GCD 3022 1st Edition Lecture 15 Outline of Last Lecture I Nucleotide Structure a Three components i Phosphate group ii Pentose sugar iii Nitrogenous Base b Differences between DNA and RNA i Sugar ii Bases II Bonds in DNA RNA a Phosphodiester linkages b Hydrogen bonds III Nitrogenous bases a Purines b Pyrimadines c Chargraff s rule IV DNA structure a Double helix b Antiparallel These 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 Complementary V RNA structure a Double stranded regions b Change in base pairings Outline of Current Lecture I Structure of bacterial chromosomes a Location b Overall shape structure i Loop domains ii DNA supercoiling II Organization of Eukaryotic chromosomes a Chromosome replication and segregation i Three types of DNA sequences b Compaction of DNA i Process interphase and metaphase ii Heterochromatin iii Euchromatin III Nucleosomes a Definition b Components i Histone proteins ii DNA Current Lecture I Structure of bacterial chromosomes a 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 fold i 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 chromosomes a Chromosome replication and segregation i Three types of DNA sequences 1 Origins of replication chromosomal sites necessary to initiate DNA replication occur about every 100 000 base pairs 2 Centromeres involved in the segregation of chromosomes 3 Telomeres specialized regions at the end of chromosomes that are important for replication and stability ii Chromatin DNA protein complex that is necessary for compaction of linear DNA in eukaryotic cells b Compaction of DNA i 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 sequences 2 Facultative heterochromatin regions that can interconvert between euchromatin and heterochromatin ii Euchromatin less condensed regions of chromosomes that are transcriptionally active Form 30 nm fibers of radial loops domains iii Process interphase and metaphase 1 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 Nucleosomes a Definition repeating structural unit of eukaryotic chromatin Overall structure resembles beads on a string b Components i Histone proteins octamer of proteins that DNA is wrapped around 1 Contain positively charged amino acids lysine and arginine which bind to the phosphates along the DNA backbone 2 Have a globular domain and have a flexible charged tail ii DNA appears as a ribbon that wraps around histone proteins
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