Chapter12.pdf BIOLOGY 108 - 0001
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AP Biology 20122013 Unit 5 Chapter 12 The Cell Cycle 121 Cell Division Cell Cycle life of a cell from when it39s formed from a parent cell until its own division into two daughter cells Somatic Cells all body cells except the reproductive cells in humans contain 46 chromosomes 23 inherited from each parent Gamets reproductive sperm and egg cells contain 23 chromosomes in humans of chromosomes varies with species Genome a cell39s genetic information DNA Chromosomes structures in which DNA molecules are manageably packaged each chromosome consists of one DNA molecule and many proteins Chromatin building material of chromosomes Uncoiled in thin chromatin fiber when cell is not dividing Condense into chromosome structures when cell begins to divide Sister Chromatids each chromosome has two when separating joined copies of original chromosome attached by sister chromatid cohesion sisters will eventually separate and become their own chromosomes Centromere each sister has one region containing specific DNA sequences where sisters are attached Sides of centromere Chomosome Arms quotquot7 397 1 Sister 4111 27777 7111 V gt chmmatids r AAAK if A A A A A A A AA Chromosome Repl icaliion Centromere j Chromosome Chromosome replication Mitosis division of genetic material in the nucleus Cytokinesis division of the cytoplasm 122 Mitotic Phase and Interphase Mitotic Phase includes both mitosis and cytokinesis Interphase accounts for 90 of the cell division cycle cell grows and copies chromosomes to prepare for division Three Phases of Interphase G1 First Gap Phase Cell Growth 56 Hours S Phase Copy of Chromosomes 1012 Hours G2 Second Gap Phase More Cell Growth 46 Hours M Mitotic Phase Cell Divides 1 Hour 5 DNA synthesis Stages of Mitosis G2 of Interphase single centrosome has duplicated itself Prophase chromatin condense into discrete chromosomes nucleoli disappear duplicated chromosomes appear sister chromatids joined at centromeres mitotic spindle begins to form centrosomes move away from one another lengthening microtubules Prometaphase nuclear envelope fragments microtubules extending from centrosomes invade nuclear area chromosomes more condensed each chromatid has a kinetochore specialized protein at centromere kinetochore microtubules jerk chromosome back and forth Metaphase centrosomes at opposite sides of cell chromosomes convene at metaphase plate equidistant between spindle poles kinetochores of sister chromatids attach to kinetochore microtubules from opposite poles Anaphase sister chromatids break apart chromatid is now a chromosome liberated daughter chromosomes move to opposite ends of cell cell elongates as microtubules lengthen Telophase two daughter nuclei form in the cell and nuclear envelopes arise nucleoli reappear chromosomes become less condensed remaining spindle microtubules depolymerized mitosis complete Cytokinesis division of cytoplasm underway at the end of telophase cleavage furrow pinches cell in two Mitotic Spindle forms in cytoplasm during prophase constructed of centrosome with microtubules branching off of it Centrosome organizes the cell39s microtubules starts construction on spindle Aster short microtubules extending from each centrosome Kinetochore structure of proteins associated with specific sections of DNA at each centromere present in each sister chromatids spindle microtubules will quotcapturequot kinetochores making them kinetochore microtubules quottug of warquot between two kinetochore microtubules in opposite directions NonKinetochore Microtubules elongate expanding the cell Metaphase Plate imaginary structure midway between spindle39s poles on which centromares of duplicated chromosomes lie Aster Mitotic center cemgrosome iPolar Cntr iole pair am i crotubul e Kinetochore Cytokinesis In Animal Cells Cleavage Furrow shallow groove in cell surface near metaphase plate contraction of actin microfilaments deepen furrow until cells are separated Cytokinesis in Plant Cells Cell Plate vesicles derived from Golgi carrying cell wall materials coalesce plate expands until it reaches the membrane on perimeter of cell creating two separate cells the cell plate becoming a new cell wall Binary Fission reproduction of singlecell eukaryotes ex amoeba cell doubles in size then splits in half Prokaryotic Replication More difficult than eukaryotic due to SUPER long chromosomes in comparison to size of cell chromosomes must be coiled VERY tightly Chromosomes begin replication at two origins as cell elongates Plasma membrane pinches inward dividing into two daughter cells 12 3 Eukaryotic Cell Cycle Cell Cycle Control System set of molecules in a cell that triggers and coordinates key events in the cycle Checkpoints cycle is