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Cell Biology I. Overview II. Membranes: How Matter Get in and Out of Cells

Cell Biology I. Overview II. Membranes: How Matter Get in and Out of Cells III. Cellular Respiration IV. Photosynthesis V. DNA, RNA, and Chromosome Structure VI. Protein Synthesis VII. Cellular Reproduction. VII. CELL REPRODUCTION Overview: Why Reproduce?. VII. CELL REPRODUCTION

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Cell Biology I. Overview II. Membranes: How Matter Get in and Out of Cells

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  1. Cell Biology I. Overview II. Membranes: How Matter Get in and Out of Cells III. Cellular Respiration IV. Photosynthesis V. DNA, RNA, and Chromosome Structure VI. Protein Synthesis VII. Cellular Reproduction

  2. VII. CELL REPRODUCTION Overview: Why Reproduce?

  3. VII. CELL REPRODUCTION Overview: Why Reproduce? Reproduction is selected for, by definition. X X X X

  4. - WHY?? Bigger is better…. As cells increase in size, they decrease in efficiency.

  5. - WHY?? Bigger is better…. So selection favors growth… But as cells increase in size, they decrease in efficiency.

  6. SA/V = 6 SA/V = 3 SA/V = 1.5 The “surface area to volume ratio” decreases as something increases in size….

  7. SA/V = 6 SA/V = 3 SA/V = 1.5 The “surface area to volume ratio” decreases as something increases in size…. The surface area – the membrane – limits the rate of supply of nutrients to the cell. The volume – where all the enzymes are – represents potential production and ‘demand’ for nutrients.

  8. SA/V = 6 SA/V = 3 SA/V = 1.5 So, as something gets larger, the volume increases more than the surface area… and the demand for nutrients (to meet peak productivity) grows faster than the rate at which the more slowly increasing SA can supply them. So, supply fails to meet demand, and the cell cannot meet peak productivity… it becomes less efficient.

  9. - WHY?? Bigger is better…. So selection favors growth… But as cells increase in size, they decrease in efficiency. So, to get bigger, most organisms increase cell number, not cell size….

  10. - WHY?? And with many cells, cell specialization can increase efficiency at the organismal level.

  11. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle INTERPHASE S (DNA synthesis) LE 12-5 G1 Mitosis Cytokinesis G2 MITOTIC (M) PHASE

  12. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase: a.  G1: high metabolic activity (protein synthesis) chromosomes diffuse; one DNA double helix per chromosome

  13. VIII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase: Some cell types are "stuck" in this stage when they mature... it is only "stem cells" that keep dividing.  In some tissues, all stem cells  eventually mature, so the tissue can't regenerate (neurons)

  14. LE 12-15 G0 G1 checkpoint G1 G1 If a cell does not receive a go-ahead signal at the G1 checkpoint, the cell exits the cell cycle and goes into G0, a nondividing state. If a cell receives a go-ahead signal at the G1 checkpoint, the cell continues on in the cell cycle.

  15. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase a. G1 b. S Chromosome duplication (including DNA synthesis) Centromere Sister chromatids

  16. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase a. G1 b. S c. G2

  17. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle     1.  Interphase 2. Mitosis

  18. VIII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • 1. Initiation • - Replisomes land at "origin" • - They have a variety of enzymes that work together, including: • HELICASE that unzips the double helix. • PRIMASE, an RNA POLYMERASE, that starts replication DNA POLYMERASES that make DNA.

  19. - HELICASE separates strands 5' 3' 3' 5'

  20. - HELICASE separates strands - PRIMASE lays down RNA from 5' 3' (like transcription) 3' 5' 3' 3' 5' 3'

  21. - HELICASE separates strands - PRIMASE lays down RNA from 5' 3' (like transcription) - DNA POLYMERASE - 'knocks' primase off and adds DNA bases to the free 3' OH group.... 5' 3' 3' 5'

  22. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork So, into each 'replication fork',there is "continuous synthesis" on one strand 5' "FORK" "FORK" 3' 3' 5'

  23. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork What about the other strands? 5' 3' 3' 5'

