24_Lieb_euk_gene_reg2 - Biology 202-Lieb Chromatin and...

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Biology 202-Lieb Chromatin and Eukaryotic Gene Regulation II Page 1 of 2 I. Genomes, genes, and chromosomes (review from first half) The genome is all of the DNA in an organism. In eukaryotes, the genome is organized into chromosomes . Before replication, a chromosome has one chromatid ; after replication, there are two identical chromatids. At mitosis, chromatids segregate from one another into different daughter cells. Each chromatid consists of a single double-stranded DNA molecule, complexed with proteins. II. Chromatin Genomic DNA is associated with specialized proteins; DNA packaged into these proteins is called chromatin . The basic unit of chromatin is the nucleosome , which consists of DNA wrapped around an octamer of histone proteins. The eight polypeptides in the octamer are two each of histone H2A, histone H2B, histone H3, and histone H4. Nucleosomes are in organized into higher-order structures. Post-translational modification of histone proteins (methylation, acetylation or phosphorylation) play a critical role in regulating gene expression. Also, there are
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