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The Cell Cycle

The Cell Cycle. Imagine your skin…. Cells have a life cycle. It goes from birth…to birth…to birth…to birth… Is there death? Eventually… Cells (most human cells at least) are limited in the number of times they can reproduce.

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The Cell Cycle

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  1. The Cell Cycle

  2. Imagine your skin…

  3. Cells have a life cycle • It goes from birth…to birth…to birth…to birth… • Is there death? • Eventually… • Cells (most human cells at least) are limited in the number of times they can reproduce. • Infant skin cells placed in a Petri dish may reproduce 100 or more times • A 60 year old’s skin cells may only reproduce about 20 times.

  4. So what’s in between each “birth” event? • Life. • The cell carries out it’s life functions. It does its job. • The life cycle of a cell… from birth to life to birth is called the CELL CYCLE.

  5. By Convention… • We normally talk about INTERPHASE as the stage that marks the “beginning of the cell cycle.

  6. INTERPHASE • The stage of a cell’s life in which the cell is doing one of two things: • Living out its life and doing its job • Preparing for cell division – the “birth” of two new cells

  7. Interphase Time to get ready to make new cells! • 90% of cell life cycle • cell doing its “everyday job” • prepares for duplication if triggered I’m working here! Time to make new Cells!

  8. Cell cycle • Cell has a “life cycle” cell is formed from a mitotic division cell grows & matures to divide again cell grows & matures to never divide again G1, S, G2, M liver cells G1G0 epithelial cells,blood cells, stem cells brain / nerve cells muscle cells

  9. G0 signal to divide Interphase • Divided into 3 phases: • G1= 1stGap (Growth) • cell doing its “everyday job” • cell grows • S= DNA Synthesis • copies chromosomes • G2 = 2ndGap (Growth) • prepares for division • cell grows (more) • produces organelles,proteins, membranes

  10. Control of Cell Cycle

  11. Understanding Chromosome Structure and Terminology • During G1

  12. Understanding Chromosome Structure and Terminology • During S

  13. Understanding Chromosome Structure and Terminology • During G2

  14. MITOSIS • NOW we are ready to “give birth” to new cells! • We have replicated the genetic material • We now need to “divvy up” one complete set of genes to each cell that will be “born” • THIS is mitosis – the division of the nucleus

  15. Mitosis • Dividing cell’s DNA (chromosomes) between 2 daughter nuclei • 4 phases • prophase • metaphase • anaphase • telophase

  16. Why do cells divide by MITOSIS? • For reproduction • asexual reproduction • one-celled organisms • For growth • from fertilized egg to multi-celled organism • For repair & renewal • replace cells that die from normal wear & tear or from injury GOAL of MITOSIS = DAUGHTER CELLS that are IDENTICAL to the PARENT CELLS!! amoeba CLONES!!!

  17. Cytoskeleton Fibers • Fibers that support the cell as well as move things around in the cell • VERY IMPORTANT in the events of MITOSIS • THEY MOVE THE CHROMOSOMES! • THEY CUT THE CELL IN TWO!

  18. Cytoskeletal Fibers • Made of PROTEIN • 3 Types • Intermediate Filaments • Microfilaments • Microtubules

  19. Intermediate filaments • No real role in mitosis • More permanent • Made of Keratin family of proteins • Support • Fix position of organelles • When shape is important

  20. Microfilaments • Solid rods • Made of actin protein • Bear tension (pulling forces) • Support and change cell shape – 3D network just inside cell membrane • Responsible for Cleavage furrow in cell division (actin interacting w/ myosin – much like in muscle cell)

  21. Microtubules • Straight hollow rods • Made of tubulin – a protein • Microtubules elongate by adding tubulin molecules to the ends of the tube • Can be disassembled and reassembled elsewhere • Provide: • Shape; support • “tracks” • guide secretory vesicles to plasma membrane • Separation of chromosomes during cell division

  22. Microtubules and Cell Division • Centrosomes • Centrioles • May help organize spindle • Animal cells only • Spindle Fibers

  23. I.P.M.A.T. Overview of the Cell Cycle interphase prophase (pro-metaphase) cytokinesis metaphase anaphase telophase

  24. green = key features Prophase • Chromatin condenses • visible chromosomes • chromatids • Centrioles move to opposite poles of cell • animal cell • Protein fibers cross cell to form mitotic spindle • microtubules • actin, myosin • coordinates movement of chromosomes • Nucleolus disappears • Nuclear membrane breaks down

  25. green = key features Transition to Metaphase • Prometaphase • spindle fibersattach to centromeres • creating kinetochores • microtubules attach at kinetochores • connect centromeres to centrioles • chromosomes begin moving

  26. Kinetochore • Each chromatid has own kinetochore proteins • microtubules attach to kinetochore proteins

  27. double-strandedmitotic humanchromosomes

  28. green = key features Metaphase • Chromosomes align along middle of cell • metaphase plate • meta = middle • spindle fibers coordinate movement • helps to ensure chromosomes separate properly • so each new nucleus receives only 1 copy of each chromosome

  29. green = key features Anaphase • Sister chromatids separate at kinetochores • move to opposite poles • pulled at centromeres • pulled by motor proteins “walking”along microtubules • actin, myosin • increased production of ATP by mitochondria • Poles move farther apart • polar microtubules lengthen

  30. Separation of chromatids • In anaphase, proteins holding together sister chromatids are inactivated • separate to become individual chromosomes 1 chromosome 2 chromatids 2 chromosomes single-stranded double-stranded

  31. green = key features Telophase • Chromosomes arrive at opposite poles • daughter nuclei form • nucleoli form • chromosomes disperse • no longer visible under light microscope • Spindle fibers disperse • Cytokinesis begins • cell division

  32. Cytokinesis in Animals Link

  33. Mitosis in whitefish blastula

  34. Cytokinesis in Plants • Plants • cell plate forms • vesicles line up at equator • derived from Golgi • vesicles fuse to form 2 cell membranes • new cell wall laid down between membranes • new cell wall fuses with existing cell wall

  35. Mitosis in plant cell

  36. onion root tip

  37. Origin of replication chromosome: double-stranded DNA replication of DNA elongation of cell ring of proteins cell pinches in two Evolution of mitosis • Mitosis in eukaryotes likely evolved from binary fission in bacteria • single circular chromosome • no membrane-bound organelles

  38. prokaryotes (bacteria) Evolution of mitosis • A possible progression of mechanisms intermediate between binary fission & mitosis seen in modern organisms protistsdinoflagellates protistsdiatoms eukaryotes yeast eukaryotes animals

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