Lecture 2 - 011209

Lecture 2 - 011209 - Chromatin Lecture 2 MBOC old = 207-233...

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Chromatin Lecture 2 MBOC old = 207-233 MBOC new = 210-245
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Concepts • Know the four Core Histones • Understand the structure of the Nucleosome • Understand the relationship between Histones and DNA • What is the Chromatin Fiber? • What is Epigenetic Inheritance? • What is heterochromatin?
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Packaging DNA • All Eukaryotes package DNA • 48 million nucletides long = 1.5 cm • In mitosis Ch22 measures 2um – Corresponds to an end to end compaction of 10,000 fold
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Compaction and Chromatin • Compaction of DNA is achieved by proteins that coil and fold DNA • Proteins that fold DNA are: – Histones – Non histones • Protein + DNA is called Chromatin
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The chromatin fiber in Interphase as seen using an electron microscope
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Nucleosomes • Basic unit of chromosome structure • The presence of nucleosomes in a bead on a string confirmation compresses DNA into a chromatin thread about 1/3 its length. • Each nucleosome core particle consists of 8 histone proteins (Histone Octomer) and ~147 nucleotides of double stranded DNA
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Structural organization of nucleosomes
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Identification of individual subunits in the nucleosome
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X-Ray Diffraction of to identify 3-D structure of nucleosome Flat-disc like with tight interactions between proteins and DNA
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The four core histones - Small proteins - N-terminal tails are covalently modified - characteristic histone fold - Form dimers
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Core histones are highly conserved • Most highly conserved proteins across species – For example amino acid sequence of histone H4 in peas and cows differs by just two amino acids – High conservation suggests important functional role in all eukaryotes • Mutations in histone sequence are usually lethal • Non-lethal changes affect gene expression
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Histone proteins must Interact to form the nucleosome • Histone H3 binds to H4 • Histone H2A binds to H2B • The two Histone H3-H4 dimers bind to each other to form tetramers • Two H2A H2B dimers interact with the tetramere to generate the histone octamer • DNA winds around the histone octamer 1.7 times
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Histone Octamer - Note all 8 histone N-
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This note was uploaded on 03/30/2009 for the course MCDB 144 taught by Professor Dr.clarkanddr.lowry during the Spring '09 term at UCLA.

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Lecture 2 - 011209 - Chromatin Lecture 2 MBOC old = 207-233...

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