Lecture 19 Bio325 Fall 07

Lecture 19 Bio325 Fall 07 - 1 Eukaryotic chromosome...

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Unformatted text preview: 1 Eukaryotic chromosome structure: Chromosomal DNA in eukaryotic cells is packaged with proteins to condense its length and regulate access to genes; the protein- DNA complex is called chromatin Histones are the primary protein components of chromatin. Two of each of the core histones (H2A, H2B, H3, and H4) form an octamer of proteins which wraps DNA ~ 2 times around its globular shape. This basic protein-DNA structure is the nucleosome . Fig. 13.3 Nucleosome-bound DNA then packs into higher order chromatin structures Fig. 13.4, 13.5 the highest levels of chromatin packing only occur during mitosis or meiosis 2 telomeres : specialized protein-DNA structures at the ends of linear chromosomes DNA polymerase cannot replicate the very end of the lagging strand template at the end of a linear chromosome (the end replication problem) Because of this, chromosomes would become steadily shorter in every cell division Fig. 13.9 The end replication problem is solved by the enzyme telomerase , a protein-RNA complex that synthesizes new DNA onto the lagging strand template to counteract the shortening problem. The template for DNA synthesis is the RNA component of telomerase telomeres consist of thousands of bp of repetitive sequence (for instance TTAGGG in humans); the telomerase RNA is complementary to this sequence the very end of a telomere is also bound by many telomere-specic proteins that protect it from degradation and prevent it from being recognized by the cell as DNA damage Fig. 13.10 3 near the center of each chromosome is the specialized structure called the centromere ; it also consists of thousands of bp of repetitive sequence (but different sequence from telomeres) the chromatin at the centromere is highly condensed and therefore looks thinner than the rest of the chromosome Movement of chromosomes during prometaphase occurs through formation of kinetochores , protein-based structures that form on each centromere. Some of the microtubules in the mitotic spindle attach to the kinetochores,...
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This note was uploaded on 06/19/2008 for the course BIO 325 taught by Professor Saxena during the Fall '08 term at University of Texas at Austin.

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Lecture 19 Bio325 Fall 07 - 1 Eukaryotic chromosome...

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