Chapter 11: Eukaryotic Cell Cycle & Cell DivisionI. Eukaryotic Cell Cycle A. Diagram:1. Time is not shown here2. Cell moves clockwise through cycle, starting at G1B. Interphase (G1, S, G2)1. G1 usually longest phase – cells spend most of their life in G1a. If cell stays in G1 forever, it has exited the cycle and is in “G0” (“G not”)i. Can be turned on again b. Cells in G1 or G0 are normally functioning cells – doesn’t mean they’re dying 2. S: DNA Synthesis/Chromosome Replication (Fig. 11.4)3. G2: synthesize proteins for M phaseC. M (Mitosis)1. Mitosis : division of nuclear material (genetic material)2. Cytokinesis : Division of all other cellular materialD. Cell progression is controlled by cell signaling via Cyclin proteins1. Involved at three checkpoints (Fig. 11.17) a. End of G1 checkpoint: is there DNA damage?b. End of G2 checkpoint: is all the DNA replicated?c. Metaphase checkpoint: are chromosomes attached to the spindle?2. Cyclins & how they work (Fig. 11.14)a. Amounts and types of cyclins vary as cell cycle progressesb. Cyclins bind to & turn on cyclin-dependent kinases (CDK’s)c. CDK’s phosphorylate (activate) proteins needed to continue in cycled. Cyclins are degraded when cell moves to next stagee. Production of cyclin is the initial signal – must be turned off eventually (degraded)II. Eukaryotic Chromosome StructureSynthesis of DNASGap 2G2Gap 1G1MCytokinesisMitosis1 11 1Fig. 11.4Fig. 11.14Fig. 11.17A. Chromosomes (“colored bodies”)1. Units of genetic material; made of chromatin & contain genesa. Chromatin: mixture of protein (histones) & DNAi. Compacts DNAb. Genes: sequences of DNA that code for a product & the DNA regions that control production (start/stop codons, promoter, etc.)B. Structure (Fig. 11.4, pages 1 & 3)1. Eukaryotic chromosomes are linear a. Centromere: region of constriction i. Doesn’t have to be in the middle2. After chromosome replicationa. Pair of sister chromatids = 1 chromosome (even though you now have double the DNA)b. Kinetochore proteins lie over the centromere region – interact with microtubules & get pushed & pulled aroundC. Chromosomes occur in sets1. Haploid a. 1 copy of each type of chromosome (n)b. Gametes of diploid organisms are N (haploid)c. Haploid organisms produce gametes by mitosis, & autosomal cells and gametes areboth N2. Diploid a. 2 copies of each chromosome (2N)b. Autosomal (non-gametic) cells of diploid organisms are 2Nc. Gametes are N3. Some eukaryotes are tetraploids (4N)a. Ex. Durum wheat, green treefrogIII. Mitosis 1 21 1 2 2A. Forms 2 genetically identical daughter cellsB. *S-Phase occurs before any of mitosis (Fig. 11.4)C. 5 phases of Mitosis: PPMAT-I (Fig. 11.5)1. Prophase a. Chromosomes condenseb. Dark Blue = paternal copyc. Light Blue = maternal copy2. Prometaphase a. Nuclear membrane breaks downb. Spindle formsc. Microtubules attach to kinetochore proteins of chromosomes (Fig. 11.6)3. Metaphase a. Sister chromatids align on metaphaseplate4. Anaphase a. Sister chromatids separate & move topoles5. Telophase & cytokinesis a. Nuclear membrane reforms; daughtercells separate6. Interphase a. Chromosomes replicate (S). Requiredfor mitosis to occurIV. Meiosis Fig. 11.4Fig. 11.6Fig. 11.5A. “Reduction division”1. I.e. N daughter cell produced from 2N parent cell2. 2 rounds of division (Meiosis I & Meiosis II)3. Same steps as mitosis, done twice (Some differences)B. Unique to Meiosis I (Fig. 11.9)1. Homologous chromosomes, already duplicated, synapse (=pair) to form bivalents or tetrads2. Synapsed chromosomes exchange some material (“crossingover”)3. At the site of crossover the chromosomes form an “X” or chiasma4. In eukaryotes, ~1-60 crossovers occur per chromosome, permeiosisC. Meiosis I (Fig. 11.10) 1. 5 Phasesa. Prophase I (Fig. 11.8) – tetrads form, crossing overb. Prometaphase I – bivalents attach to microtubulesc. Metaphase I – bivalents randomly align on plated. Anaphase I – homologous chromosomes move to separate polese. Telophase I – haploid daughter cells separate2. Meiosis I is reduction division – 2 haploid cells from 1 diploid3. 2 processes increase genetic diversity in Meiosis Ia. Crossing over (prophase I)b. Random alignment of chromosomes on metaphase plate (metaphase I)D. Meiosis II (Fig. 11.11)Fig. 11.9Fig. 11.10 – Meiosis I Fig. 11.8 – Prophase I1. Prophase II – no tetrads or crossing over2. Prometaphase II – sister chromatids attach to microtubules3. Metaphase II – sister chromatids align on plate4. Anaphase II – sister chromatids separate; chromosomes move to separate poles5. Telophase II – cleavage: 4 haploid cells producedV. Mitosis vs. Meiosis EVENT Mitosis Meiosis I Meiosis IITetrads form: No Yes YesCrossing over occurs: No Yes NoWhat aligns on metaphase plate:Sister chromatids Tetrads/bivalents Sister chromatidsWhat is produced: 2 cells, diploid 2 cells, haploid, withsister chromatids4 cells, haploidReduction Division: No Yes
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