regulated by these internal and external signals at these points the cycle will be given the quotgoaheadquot or the quotstopquot signal animal cells stop at checkpoints until overridden by a quotgoaheadquot signal signals come from surveillance mechanisms inside the cell Three Major Checkpoints G1 G2 and M Gl quotRestriction Pointquot most important if given goahead cell will most likely proceed through all other checkpoints if not given quotgoaheadquot at Gl cycle will stop switching into nondividing state of G0 most cells of human body are in G0 state Regulatory Cell Cycle Proteins Protein Kinases activate or inactivate other proteins buy phosphorylating them usually always present in a cell but inactive Cyclin must be attached to a kinase for it to be active CyclinDependent Kinases Cdks Activity of Cdks uctuates with change in concentration of cyclin Cyclin level rises in S and G2 phases and falls during M phase MPF maturationpromoting factor triggers cell39s passage past G2 checkpoint into M phase MPF complex consists of Cdk molecule and cyclin acts directly as kinase and indirectly by activating other kinases MPF turns itself off in anaphase by destroying its cyclin CI Degraded a cyclin e Internal and External Signals at Checkpoints Internal Example sister chromatids will not separate until all are properly attached to spindle External Example cell will not divide if an essential nutrient is lacking Growth Factor protein released by certain cells that stimulates other cells to divide DensityDependent Inhibition effect of external physical factor on cell division crowded cells stop dividing even wit growth factors Anchorage Dependence to divide cells must be attached to a substratum extracellular matrix communicated to cell through cytoskeleton Cancer Cells Neither density or anchorage dependent will just keep dividing When they stop dividing they do so at random points in cell cycle not at checkpoints Evade triggers for cell to undergo apoptosis cell death when something is wrong Unusual numbers of chromosomes Lose attachments to neighboring cellsextracellular matrix allowing for movement Transformation conversion of normal cell to cancer cell usually recognized and destroyed if not destroyed cell will proliferate and form tumor mass Benign Tumor mass of abnormal cells with not enough genetic and cellular changes to survive at another site stays where it39s at Malignant Tumor includes cells that can spread to new tissues and impair function of other organs Metastatis spread of cancer cells from their original site once transformed cell breaks off of tumor and enters bloodlymph vessels Chapter 13 Meiosis and Sexual Life Cycles 131 Genes Gametes reproductive cells that transmit genes from one generation to the next sperm and egg cells 23 chromosomes each Locus a gene39s specific location along a chromosome Asexual Reproduction single individual passes copies of all its genes to its offspring no fusion of gametes offspring is exact replica of parent clones unless mutation occurs Sexual Reproduction two parents give rise to offspring that have a unique combination of genes from each parent not exact replicas 132 Fertilization and Meiosis Karyotype ordered display of chromosomes arranged in pairs starting with the longest Homologous Chromosomes two chromosomes of same length and centromere position but holding information one chromosome of each pair from each parent Sex Chomosomes X and Y chromosomes determine gender Human Females XX Human Males XY Autosomes all other chromosomes Diploid cell with two chromosome sets both sets of 23 from each parent making 46 Haploid cell with one set of chromosomes 23 sex cells 22 autosomes and 1 sex chromosome Egg contains X chromosome Sperm can contain X or Y chromosome Zygote resulting of an egg fertilized by a sperm mitosis of zygote generates all somatic cells of the body only cells not generated by mitosis gametes developed from specialized germ cells in gonads ovaries for women and testes for men Meiosis gamete version of cell division 1 Egg or sperm haploid 2 Fertilization creates a diploid 3 Meiosis reduces number of chromosome sets from 2 to 1 to restore haploid Alternation of Generations life cycle exhibited by plants and some algae Sporophyte multicellular diploid stage during which meiosis occurs creating haploid spores Spore divides generating a multicellular haploid stage gametophyte Cells of gametophyte give rise to gametes Haploid gametes fuse and create a diploid zygote then on to next sporophyte generation Sporophyte generation produces gametophyte Gametophyte generation produces sporophyte THEY ALTERNATE Animal Life Cycle Alternation of Generations Fungi and Protist Plants and Algae Life Cycle Two haploid gametes fuse to Sporophyte divides generating Gametes fuse forming