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Transcript
Cell Division Cell division • Biology is the only subject in which multiplication is the same as division Where it all began … • You started as a cell smaller than a period at the end of a sentence … And now look at you … How did you get from there to here? Going from there to here … • Going from egg to baby … • The original fertilized egg has to divide .. and divide … and divide … and divide … Why do cells divide? • For reproduction • Asexual reproduction • One-celled organisms • For growth • From fertilized egg to multicellular organism • For repair & renewal • Replace cells that die from normal wear & tear or from injury Needed to make new cells • Nucleus • Chromosomes • DNA • Cytoskeleton • Centrioles • Animal cells only • Microtubule spindle fibers DNA Nucleus chromosome • Function • Protects DNA histone protein • Structure • Nuclear envelope • Double membrane • Membrane fused in spots to create pores • Allows large macromolecules to pass through What kind of molecules need to pass through? nuclear pores nucleolus nuclear pore nuclear envelope Cytoskeleton • Function • Structural support • Maintains shape of cell • Provides anchorage for organelles • Protein fibers • Microfilaments, intermediate filaments, microtubules • Motility • Cell locomotion • Cilia, flagella, etc • Regulation • Organizes structures & activities in cell Cytoskeleton actin microtubule nuclei Centrioles • Cell division • In animal cells, pair of centrioles organize microtubules • Spindle fibers • Guide chromosomes in mitosis Centrioles Getting what you need • What is passed on to daughter cells? • exact copy of genetic material = DNA • Mitosis • Organelles, cytoplasm, cell membrane, enzymes • Cytokinesis chromosomes (stained orange) in kangaroo rat epithelial cell notice cytoskeleton fibers Overview of mitosis interphase I.P.M.A.T. prophase (pro-metaphase) cytokinesis metaphase anaphase telophase M Mitosis G2 Gap 2 Cell cycle • Cells have a “life cycle” cell is formed from a mitotic division cell grows & matures to divide again G1, S, G2, M epithelial cells, blood cells, stem cells S Synthesis cell grows & matures to never divide again liver cells G1G0 brain / nerve cells muscle cells G1 Gap 1 G0 Resting Interphase • 90% of cell life cycle • Cell doing its “everyday job” • Produce RNA, synthesize proteins/enzymes • Prepares for duplication if triggered Time to divide & multiply! I’m working here! Interphase • Divided into 3 phases: • G1 = 1st Gap (Growth) • Cell doing its “everyday job” • Cell grows • S = DNA Synthesis • Copies chromosomes • G2 = 2nd Gap (Growth) • Prepares for division • Cell grows (more) • Produces organelles, proteins, membranes G0 Interphase • Nucleus is well-defined • DNA loosely packed in long chromatin fibers • Prepares for mitosis • Replicates chromosomes • DNA & proteins • Produces proteins & organelles S phase: copying DNA • Synthesis phase of Interphase • Dividing cell replicates DNA • Must separate DNA copies correctly to 2 daughter cells • Human cell duplicates ~3 meters DNA • Each daughter cell gets complete identical copy • Error rate = ~1 per 100 million bases • 3 billion base pairs in mammalian genome • ~30 errors per cell cycle (mutations) ACTGGTCAGGCAATGTC DNA Organizing DNA • DNA is organized into chromosomes histones • Double helix DNA molecule • Wrapped around histone proteins • Like thread on spools • DNA-protein complex = chromatin • Organized into long thin fiber chromatin • Condensed during mitosis double stranded chromosome duplicated mitotic chromosome Copying DNA & packaging it • After DNA duplication, chromatin condenses • Coiling & folding make it a smaller package DNA chromatin mitotic chromosome double-stranded mitotic human chromosomes Chromosome vocabulary • Duplicated chromosome • 2 sister chromatids • Narrow at centromere • Contain identical copies of original DNA homologous chromosomes single-stranded homologous chromosomes sister chromatids double-stranded homologous = “same information” Mitosis • Dividing cells DNA between 2 daughter nuclei • 4 phases • Prophase • Metaphase • Anaphase • Telophase Prophase • Chromatin condenses • Becomes visible chromosomes • Centrioles move to opposite poles of the cell • Animal cells only • Protein fibers cross cell to form mitotic spindle • Microtubules (actin, myosin) • Coordinate movement of chromosomes • Nucleolus disappears • Nuclear membrane breaks down Transition to Metaphase • Prometaphase • Spindle fibers attach to centromeres • Creating kinetochores • Chromosomes begin to move Metaphase • Chromosomes align along middle of cell • Metaphase plate • Meta = middle • Spindle fibers coordinate movement • Helps to ensure chromosomes will separate properly • So each new nucleus receives only 1 copy of each chromosome Anaphase • Sister chromatids separate at kinetochores • Move to opposite poles • Pulled at centromeres • Pulled by motor proteins along microtubules • Actin, myosin • Increased production of ATP • Poles move farther apart • Polar microtubules lengthen Separation of chromatids • In anaphase, proteins holding together sister chromatids are inactivated • Separate to become individual chromosomes 1 chromosome 2 chromatids double-stranded 2 chromosomes single-stranded Chromosome movement • Kinetochores use motor proteins that “walk” chromosome along attached microtubule • Microtubule shortens by dismantling at kinetochore (chromosome) end Telophase • Chromosomes arrive at opposite poles • Daughter nuclei form • Nucleoli form • Chromosomes uncoil • No longer visible under a light microscope • Spindle fibers disappear • Cytokinesis begins • Cell division Cytokinesis in animal cells • Constriction of actin microfilaments around equator of cell • Cleavage furrow forms • Splits cell in two Cytokinesis in animal cells (play Cells Alive movies here) (play Thinkwell movies here) Mitosis in whitefish blastula Mitosis in animal cells Cytokinesis in plant cells • Cell plate forms • Vesicles line up at equator • Derived from Golgi • Vesicles fuse to form 2 cell membranes • New cell wall develops between membranes • New cell wall fuses with existing cell wall Cytokinesis in plant cells Mitosis in plant cells onion root tip Any Questions??