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THE CELL CYCLE

THE CELL CYCLE. Campbell and Reece Chapter 12. Functions of Cell Division. Reproduction Growth & Development Tissue Renewal. The Cell Cycle. life of a cell from time it is 1 st formed to time it divides into 2 daughter cells in the process it passes along identical genetic material.

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THE CELL CYCLE

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  1. THE CELL CYCLE Campbell and Reece Chapter 12

  2. Functions of Cell Division • Reproduction • Growth & Development • Tissue Renewal

  3. The Cell Cycle • life of a cell from time it is 1st formed to time it divides into 2 daughter cells • in the process it passes along identical genetic material

  4. Genome • cells genetic information (DNA) • 2 m DNA in typical eukaryotic cell • for cell to divide all the DNA must be replicated then separate so each daughter cell has complete genome

  5. Chromosomes • eukaryotic structure • 1 long DNA molecule associated w/proteins = chromatin • each has several 100 to thousands of genes • associated proteins maintains structure of chromosome & help control activity of genes

  6. Cells • somatic cells: all body cells except gametes • gametes: reproductive cells, sperm & egg

  7. Parts of a Chromosome

  8. Duplicated Chromosomes

  9. Duplicated Chromosome

  10. Cell Cycle • 2 main parts: • Interphase • G1 • S • G2 • M-Phase • Mitosis • Cytokinesis

  11. A Closer Look @ Mitotic Spindle • begins to form in cytoplasm during prophase • made up of microtubules (made of protein tubulin) + associated proteins • material for assemblage of microtubules comes from disassembly of other microtubules in cell

  12. The Mitotic Spindle in Animal Cells • assembly of microtubules begins @ centrosome • pair of centrioles @ center of centrosome • not essential, spindle forms if destroyed

  13. The Mitotic Spindle in Animal Cells • single centrosome duplicates during interphase • 2 centrosome separate & move apart during prophase  @ opposite poles by prometaphase

  14. Parts of Mitotic Spindle • Centrosomes • Spindle microtubules • Asters

  15. Kinetochore • protein structure attached to centromere that links each sister chromatid to mitotic spindle

  16. Kinetochore • chromosomes 2 kinetochores face in opposite directions • spindles that attach to kinetochore in prometaphase called kinetochore microtubules • #s attached vary by species

  17. Mitotic Spindle • when 1 of chromosome’s kinetochore is “captured” by microtubules the chromosome begins to move toward the pole from which those microtubules extend • “tug-of-war” between 2 sides until @ metaphase all duplicated chromosomes on plane midway between the spindle’s 2 poles

  18. Metaphase Plate • imaginary cell structure • midway between 2 poles of spindle • nonkinetochore microtubules elongate & interact with other like kinetochores from opposite pole

  19. INTERPHASE • ~90% of cell cycle • 3 parts

  20. G1 of INTERPHASE • cell growth: • size increases • organelles made

  21. S PHASE of INTERPHASE • chromosomes duplicated • each chromosome made up of sister chromatids with same genetic information

  22. G2 of INTERPHASE • nuclear envelope intact • 1 or more nucleoli • centrosomes duplicate • 2 centrioles in each • duplicated chromosomes not yet condensed

  23. G2 of INTERPHASE

  24. PROPHASE • chromatin condenses into chromosomes becoming visible • nucleoli disappear • mitotic spindle begins to form • centrosomes move away from each other (propelled partly by lengthening microtubules between them)

  25. PROPHASE

  26. PROMETAPHASE • nuclear envelope fragments • microtubules from each centrosome now invade nuclear space • more condensation of chromatin  chromosomes • kinetochore on each sister chromatid • kinetochore microtubules begin to attach • nonkinetochore microtubules begin to interact

  27. PROMETAPHASE

  28. METAPHASE • centrosomes @ opposite poles • chromosomes @ metaphase plate • kinetochores of sister chromatids attached to microtubules from opposite poles

  29. METAPHASE

  30. ANAPHASE • shortest stage of mitosis • begins when cohesin proteins are cleaved allowing sister chromatids to separate (each chromatid now a chromosome) • each daughter chromosome moves toward opposite poles as its kinetochore microtubule shortens • Cell elongates as nonkinetochore microtubules lengthen • @ end of anaphase each pole of cell has complete set of chromosomes

  31. ANAPHASE

  32. TELOPHASE • 2 daughter nuclei form • nuclear envelopes form from fragments of parent cell’s nuclear envelope • nucleoli reappear • chromosomes become less condensed • remaining spindle microtubules depolymerize • Mitosis (nuclear division) is complete!

  33. TELOPHASE

  34. CYTOKINESIS • division of cytoplasm • usually begins in telophase • animal cells: cleavage furrow • plant cells: cell plate • ends with 2 daughter cells genetically identical to parent cell

  35. CYTOKINESIS

  36. Cytokinesis Animal Cells • occurs by process known as cleavage • on cytoplasmic side ring of actin microfilaments w/myosin molecules causes ring to contract (like pulling a drawstring • cleavage furrow deepens until cell is pinched in 2 • during telophase, vesicles (containing cell wall materials) from Golgi move along microtubules to center of cell • contents of vesicles forms cell plate Plant Cells

  37. Binary Fission • asexual reproduction in prokaryotic cells • single loop of DNA & associated proteins carries most of genes • No mitosis in prokaryotic cells • amt of DNA in E. coli 500x length of the cell so it must be highly coiled & folded

  38. Binary Fission • DNA begins replication @ specific spot: origin of replication creating 2 pts of origin • 1 pt of origin moves to opposite end of cell • as DNA replicates cell elongates  ~2x • when DNA replication complete plasma membrane pinches in 2 • each new cell has exact same DNA as parent cell

  39. Binary Fission

  40. Binary Fission • unknowns: • how pts of origin move (no microtubules) • proteins similar to actin & tubulin identified

  41. Evolution of Mitosis • Some unicellular eukaryotes existing today have mechanisms of cell division that may resemble intermediate steps in the evolution of mitosis

  42. Dinoflagellates • chromosomes attach to nuclear envelope • nuclear envelope remains intact thru cell division • microtubules pass thru nucleus stabilizing chromosome positions • rest of cell division very like binary fission

  43. Dinoflagellates

  44. Diatoms & some Yeasts • unicellular • nuclear envelopes remain intact • spindle formed of microtubules inside nucleus • microtubules separate chromosomes • nucleus then splits

  45. Diatoms

  46. Controlling the Cell Cycle • different cell types divide at different rates • all controlled by regulation @ molecular level

  47. Cell Cycle Control System • a cyclically operating set of molecules in the cell that • trigger • coordinate • checkpoint: control pt where stop & go signals can regulate cell cycle

  48. Checkpoints: Animal Cells • have built-in stops that must be over-ridden by go signals • most come from mechanisms w/in cell • responsible for checking whether crucial processes that should have occurred by that pt. have been successfully completed • ckpts. also register signals from outside cell

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