Essential Cell Biology Cell Cycle & Apoptosis PDF

Alberts Johnson Lewis Raff Roberts Walter Essential Cell Biology Fourth Edition Chapter 18 The Cell Cycle + Apoptosis tutor: Jan van Weering Copyright © Garland Science 2008 The cell cycle  Learning...

Alberts Johnson Lewis Raff Roberts Walter Essential Cell Biology Fourth Edition Chapter 18 The Cell Cycle + Apoptosis tutor: Jan van Weering Copyright © Garland Science 2008 The cell cycle  Learning objectives cell cycle and apoptosis You.... can name the different phases of the cell cycle and explain the role cyclin/Cdks. can name the checkpoints of the cell cycle, explain why they are important and how they work. know how chromosomes are split in cell division. can explain why apoptosis is important and how it is prevented in healthy cells. Ted-talk by Hans Clevers http://youtu.be/oMEihKffBJI Why do cells divide? Wound healing  Why do cells divide? Organ maintenance. The complete gut epithelium is replaced every 4 days. How do cells divide? Diploid daughter cells are formed by mitosis Chromosomes Chromosomes Chromosomes n=2 n=4 n=2  Meiosis & Mitosis N=2 N=2 N=4 N=4 N=2 N=4 N=1 N=2  The cell cycle M-phase: mitosis + cytokinesis only 5% of the total G2-phase: cell cell cycle time growth, condensate chromosomes, check internal/external factors. G1-phase: cell growth, new organelles, S-phase: DNA- transcription and synthesis; duplication translation. of chromosomes G0-phase: cell in rest. The S-phase: DNA duplication original copy chromosome chromosome The M-phase comprises 5 mitosis-phases and cytokinesis: separate daughter chromosomes and daughter cells  The M-phase: Cell division 1072 PANEL 17–1: The Principle Stages of M Phase (Mitosis and Cytokinesis) in an Animal Cell 1 PROPHASE At prophase, the replicated centrosome chromosomes, each intact consisting of two closely forming nuclear mitotic associated sister chromatids, envelope spindle condense. Outside the nucleus, the mitotic spindle assembles between the two centrosomes, which have replicated and moved apart. For simplicity, only three chromosomes are shown. In diploid cells, there would be kinetochore two copies of each chromo- some present. In the photo- condensing replicated chromosome, consisting of micrograph, chromosomes two sister chromatids held together along their length are stained orange and microtubules are green. netochore tworeplicated copies ofand moved each apart. chromo- For present. some simplicity,In only thethree photo- The M-phase: Cell division condensing replicated chromosome, consisting of chromosomes are shown. In micrograph, chromosomes two sister chromatids held together along their length diploid cells, there would be kinetochore aretwo stained of eachand copiesorange chromo- microtubules some present.areIngreen. the photo- condensing replicated chromosome, consisting of micrograph, chromosomes two sister chromatids held together along their length are stained orange and microtubules are green. 2 PROMETAPHASE Prometaphase starts 2 PROMETAPHASE abruptly with the fragments of Prometaphase starts centrosome nuclear envelope breakdown of the nuclear abruptly with the at spindle fragments of envelope. Chromosomes pole centrosome nuclear envelope breakdown of the nuclear at spindle canenvelope. now attach to spindle Chromosomes pole microtubules via their can now attach to spindle kinetochores microtubulesand via undergo their kinetochores active movement.and undergo active movement. kinetochore chromosome in active motion kinetochore chromosome in active motion microtubule microtubule  The M-phase: Cell division kinetochore chromosome in active motion microtubule 3 METAPHASE centrosome at spindle pole At metaphase, the chromosomes are aligned at the equator of the spindle, midway between the spindle poles. The kinetochore microtubules attach sister chromatids to opposite poles of the spindle. kinetochore microtubule  The M-phase: Cell division 4 ANAPHASE daughter chromosomes At anaphase, the sister chromatids synchronously separate to form two daughter chromosomes, and each is pulled slowly toward the spindle pole it faces. The kinetochore microtubules get shorter, and the spindle poles also move apart; both processes contribute to chromosome segregation. shortening kinetochore spindle pole microtubule moving outward  move apart; both microtubules get shorter, processes and contribute the spindle polestoalso chromosome segregation. shortening kinetochore The M-phase: Cell division spindle pole move apart; both processes contribute to microtubule chromosome segregation. shortening moving outward kinetochore spindle pole microtubule moving outward 5 TELOPHASE During telophase, the two 5 TELOPHASE sets of telophase, During daughter chromo- the two set of daughter chromosomes somes sets arrive at the of daughter poles of chromo- at spindle set of daughter pole chromosomes the spindle somes arriveand decondense. at the poles of at spindle polecontractile ring A new the nuclear spindle and envelope decondense. starting to ring contractile A new nucleararound reassembles envelopeeach contract starting to contract reassembles set, completing around each the formation set, completing of two the marking nuclei and formation of thetwo endnuclei and marking of mitosis. The the end of mitosis. The division of the