BIO130H1 Lecture Notes - Lecture 5: Hybridization Probe, Rubber Band, Nucleoid

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21 Jan 2019

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BIO130 Lecture 5 21/01/19
The Human Genome:
It’s divided into 50% unique sequences and 50% repeated sequences
Only 1.5% of the genome encodes proteins
INTRONS protein-coding regions
o Part of the unique sequences
TRANSPONS left over DNA from viruses that were inserted in the human
genome over evolutionary time
o Thought to provide structural support to chromosomes
o Help them fold properly
It is unknown what the role of the repeated sequences is but it’s unlikely that it
has no role at all
Non-repetitive DNA sequences are yet to be fully understood as in what their
purpose is
Packaging of DNA in the cell:
In a non-packaged state, even the small prokaryotic genome would occupy a
lot of the cell volume
o This is even more of a problem in eukaryotic cells
In prokaryotes, the DNA is condensed through folding it 1000 times
o Forms the prokaryotic nucleoid
o Prokaryotes don’t have chromatin
Important components for packaging:
o Positively charged polyamines
They are positively charged in order to neutralize the negative
charge of the backbone
Numerous nucleoid-associated proteins (NAPs)
E.g. H-NS (histone-like nucleostructuring protein), HU,
Supercoiling of DNA by the enzyme topoisomerase
Supercoiling twisting a molecule in order to shorten it
Think of twisting a rubber band
Karyotype artificial array of paired chromosomes in numerical order
Diagnostic aid
Fluorescence in situ hybridization (FISH):
Very common technique
You create a probe
Label it with color (e.g. blue)
Mix it together on a slide
Denature the DNA by heating it melt the probe into two single strands
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