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Unformatted text preview: Chapter 6- Bacterial chromatin (e. coli) is a closed covalent circle, packaged into condensed nucleoprotein complex (nucleoid) o insulated loops a nick does not affect entire DNA DNA probably fixed to proteins in a way that prevents free rotation supercoiled loops o SMC proteins organize and compact DNA (4fold) Hinge-mediated dimerization 2 SMCs bend so N- & C-terminals together form head domain and 2 SMCs form hinge intermolecularly Eukaryotes: histones bact:SMC Amphipatic helix, heptad repeat, coiled coils - Animal somatic cells have homologs (2 versions of each chromosome 2n), 1 from mom, 1 from dad o interphase DNA, RNA, protein, molecular synthesis (growth/rest phase) euchromatin predominant during interphase, less condensed, actively transcribed heterochromatin more condensed, not actively transcribed G1 (active protein, lipid, carb synthesis) S (DNA rep, histone syn) G2- Mitosis: 2 identical daughter cells o Prophase visible chromosomes (sister chromatids), nucleolus disappears, nuclear membrane disassembles, spindle formation o Metaphase spindle attach to kinetochore (at centromere), metaphase plate o Anaphase centromere divides, sister chromatids move to opposite poles o Telophase spindle disappears, nuclear membranes form, nucleoli reform, chromosomes decondense, 2 identical daughter cells- Germ cells: haploid, # chromosomes - Meiosis o Prophase I: chromosomes condense and form homologous pairs, synapsis for crossing over, nucleolus disappears, nuclear membrane disassembles o Metaphase I spindles on either side attach to homologous pairs, metaphase plate o Anaphase I homologous pairs separate & move to opposite poles (n) o Telophase I 2 new spindle replace single spindles, no DNA rep b/t meiosis I/ II o Prophase II chromosomes start to move to midpoints of new spindles o Metaphase II metaphase plate o Anaphase II centromeres divide, chromatids move to opposite poles o Telephase II chromosomes decondense, nuclear membranes form, 4 haploids- Polytene chromosomes: replicate DNA, cells dont divide - Cytogenetics: study of chromosomes, during mitotic metaphase o Karyotype: arranging chromosomes in decreasing order of size P arm: short, q arm: long Humans have 22 pairs of autosomes and 1 pair of sex chromosomes Induce cell division w/ a mitogen, culture cells, arrest in metaphase w/ mitotic spindle inhibitor (drug blocking microtubule assembly) Aneuploidy: having more/less than normal diploid # of chromosomes Translocation: part of 1 chromosomes joined to some other chromosome Philadelphia chromosome (reciprocal translocation b/t chrom. 9 & 22) altered abl gene activates constitutively (all the time) chronic myelogenos leukemia Important for genes to have specific addresses in chromatin/chromosomes- FISH: DNA probe w/ attached fluorescent dye will bind to specific DNA sequence w/in denatured chromosome (detect aneuploidy, chromosomal...
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