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D.N.A Objective: SWBAT identify the cell cycle as a source of cell division and cell regulation. When an individual falls down and cuts themselves, explain how the wound is able to heal itself?. D.N.A Objective: SWBAT identify the cell cycle as a source of cell division and cell regulation.
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D.N.AObjective: SWBAT identify the cell cycle as a source of cell division and cell regulation • When an individual falls down and cuts themselves, explain how the wound is able to heal itself?
D.N.AObjective: SWBAT identify the cell cycle as a source of cell division and cell regulation • 1. There are a number of differences between fission of a bacterium and human cell division. Which of the following are NOT one of the them? • A. A bacterium has only one chromosome • B. Human cells undergo mitosis and cytokinesis • C. Bacteria are smaller and simpler than human cells • D. Bacteria have to duplicate their DNA before dividing; human cells do not • E. Human chromosomes are larger and more complex. • Which of the following correctly matches a phase of the cell cycle with its description A. M – replication of DNA B. S – immediately precedes cell division C. G2 – cell division D. G1 – immediately follows cell division E. Above are all correctly matched
Where it all began… You started as a cell smaller than a period at the end of a sentence…
Cell Division • “Omnis cellula e cellula” – Virchow • “all cells from cells” • Cells reproduce to form genetically identical daughter cells
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? • _Reproduction________ • Asexual reproduction • one-celled organisms • _For growth__________ • from fertilized egg to multi-celled organism • _Repair and renewel • replace cells that die from normal wear & tear or from injury amoeba
Prokaryotic Cell Division • Binary Fission: • Steps in Binary Fission • Bacterial DNA is duplicated • Cell grows • Cell splits in two
Eukaryotic Cell Division • The Cell Cycle • Interphase • G1, S, and G2 phases • Mitotic Phase • Mitosis • Cytokinesis
Interphase • The cell spends __90%____of its time in interphase • G1: • “Gap 1” • Cell growth • S: • “Synthesis” • DNA is replicated • G2: • “Gap 2” • Cell growth • Preparation for division
green = key features Interphase • Nucleus well-defined • DNA loosely packed in long chromatin fibers • Prepares for mitosis • replicates chromosome • DNA & proteins • produces proteins & organelles
I.P.M.A.T. Overview of mitosis interphase prophase (pro-metaphase) cytokinesis metaphase anaphase telophase
Don’t Forget!! • DNA in eukaryotes are packed into things called chromosomes!
homologous chromosomes homologous chromosomes sister chromatids Mitotic Chromosome • Duplicated chromosome • 2 sister chromatids • narrow at centromeres • contain identical copies of original DNA single-stranded homologous = “same information” double-stranded
green = key features Prophase (DNA is Packaged!) • Chromatin condenses • visible chromosomes • Chromatids • Protein fibers cross cell to form mitotic spindle • coordinates movement of chromosomes • Nucleolus disappears • Nuclear membrane breaks down
green = key features Transition to Metaphase • Prometaphase • spindle fibersattach to centromeres • chromosomes begin moving
green = key features Metaphase (Middle) • 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
green = key features Anaphase (AHHHHH!) • Sister chromatids separate at kinetochores • move to opposite poles • pulled at centromeres
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
green = key features Telophase (Becomes 2!) • Chromosomes arrive at opposite poles • daughter nuclei form • nucleoli form • chromosomes disperse • no longer visible under light microscope • Cytokinesis begins • 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
Cytokinesis • Division of the cytoplasm • Animal Cells: • Cleavage furrow forms • Pinches the cell into two • Plant Cells: • Cell plate forms • Divides the cell in 2
What does Mitosis make at the end? Mitosis makes two identical cells, each with its own copy of the DNA These cells are sometimes called “daughter cells”
Coordination of cell division • A multicellular organism needs to coordinate cell division across different tissues & organs • critical for normal growth, development & maintenance • coordinate timing of cell division • coordinate rates of cell division • not all cells can have the same cell cycle
M anaphase metaphase telophase prophase C G2 interphase (G1, S, G2 phases) mitosis (M) cytokinesis (C) G1 S Frequency of cell division • Frequency of cell division varies by cell type • embryo • cell cycle < 20 minute • skin cells • divide frequently throughout life • 12-24 hours cycle • liver cells • retain ability to divide, but keep it in reserve • divide once every year or two • mature nerve cells & muscle cells • do not divide at all after maturity • permanently in G0
sister chromatids centromere single-stranded chromosomes double-stranded chromosomes There’s noturning back, now! Overview of Cell Cycle Control • Two irreversible points in cell cycle • replication of genetic material • separation of sister chromatids • Checkpoints • process is assessed & possibly halted • internal and external signals
Checkpoint control system • Checkpoints • cell cycle controlled by STOP & GO chemical signals at critical points • signals indicate if key cellular processes have been completed correctly
Checkpoint control system • 3 major checkpoints: • G1/S • can DNA synthesis begin? • G2/M • has DNA synthesis been completed correctly? • commitment to mitosis • spindle checkpoint • are all chromosomes attached to spindle? • can sister chromatids separate correctly?
G1/S checkpoint • G1/S checkpoint is most critical • primary decision point • “restriction point” • 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
G0 phase • G0 phase • non-dividing, differentiated state • most human cells in G0 phase • liver cells • in G0, but can be “called back” to cell cycle by external cues • nerve & muscle cells • highly specialized • arrested in G0 & can never divide
Activation of cell division • How do cells know when to divide? • cell communication signals • chemical signals in cytoplasm give cue • signals usually mean proteins • activators • inhibitors experimental evidence: Can you explain this?
“Go-ahead” signals • Protein signals that promote cell growth & division • internal signals • “promoting factors” (MPF) • external signals • “growth factors” (PDGF) • Primary mechanism of control • phosphorylation • kinase enzymes • either activates or inactivates cell signals
External signals • Platelet-derived growth-factor (PDGF) stimulates cell division to heal injuries • coordination between cells • protein signals released by body cells that stimulate other cells to divide • density-dependent inhibition • crowded cells stop dividing • each cell binds a bit of growth factor • not enough activator left to trigger division in any one cell • anchorage dependence • to divide cells must be attached to a substrate • “touch sensor” receptors
Cancer & Cell Growth • Cancer is essentially a failure of cell division control • unrestrained, uncontrolled cell growth • What control is lost? • lose checkpoint stops • gene p53 plays a key role in G1/S restriction point • p53 protein halts cell division if it detects damaged DNA • options: • ALL cancers have to shut down p53 activity p53 is theCell CycleEnforcer p53 discovered at Stony Brook by Dr. Arnold Levine
What causes these “hits”? • Mutations in cells can be triggered by • UV radiation • chemical exposure • radiation exposure • heat • cigarette smoke • pollution • age • genetics
Tumors • Mass of abnormal cells • Benign tumor • abnormal cells remain at original site as a lump • p53 has halted cell divisions • most do not cause serious problems &can be removed by surgery • Malignant tumor • cells leave original site • lose attachment to nearby cells • carried by blood & lymph system to other tissues • start more tumors =metastasis • impair functions of organs throughout body
Traditional treatments for cancers • Treatments target rapidly dividing cells • high-energy radiation • kills rapidly dividing cells • chemotherapy • stop DNA replication • stop mitosis & cytokinesis • stop blood vessel growth
New “miracle drugs” • Drugs targeting proteins (enzymes) found only in cancer cells • Gleevec • treatment for adult leukemia (CML)& stomach cancer (GIST) • 1st successful drug targeting only cancer cells withoutGleevec withGleevec Novartes