cytoplasm division of the cytoplasm begins with contraction of begins with contraction of the contractile the contractilering. ring. overlap centrosome centrosome overlap microtubules microtubules nuclear nuclear envelope reassembling envelope reassembling around around individual chromosomes chromosomes  starting to contract reassembles of two around eachmarking nuclei and set, completing the formation the end of mitosis. The of two nuclei and marking The M-phase: Cell division division of the cytoplasm the end of mitosis. The begins with contraction of division of the cytoplasm the contractile ring. begins with contraction of the contractile ring. centrosome overlap microtubules nuclear envelope reassembling centrosome overlap around individual chromosomes microtubules nuclear envelope reassembling around individual chromosomes 6 CYTOKINESIS 6 CYTOKINESIS During cytokinesis, the Duringcytoplasm completed nuclear envelope is the cytokinesis, divided in two by ais surrounds decondensing cytoplasm contractile divided inring two of completed nuclear envelope chromosomes actin andring by a contractile myosin of surrounds decondensing filaments, actin and myosin which pinches chromosomes the cell filaments, in two which to create pinches the celltwo daughters, in two to createeach with one nucleus. two daughters, each with one nucleus. contractile ring re-formation of interphase creating contractile ringcleavage array of of interphase microtubules nucleated re-formation furrow creating cleavage array ofby the centrosome microtubules nucleated furrow by the centrosome (Micrographs courtesy of Julie Canman and Ted S (Micrographs courtesy of Julie Canman and Ted Salmon.) Cell cycle checkpoints The checkpoints are regulated by cyclins and cyclin- dependent kinases (Cdks).  Cyclin activity is ended by De concentratie M-cyclines (en activiteit) wordt ubiquitination and degradation of the cyclin. gereguleerd l d door d eiwit degradatie d d 18 07 cyclin degradat jpg 18_07_cyclin_degradat.jpg Aan het eind van de mitose bindt ubiquitin aan M-cycline, waardoor het afgebroken wordt door het proteasoom Evolutionary conservation of cyclin/Cdk complexes Checkpoints are regulated by cyclins. The discovery of cyclins synchronous cell division Synchronous cell division in a zebra sh embryo model fi The discovery of cyclins  Initiation of the cell cycle Check 1: Check 2: Check 3: Start? DNA OK? Can chromosomes be split? Activation of G1-Cdk by mitogens and the MAP kinase pathway......and active G1-Cdk initiates S-phase gene transcription.  Checkpoints are regulated by cyclins. Check 1: Check 2: Check 3: Start? DNA OK? Can chromosomes be split? Checkpoints are regulated by cyclins.  Summary 1: overview of the cell cycle The cell cycle produces daughter cells, essential for wound healing and organ maintenance. 4 phases: G(ap)1, S(ynthesis), G(ap)2 & M(itosis) G1: cell growth, transcription & translation, new organelles S: duplication of the DNA G2: condensation of chromosomes, cell growth M: separation of chromosomes and daughter cells 3 checkpoints: G1-S: external factors OK for cell division and is the DNA undamaged? G2-M: Is the DNA duplicated correctly? M metaphase-anaphase: Are the chromosomes correctly attached to the microtubules? The cell cycle checkpoints are regulated by cyclin/Cdks. G1-phase: prepare DNA for duplication by preRC S-phase: pre-RC to preinitiation complex switch, which triggers DNA polymerase. S-phase: duplication of chromosomes At the end of mitosis, the ORC is dephosphorylated, making the chromosome available for another round of the cell cycle.  Mitosis: the separation of chromosomes. chromosomes are split over daughter cells by interaction with microtubules  G2/M checkpoint: M-cyclin M-cyclin has several diverse functions that trigger mitosis, one of which is the expression of Survivin that is critical to form the microtubule spindles. Duplication of the centrioles precedes spindle formation. Centrioles are duplicated already during the S-phase, and migrate to opposite sides of the nucleus under control of M-Cdk.  Organisation of the centrioles –1: The Principle Stages of M Phase (Mitosis and Cytokinesis) in an Animal Cell Prophase centrosome At prophase, the replicated chromosomes, each consisting of two closely forming mitotic associated sister chromatids, spindle condense. Outside the nucleus, the mitotic spindle assembles between the two centrosomes, which have replicated and moved apart. For simplicity, only three chromosomes are shown. In diploid cells, there would be two copies of each chromo- some present. In the photo- d chromosome, consisting of micrograph, chromosomes held together along their length are stained orange and microtubules are green. Prometaphase: attach the duplicated chromosome to the microtubules of the spindle by kinetochore  Metaphase: microtubules align the chromosomes at the midline se, the mes are aligned tor of the dway between poles. The e microtubules r chromatids to oles of the Metafase: pulling force on chromosomes by kinetochore microtubules  Metaphase: microtubules align the chromosomes at the midline Kinesins move to the +end of microtubules Anaphase: separation of the duplicated chromosomes metafase anafase  Chromosomes are separated by 2 types of microtubule movement. 