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Biology 1202B exam review notes

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Biology 1202B
Brenda Murphy

Biology Notes MurphyDNA Structure and Organization Chapter 13Human Genome1952 HersheyChase DNA inherited material1953 Watson CrickFranklin DNA structure double helix1956 TijoLevan 46 chromosomes in nucleus1963 MarjitSylvan Nass mtDNAInitially thought that the human genome consisted of ProteinUsed X ray fraction to examine Rosalind Franklin o X ray fraction the patterns reveal positions of the atoms in the crystal ie helical structureMature red blood cells DO NOT have 46 chromosomes because they do not contain a nucleus Diagram of Xray diffraction analysis of DNA Rosalind FranklinNucleotides building blocks of nucleic acids DNARNA Nucleotide basesugarphosphate CONTAINSTriphosphateDeoxyribose Sugar Ribose SugarNitrogenous Baseso Guanine G o Adenine A o Thymine T Uracil U o Cytosine CDNARNA are made of dNTP deoxynucloside triphosphateo ie dATP dCTP dTTP dGTP dUTP Nucleotide Nucleosidephosphate sugarbasedeoxyadenosinedeoxyuridinedeoxyguanosinedeoxycytidinedenoxythymidine 1Differences between RNADNARNA is VERY UNSTABLE because of the OH on the C2 physical structureDNA is stable because it DOES NOT have an OH on the C2DNA is double stranded whereas RNA is single strandedSubunits of DNA4 nucleotides subunits ACTG linked into a polynucleotide chain5 end has a phosphate 3 end has a OH hydroxyl groupThe C5 position of the deoxyribose 5 carbon sugar holds the phosphate o This is the sugar phosphate backboneThe phosphate bridges 3 to 5 from 2 different sugars in the sugar backbone3 to 5 phosphodiester bondDNA Double helixDistance between each pair of bases ex distance between ATCG is 034nmEach full twist of the DNA double helix 34nmRefer to Figure 136 page 2785 to 3 is ANTIPARALLEL 1 stand is 5 to 3 and the other strand is 3 to 5Chargaffs Rule the amount of purinesdouble ring structures AG equal to the number of pyrimidines single ring structuresCTTwo polynucleotide chains twist around each other in a right handed way Difference between rightlefthanded helicesIf you move along a helix in the direction of your right hands thumb and the helix turns in the direction of your right hands fingers then its a righthanded helix Picture the helix vertical if the front strands move from the lower left to the upper right then it is a righthanded helix2WatsonCricks model for DNA ReplicationComplimentary base pairing in the DNA double helix A pairs with T and G pairs with CThe two chains unwindseparateEach old strand is a template for the addition of complementary baseso The old strand becomes one of the strands in the final productThe result is two DNA helices that are exact copies of the DNA molecules with one old strand and one new strandSEMI CONSERVATIVE DNA REPLICATION StepsThe template strand with two nucleotides of the new strand are assembledIncoming A nucleoside triphosphate with an A base forms a complimentary base pair with the next nucleotide of the template strand attaches to TA phosphodiester linkage forms linking the newly added nucleotide to the end of the primer lengthening the strand one by oneo Hydrolysis provides energy for DNA chain elongation reaction Eukaryotic DNA OrganizationChromatin is the building block of chromosomesChromosomal ProteinsoHistones oNonhistonesHistones class of small positively charged basic proteins that are complexed with DNA in the chromosomes of eukaryotes Histones link to DNA by an attraction between their positive charges and the negatively charged phosphate groups of DNA5 histone proteins exist in most eukaryote cells H1 H2A H2B H3 H4Amino acid sequences of these proteins are conserved suggesting that they perform the same function in all eukaryotic organismsHistones pack DNA at several levels of chromatin structureMost fundamental structure nucleosome two molecules of each H2A H2B H3 and H4 combine to form a bead like structure under electron microscope total of 8 molecules used o Makes a 8protein nucleosome core particle around which DNA winds for almost 2 turnsA short segment of DNA the linker extends between one nucleosome and the nexto H1 forms a bead on a string looking structure under the electron microscopeThe diameter of the beads the nucleosomes is what gives this structure its name 10nm chromatin fiber o Each nucleosome and linker includes about 200 base pairs of DNA Refer to Figure 1318 on page 290One H1 molecule binds both to the nucleosome at the point where the DNA enters and leaves the core particle and to the linker DNAH1 binding of neighbouring nucleosomes beads on a string solenoid 30nm chromatin fiber o Solenoid inactive DNA3
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