diploid create a diploid zygote multicellular gametophyte zygote Mitosis occurs giving rise to Gametophyte cells give rise to gametes Meiosis occurs no multicellular diploid multicellular Haploid gametes fuse and create diploid diploid develops organism zygote Produces haploid cells that divide by Meiosis occurs returning Sporophyte generation produces mitosis and give rise to unicellular cells to haploid gametes gametophyte descendents or a haploid adult Gametophyte generation produces organism sporophyte Either haploid or diploid cells can undergo mitosis Only diploid cells can undergo meiosis 133 Meiosis Meiosis I and Meiosis II two consecutive cell divisions resulting in four daughter cells each daughter cell has half as many chromosomes as parent cell Prophase I Synapsis homologs become physically connected to each other Crossing Over genetic rearrangement between nonsister chromatids Chiasmata exists at point where crossover has occurred Spindle formation and nuclear envelope breakdown Metaphase I Pairs of homologous chromosomes arrange at metaphase plate Homologs are attached to spindle fibers at kinetochores Anaphase I Homologs separate whereas SISTER CHROMATIDS REMAIN ATTACHED Homologs move toward opposite poles Telophase I and Cytokinesis Each half of the cell has complete haploid set of duplicated chromosomes Two haploid daughter cells are formed through furrowing Prophase II Spindle forms individually in each cell Metaphase II Chromosomes positioned at metaphase plate Kinetochores attach to spindle fibers Anaphase II Centromere breaks and sister chromatids are separated Spindle fibers pull chromatids towards opposite poles Telophase II and Cytokinesis Nuclei form in individual cells Four daughter cells each with an unduplicated haploid set of chromosomes are formed Each cell is genetically distinct from the other Meiosis I i ii E H i ii 33 l BWEWWMES Chiarimata Milerotuhule Sister eh mma39idie anaehedito M t mh remainla agihed tfi l Spindle Hinetoehoi e Film mire Palm Ehmimmlm Stator Tetraii osmiamri Hammad quot lamHelium ghrgmmaitiits with Hilnetnehm e chromosomes separate Homologous Ehmmesomes Fhil39r m s t u quot Tatianas no runs Pairs of homologous duplicate Pair l h Ghmmnsnmaa SEEI IWHM p llirt up Syria psis pairing of homologe to form tetrad Gleamagn furrow Si it ir ehtmmat ids Haploid daugm r Farm cells tom1mg h j l i eons I g fr fm Ewing mama Il39 iun 39 l eat division than sisiai ciimiiiaiiiis iiiiaiiiy 39 39 39 generate four haploid daughter celll s result containing sith chromosomal Con l mm E malm Im Mmmwasl a min cms Panam can Bhi asma site of quotEmma 3 before chromome mp lim m eraMing mar 39 Fmphasa 39 H39I ii Froli asel g a chiomosomallv Bhromoaosma 39 f quot q replication K ieminmlan 39 Tigtraldfgfmg by Duplieatiid cahmmosome 39 i 216 symapelsMhnmuluguue Ma slam chmat idsl 1 39 ehmmema Mmaphasse Metaphaea Chromosomes TaitEda i I39 39 39 positioned attrmi positionedaunt I J Wheamale mmmp haaeplme I a 1 J I V3 t K 7 7 i Anaphase quot Sister chromde Humni guea I L 27 39 Anaip39hiimll Telephaae gamma unrir lg swam Temptiqu mm lmquot mil I i I39Mquot Hap lu a one me E If 39 v x r ennuinaming V x o l II E39 l ramalntagether D i h r I j 2quot if rili fuolsl 35 ii 3 W 2n 2n i MEIDEISS Ill Daughter malls ofmliosls f if quot 22 w n 1quot 3931 quotiiquot a quot n Daughter calla of malus s It Sister chmmamids separate during anaphaae Ill Mitosis Meiosis Meiosis I Reductional Division Meiosis II Equational Division DNA replication occurs during interphase One division occurs resulting in two daughter cells No synapsis or crossing over Creates identical diploid daughter cells Allows for growth development and repair DNA replication occurs before only Meiosis I Two divisions occur resulting in four daughter cells Synapsis and crossing over occur between nonsister chromatids resulting in chiasmata held pairs Creates haploid differentiated daughter cells Produces gametes Halves number of chromosomes sister chromatid cohesion and crossing over work together to allow sister chromatids to stay together until anaphase II 134 Genetic Variation Random Orientation of Chromosomes Depending on which side of a homolog is closer to a given pole determines whether daughter cell inherits maternal or paternal chromosome 5050 Chance Since homologs arrange themselves independently this causes great variation Number of Possible Combinations 2quotn n being haploid number 84 million possibilities for humans Crossing Over Recombinant Chromosomes individual chromosomes that carry DNA derived from two parents Occurs in Prophase I DNA of nonsister chromatids is broken corresponding points and the two segments are joined a piece of maternal DNA is binded to paternal DNA 13 cross overs in each human human chromosome Random Fertilization