cellular division chapter 18-19 cell division when? growth replacement of older cells production of specialized cells asexual reproduction sexual reproduction production of gametes prokaryotic binary fission eukaryotic cell cycle cell cycle interphase G1 S G2 checkpoints quality control proteins check progress cell cycle kinases MPF - maturation (mitosis) promoting factor two subunits kinase subunit regulatory subunit cyclin CDK - cyclin dependent kinases responsible for control of various aspects of cell cycle naming CDC (cell division cycle protein) - number or CDK - number cyclin number eg. B/CDK1
cell-cycle control cyclin concentration transcription - proteolysis major cyclin types - G1 - increase gradually throughout cell cycle G1/S - rise in late G1 then fall in S S - rise in S, remain high into early M M - rise in G2 peak at metaphase major checkpoints G1S checkpoint (restriction) checks DNA damage checks cell size prior to S phase DNA replication checkpoint checks maturation of replication complex G2M checkpoint checks DNA damage checks cell size prior to M phase metaphase checkpoint mitotic exit checkpoint checks completion of mitosis cell cycle kinases cyclin binding binds to catalytic subunit of CDK 4 steps used to control CDK activity cdk inhibitors control cell cycle progression, i.e. Sic1 phosphorylation/dephosphorylation CDK-activating kinase (CAK)- double phos. phosphatase removes one - activates CDK controlled proteolysis breaking down of cyclins and CDKs subcellular localization cyclins move between cytoplasm and nucleus checkpoints cell cycle progress can be stopped by sensors detect abnormalities transmitters signal the problem effectors inhibit cell cycle many proteins may be produced that arrest progress CHK1 - inhibits CDC25 p21 - inhibits G1 CDK p27 - inhibits S phase (inhibits cyca/cdk2)
prophase chromosome compaction topoisomerase II condensin - aids compaction cohesin - forms ring around sister DNA molecules nuclear envelope disperses golgi and ER fragment prophase centromeres kinetochores inner plate binds to centromere outer plate coronal fibers protrude from plate connect to microtubule by dynein and CENP-E (motor protein) binds to plus end of microtubule (NDC80 complex) prophase centrosome cycle centrioles duplicated centrosomes move apart from one another organize mitotic spindle asters prometaphase definitive mitotic spindle formed microtubules grow into region around chromosome searching motor proteins of kinetochore move chromosome to end of microtubule kinetochore attaches each chromatid attached opposite poles movement of chromosomes motor proteins of kinetochores lengthening & shortening of MTs
metaphase chromosomes aligned metaphase (equatorial) plate attached microtubules remain dynamic spindle fibers highly organized astral microtubules chromosomal microtubules polar microtubules anaphase sister chromatids split separase move apart depolymerization at - end provides force to move chromosomes anaphase A chromosomes move toward poles anaphase B two spindle poles move in opposite directions telophase final stage ends with return to interphase mitotic spindle disassembles nuclear envelopes reassemble chromosomes disperse cytoplasm partitioned cytokinesis division of cytoplasm cytokinesis indentation of cell surface cleavage furrow develops same plane as metaphase plate cytoplasmic vesicles fuse with furrow midbody abscission contractile ring theory actin filaments moved via myosin II bipolar myosin II
plant cells cytokinesis in plants cell plate phragmoplast remnant microtubules actin filaments vesicles meiosis Reduction devision in animals - used to produce gametes in plants - used to produce spores chromosomes - somatic cells - usually pairs gametes - usually single copy total number of homologs = N somatic cells are usually diploid (2N) gametes are usually haploid (1N) results in 4 daughter nuclei half the genetic material of the original 2 stages meiosis I meiosis I premeiotic S phase way longer than in mitosis prophase I leptotene zygotene synapsis centromere synaptonemal complex leptotene zygotene pachytene tetrad prophase I pachytene synapsis ends diplotene synaptonemal complex disappears homologous chromosomes start moving apart centromere synaptonemal complex leptotene zygotene pachytene tetrad chiasma chiasma diplotene diakinesis metaphase I diplotene diakinesis metaphase I
meiosis I meiosis I prophase I diakinesis chromosomes prepare for attachment to spindle fibers nuclear envelope disappears chiasma centromere synaptonemal complex leptotene zygotene pachytene diplotene diakinesis metaphase I tetrad metaphase I homologous chromosomes align held together by chiasmata anaphase I homologous chromosomes separate independent assortment telophase I nuclear envelope may reform interkinesis haploid number of chromosomes diploid amount of DNA 2 x 1N meiosis II metaphase II chromosomes align anaphase II sister chromatids separate migrate to poles products 4 haploid nuclei problems sometimes mistakes happen crossing over? nondisjunction aneuploidy mutations during DNA replication deletion duplication inversion translocation
life cycles variations in life cycle alternation of generation plants animals? gametic/terminal meiosis production of haploid gametes sporic/intermediate meiosis production of spores zygotic/initial meiosis diploid generation (2N) haploid generation (1N) gametes zygote (2N) meiosis sporophyte meiosis spores gametophyte meiosis end of line cellular death two types necrosis messy results from trauma programmed cell death cell volume decreases cellular blebbing apoptotic bodies, nuclear fragmentation cell swells lysis inflammation gametes (1N) amoebocyte engulfs bodies animal plant fungus characteristics of programmed cell death voluntary carefully orchestrated clean form of self defense extrinsic pathway death receptor for vertebrates - tumor necrosis factor receptors bind to death ligands death domains - bind to adaptor proteins (FADD) proteases - procaspase-8 caspase-8 death ligands death receptor death domains FADD procaspase-8 caspase-8 normal
procaspase cysteine aspartate-specific proteases (caspases) cell executioners three domains large and small catalytic domains prodomain three classes of caspases initiator caspases (caspase-8, -9) executioner caspases (caspase-3, -6, -7) inflammatory caspases inactive cleavage sites intrinsic pathway balance between pro- and anti- signals target bcl-2 proteins 3 groups BH3 small subunit prodomain large subunit active caspase BH4 BH3 BH1 BH2 TM antiapoptopic BH3 double inhibition Bcl-2 (4BH) inhibits Bak & Bax (3 BH) BH3only - inhibit the inhibitors -> activate BH1 BH2 TM apoptopic Bak or Bax -> form MOMP - channel - cytochrome C leak caspase amplification intrinsic pathway mitochondrial outer membrane permeabilization cytochrome c binds with APAF-1 apoptosome BH3 only antiapoptotic (4 BH domains) apoptotic (3 BH domains) Bak, Bax - form oligomers BH3 only amplifying APAF-1 procaspase-9 APOPTOSOME executioner procaspases executioner caspases caspase activity initiator caspases executioner caspases
stereotypical morphological changes condensation of chromatin cleavage of DNA into fragments nuclear fragmentation karyorrhexis blebbing phospholipid bilayer composition changes plasma membrane bulges organelles enclosed in plasma membrane fragments apoptotic bodies phagocytosis