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Transcript
The Cell Cycle: Cell Growth, Cell 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? Why do cells divide? • Reproduction – asexual reproduction • one-celled organisms • Growth and Development – from fertilized egg to multi-celled organism • Repair and Replacement – replace cells that die from normal wear & tear or from injury amoeba Cell Cycle M Mitosis Cell cycle G2 Gap 2 • Cell has 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 I’m working here! Time to divide & multiply! Interphase • Divided into 3 phases: – G1 = 1st Gap • cell doing its “everyday job” • cell grows • A few hours to indefinitely – S = DNA Synthesis • copies chromosomes • 3-6 hours – G2 = 2nd Gap • prepares for division • cell grows (more) • produces organelles, proteins, membranes • 2-5 hours G0 green = key features Interphase • Longest phase of the cell cycle – Consists of G1, S, G2 • Cell prepares for mitosis – replicates chromosome • DNA & proteins – produces proteins & organelles ACTGGTCAGGCAATGTC Organizing DNA • DNA is organized in Nucleosomes DNA histones – double helix DNA molecule – wrapped around Histones • like thread on spools – DNA-protein complex = Chromatin • organized into long thin fiber chromatin – condensed further during mitosis double stranded chromosome duplicated mitotic chromosome Copying DNA & packaging it… • After DNA duplication, chromatin condenses – coiling & folding to make a smaller package mitotic chromosome DNA chromatin doublestranded mitotic human chromosomes Mitotic Chromosome • Duplicated chromosome – 2 chromatids – narrow at centromere – contain identical copies of original DNA homologous chromosomes homologous chromosomes single-stranded sister chromatids double-stranded homologous = “same information” Mitosis • Dividing cell’s DNA between 2 daughter nuclei – “dance of the chromosomes” • 4 phases – Prophase – Metaphase – Anaphase – Telophase Mitosis Overview of mitosis interphase prophase I.P.M.A.T. (pro-metaphase) cytokinesis metaphase anaphase telophase green = key features Prophase • Chromatin condenses – Becomes 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 green = key features Transition to Metaphase • Prometaphase – Special proteins attach to the centromeres • creating kinetochores – microtubules attach at kinetochores • connect centromeres to centrioles – Nuclear envelope fragments green = key features Anaphase • Sister chromatids separate – 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 green = key features Telophase • Chromosomes arrive at opposite poles – Nuclear envelop starts to reappear – nucleoli form – Chromosomes uncoil • no longer visible under light microscope • Spindle fibers disperse • Cytokinesis – cell division Cytokinesis • Animals – constriction belt of actin microfilaments around equator of cell • cleavage furrow forms • splits cell in two • like tightening a draw string Mitosis in whitefish blastula Cytokinesis in Plants • Plants – Cell Plate • 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 Cytokinesis in plant cell onion root tip G1/S checkpoint • G1/S checkpoint is most critical – primary decision point • “Go Ahead signal” – if cell receives “GO” signal, it divides • internal signals: cell growth (size), cell nutrition • external signals: “growth factors” – if cell does not receive signal, it exits cycle & switches to G0 phase • non-dividing, working state What about Stem cells? • What are stem cells? • How can they be used? • What are concerns about using stem cells? • What are the types of stem cells? Multicellular organisms depend on interactions among different cell types. CELL TISSUE leaf stem vascular tissue ORGAN lateral roots primary root shoot system SYSTEMS root system • Tissues are groups of cells that perform a similar function. • Organs are groups of tissues that perform a specific or related function. • Organ systems are groups of organs that carry out similar functions. Specialized cells perform specific functions. • Cells develop into their mature forms through the process of cell differentiation. • Cells differ because different combinations of genes are expressed. • A cell’s location in an embryo helps determine how it will differentiate. Outer: skin cells Middle: bone cells Inner: intestines Stem cells can develop into different cell types. • Stem cells have the ability to – divide and renew themselves – remain undifferentiated in form – develop into a variety of specialized cell types • Stem cells are classified into three types. – totipotent, or growing into any other cell type – pluripotent, or growing into any cell type but a totipotent cell – multipotent, or growing into cells of a closely related cell family • Stem cells come from adults and embryos. – Adult stem cells can be hard to isolate and grow. – The use of adult stem cells may prevent transplant rejection. – The use of embryonic stem cells raises ethical issues. – Embryonic stem cells are pluripotent and can be grown indefinitely in culture. First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules. • The use of stem cells offers many current and potential benefits. – Stem cells are used to treat leukemia and lymphoma. – Stem cells may cure disease or replace damaged organs. – Stem cells & Blindness – Stem cells may revolutionize the drug development process.