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Cell Cycle

Cell Cycle. Cell Cycle. describes the life cycle of a cell differs fundamentally between prokaryotes & eukaryotes shares four features among all cell types reproductive signal DNA replication genome segregation cytokinesis produces a new individual or new parts. Prokaryotic Cell Cycle.

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Cell Cycle

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  1. Cell Cycle

  2. Cell Cycle • describes the life cycle of a cell • differs fundamentally between prokaryotes & eukaryotes • shares four features among all cell types • reproductive signal • DNA replication • genome segregation • cytokinesis • produces a new individual or new parts

  3. Prokaryotic Cell Cycle • one circular chromosome • packed on a protein frame in the nucleoid • anchored to the plasma membrane • chromosome replication yields two anchored circles • cell growth separates anchored circles • annular pinching separates daughter cells Binary Fission

  4. binary fissionin a bacteriumFigure 9.2

  5. chromosome numbers vary widelyTable 9.1

  6. Eukaryotic Cell Cycle • multiple linear chromosomes • wrapped on a protein frame • contained within the nucleus • replication yields two complete sets of chromosomes • mitosis segregates one set of chromosomes to each end of the cell • cytokinesis divides the cytoplasm to form two new cells

  7. Eukaryotic Cell Cycle • mitosis, cytokinesis (M phase) and interphase • interphase represents most of the cell cycle

  8. eukaryotic cell cycleFigure 9.3 growth & biosynthesis growth & biosynthesis

  9. Cell Cycle Decision Making • G1 => S transition & G2 => M transitions require signals • CDKs signal cell cycle transitions • Cyclin-Dependent Kinases • kinases phosphorylate target proteins • phosphorylation activates (some) proteins • Cyclins activate CDKs by allosteric binding • Cyclins cycle

  10. eukaryotic cell cycleregulationFigure 9.4 “Go!” “Don’t go!” “Go!” “Radiation damage! Don’t go!” “Go!” Replicate! “Okay, go!”

  11. external signals stimulate cell division • growth factors stimulate cell division • platelet-derived growth factor • wound healing • interleukins • immune system function • erythropoietin • red blood cell production • each provides information to the cell regarding the needs of the body

  12. Eukaryotic Chromosomes • chromsomes consist of chromatin • double stranded DNA • protein “spools” • chromatin is ~1/2 DNA & 1/2 protein • chromatin is highly organized • DNA wraps around histone proteins to form nucleosomes • during cell division, nucleosomes coil tightly to form highly-condensed chromatin

  13. organization of chromatinFigure 9.5

  14. organization of chromatinFigure 9.6

  15. Replication • during S phase • partially wound DNA is replicated to form two identical copies of each chromosome • two sister chromatids remain attached at the centromere • each chromosome enters M phase as two linked sister chromatids • mitosis separates the chromatids and distributes one to each daughter cell

  16. mitosis: chromatin & cytoskeletonFigure 9.8

  17. events of mitotic phases • Prophase • chromosomes condense • nucleolus disorganizes • spindle apparatus begins to organize • kinetochores forms

  18. mitosis: cartoon versionFigure 9.8

  19. Mitotic spindle apparatusFigure 9.7

  20. events of mitotic phases • Prometaphase • nuclear envelope is fragmented • spindle fibers bind kinetochores • chromosomes begin to migrate to equatorial plate

  21. events of mitotic phases • Metaphase • chromosomes are aligned at equatorial plate • Anaphase • sister chromatids separate • daughter chromosomes migrate to poles • Telophase • prophase is reversed

  22. Animal Cytokinesis PlantFigure 9.10

  23. Cytokinesis: Division of Cytoplasm • Animals • annular pinching by actin & myosin ring • Plants • deposition of cell plate by Golgi vesicles • Organelles are distributed to daughter cells ~randomly

  24. Modes of Reproduction • asexual reproduction • production of genetic clones through mitotic cell divisions • common among plants (vegetative propagation) and unicellular eukaryotes • eliminates costs & risks associated with sexual reproduction • offspring lack genetic variability

  25. Modes of Reproduction • sexual reproduction • offspring exhibit genetic variability • each bears a unique combination of parental genetic contributions • requires • meiosis - reduction of chromosome number from 2n (diploid) to 1n (haploid) • fertilization - combination of 1n parental contributions to produce 2n offspring

  26. Fungal/animal life cyclesFigure 9.12

  27. Modes of Reproduction • meiosis produces • gametes - animals, some protists • spores - fungi, plants, some protists • produce 1n adults • produce gametes • fertilization (gamete fusion) produces • zygotes • produce 2n adults and/or • undergo meiosis

  28. Modes of Reproduction • meiosis • two divisions • reduces 2n parent cell to 1n products • always produces 4 haploid products • begins with 4 homologous chromatids • recombination produces novel chromatids • phases resemble mitotic phases, except • meiosis I - homologs pair at prophase • meiosis I - homologs separate at anaphase

  29. Meiosis I: cartoon versionFigure 9.14

  30. Modes of Reproduction • meiosis I • prophase I • chromosomes condense, spindle forms • nuclear envelope fragments • homologs pair (synapsis) • crossing over

  31. crossing- over occurs during prophase IFigure 9.15 Figure 9.16

  32. Modes of Reproduction • meiosis I • metaphase I • homolog pairs align at equatorial plate • anaphase I • homologs separate to poles • telophase I • may or may not happen

  33. Modes of Reproduction • interkinesis • period between telophase I and prophase II • no replication occurs

  34. Modes of Reproduction • meiosis II • prophase II • reverses telophase I • metaphase II • chromosomes align at equatorial plate • anaphase II • sister chromatids separate to poles • telophase II • reverses prophase

  35. mitosis => identical daughters meiosis => variable daughters Figure 9.17

  36. nondisjunction at anaphase I of meiosisFigure 9.18

  37. Errors of Reproduction • meiotic errors may result in chromosomal disorders • aneuploidy - incorrect genetic complement • nondisjuction • translocation

  38. Errors of Reproduction • meiotic errors may result in chromosomal disorders • polyploidy • 3, 4, or more sets of chromosomes • can perform mitosis (reproduce asexually) • 1, 3,5, etc. cannot perform meiosis

  39. Cell Death • death by necrosis • damage, poison, starvation • death by apoptosis (programmed cell death) • discards un-needed or old cells • signals are common in many organisms • many cancers result from failed apoptosis

  40. apoptosis: programmed cell deathFigure 9.18

  41. cell death mechanismsTable 9.2

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