BSC2010 Week 6 Notes
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Date Created: 02/12/16
BSC 2010 Week 6 Lecture Notes Dr . Baer Monday, February 18, 2016 Genetics Genetics o “The stuff of and study of heredity” o Related individuals resemble each other more than do individuals chosen at random o Within populations: identical twins resemble each other more than they resemble others because they share genetic material o Among populations: Zulus vs Laplanders o Among higher taxa: who’s more alike? Chimp and human or human and sea anemone? Why do related individuals resemble each other? o They share genes o Share environments o Language is an inherited trait Chapter 7 A. Reproduction: Problems to be solved a. Transfer of information i. Between parent and daughter cells ii. Between parent and offspring in multicellular organisms b. Apportionment of biological materials (organelles) B. Types of reproduction a. Asexual “clonal” reproduction i. Offspring are genetically identical to the parent ii. All prokaryotes, many eukaryotes iii. Occurs by binary fission in prokaryotes, mitosis in eukaryotes 1. Binary fission: DNA is replicated and results in 2 genetically similar daughter cells b. Sexual reproduction i. 2 parents combine genes in a stereotypical way ii. leads to recombination, offspring are genetically different from either parent iii. only occurs in prokaryotes C. Phases of the Eukaryotic Cell Cycle a. Interphase i. G1 1. Growth period of cell 2. Genes are being expressed, cell is growing 3. Each chromosome has a single, unreplicated double strand of DNA 4. One chromosome from each parent (male,female) forms a homologous pair aka homologs 5. Chromosomes iin nucleus, surrounded by nuclear membrane 6. 23 pairs of homologous chromosomes (46 chromosomes total) 7. cell has single centrosome ii. S phase 1. 1 double strand of DNA to 1 double strands of DNA 2. After DNA replication, 2 “sister chromatids” are present for each homolog 3. Each sister chromatid is the same double-stranded DNA molecule 4. 2 sister chromatids attached by proteins 5. centrosomes duplicate iii. G2 phase 1. Gets ready for mitosis iv. M Phase 1. Where mitosis occurs 2. Early prophase a. Chromosomes condense b. Mitoic spindle forms from centrosome c. Centrosomes begin to migrate to poles of cell d. Nucleoli disappear 3. mid prophase a. chromosomes fully condensed b. centrosomes complete migration to the poles c. nuclear envelope begins to degrade d. spindle fibers enter nuclear area from the pole e. kinetochores form at centromeres 4. prometaphase a. nuclear envelope completely degraded b. spindle fibers begin to attach at kinetochores c. sister chromatids attached to opposite poles 5. metaphase a. spindle fibers attached to centromere at kinetochore b. all sister chromatids attached to opposite poles c. chromosomes migrate to center plane of cell, “metaphase plate” 6. anaphase a. sister chromatids separate, migrate toward opposite poles b. poles move farther apart as non-kinetochore spindle fibers lengthen 7. Telophase a. Non-kinetochore spindle fibers continue to elongate cell b. Nuclear envelopes begin to form at poles c. Chromosomes de-condense back into chromatin d. Nucleoli re-form, cytokinesis begins D. Eukaryotic cell cycle control a. Cell replication must be under precise control b. If unicellular organisms had no control over reproduction, they would exhaust their resources and starve to death i. Signals from external environment c. In multicell organisms, cell reproduction must be controlled for proper development i. Internal signals, growth factors Friday, February 12, 2016 Cell Cycle Control If any parts are disrupted, cell goes through apoptosis CDKs act on cell-cycle regulators (cyclin dependent kinases) o Cell cycle regulator + ATP –CDK cell cy Reg-P + ADP o Signaling molecule cyclin synthesis CDK activation cell cycle progression o Cyclin is degraded by proteases Example; G1-S checkpoing qRb (retinoblastoma protein) is a cell-cycle inhibitor o Rb + ATP Rb-P + ADP Which is not a feature of cell cycle control? o None of the above Sexual Life Cycles 46 chromosomes 22 homologous pairs of autosomes o same length o same centromere o same sequence o same set of genes sequence homology: not all