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lecture10 - LECTURE 10 16 September 2009(P J Hollenbeck...

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-1- LECTURE 10 16 September 2009 (P. J. Hollenbeck) BIOL231 DNA and Chromatin Structure Read pp. 171-193; note pp. 174-76; DVD 5.1, 2 Probs: Q5-6, 5-11 in ECB <So far this semester we have addressed how the cell is organized, how its boundaries work, what macromolecules are important for its function – and we have seen that the heavy lifting in the cell is mainly done by proteins. We have considered protein structure and function, and enzyme kinetics. Now we want to consider how proteins are synthesized and localized in the cell. To do this we begin with the genetic information that encodes primary protein structure: the genome, comprised of DNA. Let’s consider it’s structure now, creeping up on it from general to specific...> I. Basic Organization of DNA [figs 5-2 to 5-7; DVD 5.1] <When the chemical basis of heredity was being elucidated, a number of now “classic” experiments were carried out. You will learn about these in detail in your genetics course, but it is worth thinking about three now – Griffith’s S. pneumoniae experiment; Avery’s “transforming principle” expt, and the Hersey-Chase expt. Study pp. 174-176 of your text for a good summary. These set the stage for the determination in the early 1950s of the double helix structure of DNA by Watson & Crick (and Wilkins and Franklin). It is hard to appreciate how completely biology was changed by that single finding. The structure immediately revealed, in broad terms, how the genome replicates faithfully – that is, how the DNA instructions are copied.> (A) Structure and heredity – spectacular example of structure-function relationships (1) Replication – As soon as this structure was determined, it became apparent that if the two strands are separated, and a new strand is formed along each of them by complimentary base pairing (A:T , G ! C), then the result will be two new helices each with identical structure – identical nucleotide sequences to the original. At a stroke, this solved the long-standing problem of how biological information is carried faithfully from generation to generation. (2) Transcription – We will get to this soon, but it is equally clear that an RNA copy of any part of the DNA can be made in a similar fashion, and exported to the cytoplasm for translation (while the DNA remains safe and sound in the nucleus).
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