Biology Chapter 19

Biology Chapter 19 - Chapter 19: Eukaryotic Genomes...

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Chapter 19: Eukaryotic Genomes Organization, Regulation, and Evolution How Eukaryotic Genomes Work and Evolve - In all organisms, DNA associates with proteins that condense it - Chromatin: DNA protein complex is ordered into higher structural levels than the DNA protein complex in prokaryotes Chromatin Structure is Based pm Successive Levels of DNA Packing - Eukaryotic DNA is precisely combined with a large amount of protein o Resulting chromatin undergoes striking changes in the course of the cell cycle - As a cell prepares for mitosis, its chromatin coils and folds up (condenses), forming a characteristic number of short, thick chromosomes Nucleosomes, or “Beads on a String” - Histones: Proteins responsible for the first level of DNA packing in chromatin o Have a high proportion of positively charged amino acids, and they bind tightly to the negatively charged DNA - Mass of histone in a chromatin is equal to the mass of DNA - Nucleosome “bead”: the basic unit of DNA packiung: the “string” between the beads is called linker DNA o Consists of DNA wound around a protein core composed of two molecules each of four types of histone: H2A, H2B, H3 and H4 o Molecule of the fifth histone is called H1 - Association of DNA and histones in nucleosomes seems to remain essentially intact throughout the cell cycle - Histones leave the DNA only transiently during DNA replication Gene Expression Can be regulated at Any Stage, But the Key Step is Transcription - Cell Differentiation: Development of a multicellular organism, resulting in several or many differentiated cell types Differential Gene Expression - Differential Gene Expression: The expression of different genes by cell with the same genome - Genomes of eukaryotes may contain tens of thousands of genes - The nuclear envelop separating transcription from translation in eukaryotic cells offers an opportunity for post transcriptional control in the form of RNA processing that is absent in prokaryotes - Eukaryotes have a greater variety of control mechanisms operating before transcription and after translation - In prokaryotes, transcription is the most important control point - Gene expression is often equated with transcription for both prokaryotes and eukaryotes o The greater complexity of eukaryotic cell structure and function provides opportunities for regulating
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This note was uploaded on 11/04/2010 for the course BIO 107 taught by Professor Abott during the Fall '09 term at UConn.

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Biology Chapter 19 - Chapter 19: Eukaryotic Genomes...

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