the same One pair of sex chromosomes o Females XX, males XY o Only small region of sequence homology Meiosis A. Function a. Mitosis is to faithfully replicate the parental genome in each daughter cell with no change in information content b. Proximate function of meiosis is to produce haploid cells from diploid cells c. Ultimate function of meiosis is to generate genetic variation upon which natural selection can act B. Sexual life cycles: diplontic (animals) a. Free living stage is diploid b. Gametes formed by meiosis c. Haploid gametes merge genomes to form diploid zygote (syngamy) C. Alternation of Generations a. Diploid sporophyte forms haploid spores by meiosis b. Spores form gametophyte by mitosis c. Gametophyte forms gametes by mitosis d. Gametes merge to form diploid zygote D. Haplotonic (fungi) a. Free living-multicellular orgaism b. Gametes formed by mitosis c. Gametes merge to form diploid zygote d. Zygote undergoes meiosis to form haploid cells E. Overview of Meiosis a. Interphase 1: G1 Phase i. Begin with 2 homologous chromosomes (out of n homologous pairs) ii. DNA content = 2C iii. Ploidy = 2n (diploid) b. Interphase 1: S Phase i. Chromosomes replicate ii. DNA content = 4C 1. But still diploid iii. Ploidy = 2n c. Meiosis I i. Homologus chromosomes separate ii. Cell division #1 iii. Results in two haploid (ploidy = n) cells with 2 sister chromatids of one of the two homologs d. Meiosis II i. Sister chromatids separate ii. Cell division #2 iii. Result is 4 haploid daughter cells, each with single unreplicated chromosome iv. Each cell contains one member of each homologous pair of chromosomes F. Meiosis I (more in depth) a. Early prophase I i. Homologous chromosomes pair ii. Synaptonemal complex (proteins) attaches homologs iii. “synapsis” iv. homologs form tetrads b. Late prophase II i. Chromosomes cross over, form “chiasmata” ii. Exchange DNA between homologs occurs at chiasma iii. Spindles form and attach to kinetochores as in mitosis c. Metaphase I i. Chromsomes lined up on metaphase plate in homologous pairs ii. Spindles from one pole attach to one chromosome of each pair iii. Spindles from the other chromosome of the pair d. Anaphase I i. Homologous chromosomes separate and move along spindle fibers toward pole ii. Sister chromatids remain attached at centromeres iii. Recombination has occurred e. Telophase and cytokinesis i. Homologous chromosomes reach opposite poles ii. Each pole ahs complete haploid complement of chromosomes iii. Each chromosome consists of two sister chromatids G. Meiosis II a. Prophase II i. Chromosomes move toward metaphase plate b. Metaphase II i. Chromosomes reach metaphase plate, as in mitosis ii. Kinetochores of sister chromatids attach to spindle fibers from opp poles c. Anaphase II i. Centromeres of sister chromatids separate ii. Sister chromatids move toward opposite poles d. Telophase and cytokinesis i. Mechanism as before ii. 4 haploid daughter cells formed from each parent cell iii. some chromosomes are recombinant, some are not e. whats the point of getting a haploid cell instead of a diploid cell? i. When two come together, would have double chromosomes f. Feature of human gametes? i. Haploid ii. Carry 23 chromosomes iii. Female carry x chromosome, male carry y (but not all male carry y, half of them half x) H. Apoptosis – programmed cell death a. At certain points in development, cells are programmed to die b. Failure of apoptosis leads to development abnormalities c. Cells with irreparable DNA damage (can lead to cancer, abnormal development) also subjected to apoptosis d. “suicide proteins” (caspases) are always present in inactive form i. regulation is post-translational, not of transcription e. “death signal” = cell missed a checkpoint f. In C. elegans, apoptosis involves three main proteins: Ced-9, Ced-4, and Ced-3 (Ced = “cell death”) g. In the absence of a death signal, Ced-9 inhibits Ced-4 h. Ced-3 is inactive in the absence of active Ced-4 i. Upon receipt of death signal, Ced-9 is inactivated j. Ced-4 becomes activated upon inactivation of Ced-9 k. Ced-4 activates Ced-3 which is a protease l. Protein degradation initiates activation of other proteases, nucleases
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