Lecture 28 SRR F-2011 - Biology 313 Lecture 28 Nov 2 2011...

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Biology 313, Lecture 28 Nov 2, 2011 What is the molecular structure of this?
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Chapter 11 : Chromosome Structure Problems (through Section 11.3 ) Concept Checks (1-7) Worked Problems: 1 Comprehension and Application Questions at end of Chapter: 1-11; 24-27; 29; 31-32
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Chapter 11 : Chromosome Structure and Transposable Elements 1. Tertiary DNA structure: chromosome packing C. Eukaryotic chromosome packing: nucleosomes D. Chromosome decondensation: puffs and histones 2. Centromeres and telomeres
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Centromere Structure -- There is no “consensus sequence” for a centromere (a consensus sequence is a DNA sequence that is conserved among organisms because it confers a special function) -- Instead, CenH3 histone is present. Cen3 causes the chromatin to condense into a “centromere”.
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Centromere Structure How does Cen3 know where to go on the chromatin? How does it remodel the chromatin to make a centromere? A VERY HOT RESEARCH TOPIC TODAY!!! This is an epigenetic change : a stable alteration of chromatin structure that is heritable
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Telomere Structure -- Telomeres are the ends of chromosomes -- Nobel Prize (2009) to Jack Szostak, Elizabeth Blackburn, Carol Greider (UCSF, Harvard): telomere structure and how they replicate (Ch 12) -- Chromosome breaks produce ends that are unstable, and tend to stick to one another and/or be degraded; telomeres bind proteins that act as a “cap” to prevent this; telomere proteins stabilize chromosome ends
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Telomere Structure -- Telomere consensus sequences: short repeats of [A/T] followed by several G : 5’- (A or T) m G n -3’ (m is usually 1-4, and n is >1) -- This repeat is repeated thousands of times -- G-rich strand protrudes, called the 3’ overhang G-rich strand
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In mammalian cells the G-rich strand folds over and pairs with a short stretch of complementary sequence to form a t-loop The t-loop prevents the ends from being degraded Telomere Structure
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