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Final Exam Notes

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University of Guelph
BIOL 1090
Wright& Newmaster

BIOL*1090 FINAL STUDY NOTES Deoxyribonucleic Acid (DNA)  Polymer  Each subunit is a nucleotide comprised of : a phosphate group; a five carbon sugar; one of four cyclic nitrogenous bases;  Four Nucleotides of DNA Pyrimidine nucleotides 1) Deoxythymidine monophosphate, dMTP 2) Deoxycyidine monophosphate, dCMP Purine Nucleotides – 3) Deoxyadenosine monophosphate, dAMP 4) Deoxyguanosine monophosphate, dGMP -both types connected by phosphodiester bonds  Double-stranded and the strands are antiparallel  Strands are held together by hydrogen bonds between bases on opposing strands and by hydrophobic interactions between adjacent stacked bases  Strands are polar; 5’ end has a free phosphate group; 3’ end has a free hydroxyl group;  Two grooves of different width: major (bigger) minor (smaller)  Supercoiled > relaxed covalently closed DNA; relaxed, nicked circular DNA; negatively supercoiled, covalently closed DNA (chromosome)  Prokaryotic chromosome – highly compact – supercoiled ‘flower’  Bacterial, eukaryotic – similar – DNA found in mitochondria & chloroplasts – exist in circular chromosomes (resemble prokaryotic)  Eukaryotic chromosome – comprised of proteins, DNA, RNA Levels of Condensation 1. Packaging DNA as a negative supercoil into nucleosomes (linker DNA wrapped around nucleosome core – linker region is susceptible to digestion by enzyme endonuclease) DNA is wrapped around a nucleosome core of 8 histone proteins and anchored by a 9 th 2. An additional folding or supercoiling of the 11nm fibre to produce a 30nm fibre; driven by nucleosomal interactions; histone H1 involved; models: solenoid & zigzag; 30nm fibre is the basic structure unit of the metaphase chromosome (DNA in its most condensed form); 3. Attachment of the 30nm fibre at many positions to a (non-histone) protein scaffold (2-nm DNA molecule > 11nm nucleosomes > 30nm chromatin fiber > metaphase chromosome Telomeres  Protect chromosome ends  Resists degradation by DNases  Prevent fusion of chromosomal ends  Facilitate replication of the ends of the linear DNA Centromeres  Provide the point of attachment of chromosomes to microtubules in the mitotic spindle (spindle-fiber microtubule = glue)  Yeast centromeres – three essential regions  In multicellular eukaryotes are larger & more complex Transcription  Nucleus  RNA polymerase moves the transcription bubble, a stretch of unpaired nucleotides, by breaking the hydrogen bonds between complementary nucleotides. (Splits DNA)  RNA polymerase adds matching RNA nucleotides that are paired with complementary DNA bases. (Copies)  RNA sugar-phosphate backbone forms with assistance from RNA polymerase. (Prints)  Hydrogen bonds of the untwisted RNA+DNA helix break, freeing the newly synthesized RNA strand. (Releases)  If the cell has a nucleus, the RNA is further processed (addition of a 3' poly-A tail and a 5' cap) and exits through to the cytoplasm through the nuclear pore complex. (Into cytoplasm)  Read 3’ > 5’, created 5’ > 3’  RNA uses the pyrimidine URACIL instead of THYMINE Translation  Cytoplasm  Messenger RNA (mRNA) produced by Transcription is decoded by the ribosome to produce a specific amino acid chain (or polypeptide) that will later fold into an active protein  In bacteria: occurs in cytoplasm, where large and small subunits of the ribosome are located, and bind to the mRNA  In Eukaryotes: occurs across membrane of ER in a process called vectorial synthesis; ribosome facilitates decoding by inducing the binding of tRNAs with complementary anticodon sequences to that of the mRNA; tRNAs carry specific amino acids that are chained together into a polypeptide as the mRNA passes through and is read by the ribosome TFIID TFIIA TFIIB TFIIF TFIIE  No spaces between codons; codons are adjacent  Genetic code is non-overlapping; each nucleotide is part of one codon  Genetic code degenerate; most amino acids with similar properties are specified by related codons  Genetic code is (nearly) universal with minor exceptions, each triplet/codon has the same meaning in all organisms Mitosis  Interphase – G1 (growth, cellular metabolism); S (DNA replication, chromosome duplication); G2 phase (preparation for mitosis); M (chromosomal “pas de deux” and cytokinesis)  Prophase – initiation of spindle formation; condensation of duplicated chromosomes; fragmentation of ER and Golgi; nucleolus disappears; nuclear membrane breaks down; spindle microtubules invade the nuclear space;  Prometaphase – chromosome move toward he equator of the spindle  Metaphase – duplicated chromosomes migrate to the equatorial plane (metaphase plate) of the cell and the nuclear membrane breaks down; duplicated chromosomes condense under the influence of condensing;  Anaphase – sister chromatids of each duplicated chromosome move to opposite poles of the cell; centromeres split and chromatids separate; chromosomes move toward opposite spindle poles; spindle poles move further apart;  Telophase – Chromosomes de-condense and new nuclear membranes form; chromosomes cluster at opposite spindle poles; chromosomes become dispersed ad de-condense; nuclear envelope assembles around chromosomes; Golgi and ER reform; daughter cells form by cytokinesis;  Interphase – membrane forms between daughter cells (cytokinesis)   Before – 46 chromosome; During – 92; After – 46; Meiosis  n number of chromosomes – the haploid (single set of unpaired chromosomes) state  2n chromosomes – the diploid state  DNA replication and TWO cell divisions  Chiasmata – cross over junctions in chromosomes Meiosis I  Prophase Lepronema – chromosomes condense Zygonema – homologous chromosomes begin to pair Pachynema – homologous chromosomes fully paired Diplonema – homologous chromosomes separate, except at chiasmata Diakinesis – paired chrom. condense further and attach to spindle fibres  Metaphase I – paired chrom. align on equatorial plane  Anaphase I – homo. chrom. disjoin and move to opposite poles of the cell  Telophase I – chrom. movement is completed; new nuclei forms  Produces two haploid daughter cell that are genetically distinct Meiosis II  Resembles a mitotic division but products are haploid; produces four non-identical haploid (n) cells
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