Lecture 4 Part 2

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25 Mar 2012
Lecture 5 Jan. 23/12
Genomes and Chromosomes (P2)
Chromosomal packaging
Chromosomes chromatin nucleosomes
Nucleosomes circular histone protein + strings of wrapped DNA
Histones rich in lysine and arginine, +ve charge attracts –ve DNA
Special H1 histone organizes nucleosomes into tighter configuration
H1 histones changes the shape of the chromatin strand into a spiral
Chromatin packing
DNA wraps around histones
H1 histones contorts shape
Condensons (proteins) grab onto loops and condense chromatin further
Final product of highly condensed chromatin
Needed around centromeres to keep structural stability
Used in to suppress gene expressions
Condensed DNA is difficult to unravel for gene expression
Ex. Found in an X chromosome in females to control gene dosages, X inactivation
High lysine residues on histones (becomes methylated)
Large +ve attraction to DNA –ve charge
Non-condensed chromatin
Used when gene expression is needed
Ex. Interphase, transcription
Higher acetylate groups, reduces charges of lysines
Smaller +ve attraction to DNA, DNA can spread out more
Orientation of gene expression
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