  24. VIII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork What about the other strands? PROBLEM!!! Only 5' phosphates available.....so they can't be extended 5' 5' 3' 3' 5' 5'

  25. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork The process must start again.... 5' Primase makes RNA 5' 3' 3' 3' 3' 5' Primase makes RNA 5'

  26. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork The process must start again.... DNA POLY adds DNA 5' 5' 3' 3' 5' 5' DNA POLY adds DNA

  27. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork And what happens when more DNA is opened up???? 5' 5' 3' 3' 5' 5' 5' 3'

  28. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork Continuous synthesis can continue from 3' end of DNA 5' 5' 3' 3' 5' 5' 5' 3'

  29. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork But Primase must begin the process on "lagging" strand 5' 5' 3' 3' 5' 5' 5' 5' 3'

  30. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork ...then DNA POLY can add DNA bases to "primer" 5' 5' 3' 3' 5' 5' 5' 5' 3'

  31. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork And this happens at the other fork...... DNA is opened... 3' 5' 5' 3' 5' 3' 5' 5' 5' 3'

  32. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork Continuous synthesis occurs from the free 3' end 3' 5' 5' 3' 5' 5' 5' 3' 3' 3' 5'

  33. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork Discontinuous synthesis on "lagging strand" (Primase, etc) 3' 5' 5' 5' 3' 5' 5' 5' 3' 3' 3' 5'

  34. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork So, BOTH STRAND HAVE "OKAZAKI FRAGMENTS...." 3' 5' 5' 5' 5' 3' 5' 5' 5' 3' 3' 5'

  35. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork NOW WHAT??? We have RNA in the DNA double helix 3' 5' 5' 5' 5' 3' 5' 5' 5' 3' 3' 5'

  36. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork Repair DNA Polymerases cut RNA out and add DNA to 3' 3' 5' 3' 3' 3' 3' 3' 3' 5'

  37. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork • DNA Repair Repair DNA Polymerases cut RNA out and addDNA to 3' 3' 5' 3' 3' 3' 3' 3' 3' 5'

  38. VIII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork • DNA Repair Final linkage between DNA frag's made by LIGASE 3' 5' 3' 3' 5' 3' 5' 3' 5' 3' 5' 3' H2O

  39. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork • DNA Repair Final linkage between DNA frag's made by LIGASE 3' 5' 3' 3' 5' 3' 5' 3' 5' 3' REPLICATION COMPLETE H2O

  40. VII. CELL REPRODUCTION • Overview: Why Reproduce? • A. The Cell Cycle • B. DNA Replication • Initiation • Replication at the fork • DNA Repair • Semi-conservative replication

  41. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis

  42. INTERPHASE PROPHASE PROMETAPHASE Kinetochore Centrosomes (with centriole pairs Early mitotic spindle Chromatin (duplicated) Aster Fragments of nuclear envelope Nonkinetochore microtubules Centromere LE 12-6aa Nucleus Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Nuclear envelope

  43. METAPHASE ANAPHASE TELOPHASE Nucleolus forming Metaphase plate Cleavage furrow LE 12-6ba Nuclear envelope forming Centrosome at one spindle pole Daughter chromosomes Spindle

  44. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis G2 OF INTERPHASE PROPHASE PROMETAPHASE

  45. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis LE 12-6da TELOPHASE AND CYTOKINESIS METAPHASE ANAPHASE

  46. VII. CELL REPRODUCTION Overview: Why Reproduce? A. The Cell Cycle B. DNA Replication C. Mitosis 10 µm LE 12-10 Nucleus Chromatin condensing Chromosomes Nucleolus Cell plate Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelope will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of the cell as their kinetochore micro- tubules shorten. Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is starting to form. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell.

  47. LE 12-9a 100 µm Cleavage furrow Daughter cells Contractile ring of microfilaments Cleavage of an animal cell (SEM)

  48. LE 12-9b Vesicles forming cell plate Wall of parent cell 1 µm New cell wall Cell plate Daughter cells Cell plate formation in a plant cell (TEM)

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