CSB349 Lecture 4.doc

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Cell and Systems Biology
Alan Moses

CSB349 Lecture 4 – Moses Major classes of genomic DNA: Euchromatin Heterochromatin Nucleolus: Ribosomal transcription The genome is not frozen in place. It is dynamic! Chromosome territory: each chromosome takes a territory in the nucleus. To experiment this, (similar to FISH) all the chromosomes are labelled different colour and all fluoresced together to show the positions of the chromosome occupying their own place  show NON RANDOM ORGANIZATION One hypothesis suggests that chromosome territories allow for functional compartmentalization. Different chromosomes/DNA is placed together to perform certain function or maintain some gene expression (patterns). For example: the nucleolus. The positions of chromosomes are probabilistic, which means that copies of the chromosomes can be found at diff positions in diff cells Experiment: To show that chromosome territories are largely preserved. The genome in a cell was stained with two different colours: red and green. The combination turned the nucleus yellow. Photo bleaching was performed: part of the nucleus was zapped with a laser long enough to destroy the green fluorescent protein. The resulting nucleus was part yellow and part red. The cell then underwent mitosis and it was seen that the duplicates of the chromosomes held the same relative positions in the nucleus as the originals. Technique to study genome organization: which region is near which region in the genome? Chromosome conformation capture (3C) The DNA is cross-linked which means that the regions close to each other are glued together. The DNA is then digested by restriction enzymes to create fragmentt of DNA that are cross-linked to one another. The fragments are then ligated and reverse cross-linked with the ligation sites present in the middle of the
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