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U of M GCD 3022 - Structure of Bacterial Chromosomes
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GCD 3022 1st Edition Lecture 15Outline of Last Lecture I. Nucleotide Structurea. Three componentsi. Phosphate groupii. Pentose sugariii. Nitrogenous Baseb. Differences between DNA and RNAi. Sugar ii. BasesII. Bonds in DNA/RNAa. Phosphodiester linkagesb. Hydrogen bondsIII. Nitrogenous basesa. Purinesb. Pyrimadinesc. Chargraff’s ruleIV. DNA structurea. Double helixb. AntiparallelThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.c. ComplementaryV. RNA structurea. Double stranded regionsb. Change in base pairingsOutline of Current LectureI. Structure of bacterial chromosomesa. Locationb. Overall shape/structurei. Loop domainsii. DNA supercoilingII. Organization of Eukaryotic chromosomesa. Chromosome replication and segregationi. Three types of DNA sequencesb. Compaction of DNAi. Process: interphase and metaphaseii. Heterochromatiniii. EuchromatinIII. Nucleosomesa. Definitionb. Componentsi. Histone proteinsii. DNACurrent LectureI. Structure of bacterial chromosomesa. Location: bacterial chromosomal DNA is not located in a nucleus (only found in eukaryotic cells), but instead it is inside a nucleoid. The nucleoid is not bound by a membrane so the DNA is in direct contact with the cytoplasm. b. Overall shape/structure: in order to fit inside the nucleoid, bacterial chromosomal DNA must be compacted about 1000 foldi. Loop domains: creation of loops from a large circular chromosome, first step of compaction in bacterial DNA. Number of loops varies according to size of the bacterial chromosome and the species. ii. DNA negative supercoiling: secondary compaction method that helps in the compaction of the chromosome and creates tension that may be released by DNA strand separation (providing easier access for DNA binding proteins)II. Organization of Eukaryotic chromosomesa. Chromosome replication and segregationi. Three types of DNA sequences1. Origins of replication: chromosomal sites necessary to initiate DNAreplication, occur about every 100,000 base pairs2. Centromeres: involved in the segregation of chromosomes3. Telomeres: specialized regions at the end of chromosomes that are important for replication and stabilityii. Chromatin: DNA-protein complex that is necessary for compaction of linear DNA in eukaryotic cellsb. Compaction of DNAi. Heterochromatin: tightly compacted regions of chromosomes that are transcriptionally inactive. Two types:1. Constitutive heterochromatin: regions that are always heterochromatic; permanently inactive (in regards to transcription); usually contain highly repetitive sequences2. Facultative heterochromatin: regions that can interconvert between euchromatin and heterochromatinii. Euchromatin: less condensed regions of chromosomes that are transcriptionally active. Form 30 nm fibers of radial loops domains.iii. Process: interphase and metaphase1. Interphase: chromosomes are not uniformly condensed (euchromatin and heterochromatin regions)2. Metaphase: level of compaction increases so chromosomes can align and properly sort to daughter cells. Sister chromatids have an overall diameter of 1,400 nm (also much shorter than in interphase). Highly condensed metaphase chromosomes undergo very little gene transcription.III. Nucleosomesa. Definition: repeating structural unit of eukaryotic chromatin. Overall structure resembles “beads on a string”b. Componentsi. Histone proteins: octamer of proteins that DNA is wrapped around. 1. Contain positively charged amino acids (lysine and arginine) whichbind to the phosphates along the DNA backbone2. Have a globular domain and have a flexible charged “tail”ii. DNA: appears as a ribbon that wraps around histone


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U of M GCD 3022 - Structure of Bacterial Chromosomes

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