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Chapter 10 Vocabulary: Binary fission Mitosis Karyotype Haploid Diploid Homologous pair Sister chromatid Cell cycle Centromere Tumor suppressor gene Proto-oncogene Outline 10.1 Bacterial Cell Division Can exchange DNA (plasmids) but don’t have sexual reproduction Binary Fission Cell division is clonal End result is 2 identical cells DNA replicates Single circular chromosome Nucleoid region SMC proteins organize and condense DNA Bi-directional from origin of replication Cell divides via elongation and septum formation E. coli divide every 20 minutes 1241632641282565121024 24hrs would give 281,474,976,710,656 bacteria! (trillions!) They don’t take over because they use up all their own nutrients and pollute their area with waste. Plus bacteria are susceptible to viruses and seasonal shifts. 10.2 Eukaryotic chromosomes Humans have 46 chromosomes (23pairs) Monosomy – missing one Trisomy – extra one Chromatin – DNA (40%) and protein (60%) Condensed structure Nucleosome (DNA wrapped around histones) Solenoids (higher order coiling) Scaffold proteins (solenoids wind around scaffold protein) Karyotype allows visualization of chromosomes (can be used to detect gross abnormalities in chromosome number or structure) Haploid – one set Diploid – pairs of chromosomes Homologous pairs Same genes, but different alleles Same size, centromere location, etc Chromosome replication Copies held together by cohesin at centromere (sister chromatids) 10.3 Overview of Eukaryotic Cell Cycle Function: growth, repair and maintenance Interphase G1 S G2 Mitosis Cytokinesis G0 10.4 Interphase: Preparation for Mitosis G1 (Gap 1) - primary growth S – DNA synthesis Diploid number is duplicated. Copies held together by cohesin proteins at centromere Kinetochores proteins allow for attachment of microtubules at centromere G2 (Gap 2) – secondary growth Chromosomes begin to condense Centrioles replicate Also in gap phases: making preparations Organelles duplicate Enzymes synthesized Energy generated 10.5 M Phase: Chromosome Segregation and the Division of Cytoplasmic Contents Prophase Sister Chromatids condense Spindle forms from microtubules Asters brace centrioles Nuclear envelope breaks down Reabsorbed by ER Prometaphase Chromosomes attach to microtubules by kinetochore Sister chromatids orient themselves to face opposite sides Metaphase Chromosomes line up along the equator of the cell. Anaphase Sister chromatids separate Cohesin dissolves and chromosomes separate at centromere Chromosomes are pulled to opposite poles by shortening spindle fibers Spindle moves apart elongating cell Telophase Chromosomes reach opposite poles of the cell Undoing prophase Nuclear membranes reform Golgi and ER reform Spindle breaks down Chromosomes uncoil rRNA genes can be expressed Cytokinesis – Cytoplasmic division Animals (actin filaments form cleavage furrow) Plants (cell plate filled in with cellulose) Fungi and some protists perform mitosis within the nucleus 10.6 Control of Cell Cycle Checkpoints can advance, delay or block the cell cycle Respond to internal signals (nutritional state, condition of DNA) and external signals (toxins, growth factors) Cdk (cyclin dependent kinases) are stimulants for division (use phosphorylation) Growth factors are stimulants for division 3 major checkpoints: G1/S primary checkpoint G2/M Spindle Cancer – uncontrolled cell growth Tumor-suppressor genes (p53) Seek out DNA damage Repairable – delay cell cycle Irreparable – apoptosis Both copies of these genes must loose function to cause cancer Proto-oncogenes (PDGF, EGF receptors) Often related to growth factors (or some molecule in their pathway to activating cell division) If even one copy is mutated cell cycle can be turned on The processes of binary fission and the eukaryotic cell cycle are important. Students should be able to describe the events of the cell cycle. Videos work well since this is a dynamic process that is easier seen moving rather than in stills. Regulation is important also, but don’t worry too much about specific molecules and their specific interactions. The chapter 9 pathway material is a bit much in this chapter.
