • Caused by a change in one or more of the genes synthesizing enzymes to control the cell cycle (genetic factor) • The cancer genes are often expressed when environmental conditions change (environmental factor)

  19. How can cells regain control • Some genes act as brakes to suppress cancer expression • Tumor-suppressor genes – code for proteins that prevent cell division from occurring too often • To get cancer, these tumor suppressor genes (all 3 of them) must be damaged

  20. Carcinogen • Any substance that can induce or promote cancer • Most carcinogens are mutagens • Cause mutation within the cell • Known carcinogens include: • Chemicals in tobacco smoke • Radiation • UV light • Certain viruses

  21. MEIOSIS

  22. INTERPHASE

  23. INTERPHASE MAIN EVENTS • Chromatin replicates • Just like in mitosis • Forms 2 identical chromatids • Centriole pairs replicate (animal cells only)

  24. PROPHASE I

  25. PROPHASE I MAIN EVENTS • Chromatin condenses into chromosomes • Tetrad forms by synapsis • Crossing over occurs between homologous chromosomes • Centriole pairs move apart • Nuclear envelope and nucleoli disappear

  26. METAPHASE I

  27. METAPHASE I MAIN EVENTS • Tetrads align along the metaphase plate • Centromeres of homologous chromosomes point toward opposite poles • Attach to spindle fibers

  28. ANAPHASE I

  29. ANAPHASE I MAIN EVENTS • Homologous chromosomes separate • Sister chromatids move as a unit • remain attached at the centromere

  30. TELOPHASE I AND CYTOKINESIS

  31. TELOPHASE I MAIN EVENTS • Chromosomes reach poles • Still as sister chromatids • Cytokinesis occurs simultaneously • Interkinesis • No DNA replication before meiosis II

  32. MEIOSIS II MAIN EVENTS • Very similar to mitosis • PII – spindles form • MII – chromosomes align • AII – centromeres split • TII – nuclei reform • Cytokinesis – 4 haploid cells

  33. PROPHASE II

  34. METAPHASE II

  35. ANAPHASE II

  36. TELOPHASE II AND CYTOKINESIS

  37. KEY DIFFERENCES BETWEEN MEIOSIS AND MITOSIS… • Meiosis is reduction division • 2n to n • Meiosis creates genetic variation • Meiosis is 2 successive nuclear divisions • Meiosis I separates pairs of chromosomes; centromeres do not divide

  38. GAMETE PRODUCTION THROUGH MIEOSIS • Spermatogenesis • Creates 4 sperm cells • Oogenesis • Creates 1 ootid (egg cell) • 3 polar bodies (nonfunctional)

  39. ASEXUAL REPRODUCTION • Production of offspring from one parent without the union of gametes • Occurs only by mitosis

  40. SEXUAL REPRODUCTION • Production of offspring through meiosis and the union of gametes • Offspring genetically different due to genetic recombination • Parts of chromatids can be exchanged (crossing over) • Homologous pairs separate

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