3rd checkpoint: are all chromosomes attached to the spindles? Attachment of sister chromatids by the cohesin complex Separation of daughter chromosomes by APC/C original copy original copy chromosome chromosome chromosome chromosome M-Cdk active APC/C active separase cohesin break-down cyclin break-down: end of mitosis cohesin Metaphase-anaphase checkpoint APC/C is an E3-ligase: ubiquitin ligase for proteins, especially cyclins.  Metaphase-anaphase checkpoint Cdc-20-APC/C interaction is blocked when kinetochore is not associated to the chromosomes.  De resets APC/C concentratie M-cyclines all cyclins (en activiteit) by triggering wordt cyclin degradation. gereguleerd l d door d eiwit degradatie d d 18 07 cyclin degradat jpg 18_07_cyclin_degradat.jpg Aan het eind van de mitose bindt ubiquitin aan M-cycline, waardoor het APC/C is an E3-ligase: ubiquitin ligase afgebroken wordt door het proteasoom for proteins, especially cyclins. Nuclear envelope is formed in the telophase  Not only the DNA, but also all organelles need to be split over the newly formed daughter cells: Golgi  Not only the DNA, but also all organelles need to be split over the newly formed daughter cells: Mitochondria  Cytokinesis: separation of daughter cells Cytokinesis is triggered by the dephosphorylation of Cdks and cyclin breakdown by APC/ C ubiquitination. Organelles are divided over the daughter cells. The midbody is the nal contact between the two daughter cells. fi Samengevat: functie cytoskelet tijdens M-fase The critical cytoskeletal laments in mitosis Mitose: Mitosis: Cytokinese: Cytokinesis: Microtubuli microtubles Actine Actin/myosin fi  Summary 2: mechanism of cell division S/Cdk activates DNA duplication: helicase & DNA polymerase bind the DNA helix. In mitosis, the duplicated chromosomes are split over the daughter cells by interaction with microtubules. Centrioles are duplicated and form two microtubule spindles, triggered by M/Cdk. Chromosomes bind to the spindle microtubules through kinetochore. Chromosomes are organised by kinesin motor proteins to the midline. Chromosomes are divided over the daughter cells upon break-down of cohesin, triggered by the APC/C complex. The APC/C triggers also the break-down of all cyclins, thereby ending mitosis. In cytokinesis, the daughter cells are split by the contractile ring formed by actin and myosin.  The cell cycle M-phase: mitosis + cytokinesis only 5% of the total G2-phase: cell cell cycle time growth, condensate chromosomes, check internal/external factors. G1-phase: cell growth, new organelles, S-phase: DNA- transcription and synthesis; duplication translation. of chromosomes G0-phase: cell in rest.  Factors that control cell division Mitogens: these activate a new wave of G1/S-Cdk activity to drive the cell to the S-phase. Growth factors: these stimulate protein synthesis and cell growth. Some growth factors prevent programmed cell death (e.g. neurotrophic factors), and are essential for cell survival. DNA damage blocks cell division DNA activates p53 and p21 transcription...... DNA damage blocks cell division...and p21 translation produces a protein that inhibits Cdk.  Mutations in p53 are a risk factor for cancer uncontrolled cell division = cells divide on the wrong location at the wrong time. cancer can be a consequence of uncontrolled cell division, e.g. upon deactivation of the p53 system. Cell apoptosis = programmed cell death Apoptosis Necrosis  Hallmarks of apoptosis Extracellular: Cell loses its shape and shrinks. The plasma membrane forms protrusions (“blebs”). Cell debris is recognised by macrophages that clear the cell remnants. Intracellular: The nuclear envelope disintegrates and chromatin is degraded. Degradative vacuoles are formed. Irreversible caspase activation that mediate protein degradation. Disassembly of the cytoskeleton. Degradation of mitochondria and release of cytochrome C. Apoptosis is essential for tissue maintenance and development. development of a mouse paw The tail of a tadpole is removed by apoptosis. Syndactyly patients have a defect in apoptosis. Activation of the caspase cascade in apoptose “The kiss of death” Bcl-2 prevents cytochrome C release from mitochondria.......and cytochrome C can activate caspase 9 to induce the caspase cascade. Survival factors block apoptosis. Inhibitor of apoptosis like Bcl2  balancing cell division and apoptose programmed cell division and death: Controlled by internal and external factors. Defect in cell division regulation or apoptosis: Various diseases including cancers and Syndactyly.  Summary 3: Apoptosis & Cell cycle Apoptosis is programmed and controlled cell death, this is a normal process in cell function and tissue maintenance. Apoptosis is triggered by the release of cytochrome C to the cytosol, which triggers the caspase cascade. Apoptosis is prevented in healthy cells by IAP (Inhibitors of Apoptosis) like Bcl-2. Survival factors can prevent apoptosis through several signalling cascades.  Learning objectives cell cycle and apoptosis You.... can name the different phases of the cell cycle and explain the role cyclin/Cdks. can name the checkpoints of the cell cycle, explain why they are important and how they work. know how chromosomes are split in cell division. can explain why apoptosis is important and how it is prevented in healthy cells.