Biology is the only subject in which multiplication is the same thing as division 2007-2008 The Cell Cycle: Cell Growth, Cell Division 2007-2008 Where it all began You started as a cell smaller than a period at the end of a sentence 1
And now look at you How did you get from there to here? Getting 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 u asexual reproduction one-celled organisms For growth u from fertilized egg to multi-celled organism For repair & renewal u replace cells that die from normal wear & tear or from injury amoeba 2
Making new cells Nucleus u chromosomes u DNA Cytoskeleton u centrioles in animals u microtubule spindle fibers Centrioles Cell division u in animal cells, pair of centrioles organize microtubules spindle fibers u guide chromosomes in mitosis Getting the right stuff What is passed on to daughter cells? u exact copy of genetic material = DNA mitosis u organelles, cytoplasm, cell membrane, enzymes cytokinesis chromosomes (stained orange) in kangaroo rat epithelial cell notice cytoskeleton fibers 3
Overview of mitosis I.P.M.A.T. interphase prophase (pro-metaphase) cytokinesis metaphase anaphase telophase Interphase 90% of cell life cycle u cell doing its everyday job produce RNA, synthesize proteins/enzymes u prepares for duplication if triggered I m working here! Time to divide & multiply! Interphase Divided into 3 phases: u G 1 = 1 st Gap (Growth) cell doing its everyday job cell grows u S = DNA Synthesis copies chromosomes u G 2 = 2 nd Gap (Growth) prepares for division cell grows (more) produces organelles, proteins, membranes G 0 4
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 G 1, S, G 2, M liver cells G 1 G 0 epithelial cells, blood cells, stem cells brain / nerve cells muscle cells green = key features Interphase Nucleus well-defined u DNA loosely packed in long chromatin fibers Prepares for mitosis u replicates chromosome DNA & proteins u produces proteins & organelles S phase: Copying / Replicating DNA Synthesis phase of Interphase u dividing cell replicates DNA u 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 w 3 billion base pairs in mammalian genome w ~30 errors per cell cycle n mutations (to somatic (body) cells) 5
Organizing DNA DNA is organized in chromosomes u double helix DNA molecule u wrapped around histone proteins like thread on spools u DNA-protein complex = chromatin organized into long thin fiber u condensed further during mitosis double stranded chromosome duplicated mitotic chromosome ACTGGTCAGGCAATGTC DNA histones chromatin Copying DNA & packaging it After DNA duplication, chromatin condenses u coiling & folding to make a smaller package DNA mitotic chromosome chromatin Chromosome structure scaffold protein chromatin loop rosettes of chromatin loops chromosome DNA nucleosome histone DNA double helix 6
doublestranded mitotic human chromosomes Mitotic Chromosome Duplicated chromosome homologous chromosomes u 2 sister chromatids u narrow at centromeres u contain identical copies of original DNA homologous chromosomes single-stranded sister chromatids double-stranded homologous = same information Mitosis Dividing cell s DNA between 2 daughter nuclei u dance of the chromosomes 4 phases u prophase u metaphase u anaphase u telophase 7
Prophase Chromatin condenses u visible chromosomes chromatids Centrioles move to opposite poles of cell u animal cell Protein fibers cross cell to form mitotic spindle u u microtubules actin, myosin coordinates movement of chromosomes Nucleolus disappears Nuclear membrane breaks down green = key features Transition to Metaphase Prometaphase u spindle fibers attach to centromeres creating kinetochores u microtubules attach at kinetochores connect centromeres to centrioles u chromosomes begin moving green = key features Metaphase Chromosomes align along middle of cell u metaphase plate meta = middle u spindle fibers coordinate movement u helps to ensure chromosomes separate properly so each new nucleus receives only 1 copy of each chromosome green = key features 8
Anaphase Sister chromatids separate at kinetochores u move to opposite poles u pulled at centromeres u pulled by motor proteins walking along microtubules actin, myosin increased production of ATP by mitochondria Poles move farther apart u polar microtubules lengthen green = key features Separation of chromatids In anaphase, proteins holding together siste chromatids are inactivated u separate to become individual chromosomes 1 chromosome 2 chromatids double-stranded 2 chromosomes single-stranded 9
Chromosome movement Kinetochores use motor proteins that walk chromosome along attached microtubule u microtubule shortens by dismantling at kinetochore (chromosome) end Telophase Chromosomes arrive at opposite poles u daughter nuclei form u nucleoli form u chromosomes disperse no longer visible under light microscope Spindle fibers disperse Cytokinesis begins u cell division green = key features Cytokinesis Animals u constriction belt of actin microfilaments around equator of cell cleavage furrow forms splits cell in two like tightening a draw string 10
Cytokinesis in Animals (play Cells Alive movies here) (play Thinkwell movies here) Mitosis in whitefish blastula Mitosis in animal cells 11
Cytokinesis in Plants Plants u cell plate forms vesicles line up at equator w derived from Golgi vesicles fuse to form 2 cell membranes u new cell wall laid down between membranes new cell wall fuses with existing cell wall Cytokinesis in plant cell Mitosis in plant cell 12
onion root tip Evolution of mitosis Mitosis in eukaryotes likely evolved from binary fission in bacteria u single circular chromosome u no membranebound organelles Origin of replication chromosome: double-stranded replication DNA of DNA elongation of cell ring of proteins cell pinches in two Evolution of mitosis A possible progression of mechanisms intermediate between binary fission & mitosis seen in modern organisms prokaryotes (bacteria) protists dinoflagellates protists diatoms eukaryotes yeast eukaryotes animals 13