Chapter 19 - Eukaryotic Genomes

Chapter 19 - Eukaryotic Genomes - Chapter 19 Class Notes...

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Chapter 19 Class Notes – Eukaryotic Genomes – Page 1 Max Sauberman AP Biology – Mr. Schilp Chapter 19 Eukaryotic Genomes: Organization, Regulation, and Evolution Eukaryotic Genomes: Two features of eukaryotic genomes are a major information-processing challenge. The typical eukaryotic genome is much larger than that of a prokaryotic cell. Cell specialization limits the expression of many genes to specific cells. The DNA-protein complex chromatin is ordered into higher structural levels than the DNA-protein complex in prokaryotes. Chromatin structure: Eukaryotic DNA is precisely combined with a large amount of protein, called histone protein. Eukaryotic chromosomes contain an enormous amount of DNA relative to their condensed length. Nucleosomes: Proteins called histones are responsible for the first level of DNA packing in chromatin. The association of DNA and histones seems to remain intact throughout the cell cycle. In electron micrographs, unfolded chromatin (DNA and histone) has the appearance of beads on a string. Each bead is a nucleosome, the basic unit of DNA packaging. Higher Levels of DNA Packing: The next level of packaging forms the 30-nm chromatin fiber: The 30-nm fiber forms looped domains, a 300-nm fiber. Below the looped domains is a scaffold of nonhistone proteins. In a mitotic chromosome, the looped domains coil and fold (during the condensation of chromosome during prophase), forming the metaphase chromosome. The loops are packed even closer. At 300-nm, it is maximally compacted and becomes solidified. Interphase Chromatin: Interphase chromatin is usually much less condensed than that of mitotic chromosomes. Much of the interphase chromatin is present as a 10-nm fiber, and some is 30-nm fiber, which in some regions is folded into looped domains.
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Chapter 19 Class Notes – Eukaryotic Genomes – Page 2 Interphase chromosomes have highly condensed areas, called heterochromatin, and less compacted areas called euchromatin. Gene Expression: All organisms must regulate which genes are expressed at any given time. A multicellular organism’s cells undergo cell differentiation, specialization in form and function. Differential Gene Expression: Differences between cell types result from differential gene expression, the expression of certain genes by cells within the same genome. In each type of differentiated cell, a unique subset of genes is expressed. Many key stages of gene expression can be regulated in eukaryotic genes. Histone Modifications: Chemical modification of histone tails can affect the configuration of chromatin and thus, gene expression. In histone acetylation, acetyl groups are attached to lysines in histone tails, loosening chromatin structure (chromatin becomes less compact), thereby enhancing transcription. DNA Methylation:
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This note was uploaded on 03/17/2011 for the course BIO 101 taught by Professor Sullivan during the Spring '08 term at Harvard.

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Chapter 19 - Eukaryotic Genomes - Chapter 19 Class Notes...

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