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Lecture 19

Biochemistry 3380G Lecture Notes - Lecture 19: Nuclear Matrix, Nucleosome, Histone H4

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Topic 19 – Chromatin
Human DNA must be condensed
The human genome is about 3 x 109 base pairs long
At 0.34 nm per base pair in the double helix, that’s 102 cm
Two copies of each chromosome per cell
Human DNA must be condensed about 10 000 – fold to fit inside the nucleus
DNA packaging is highly organized
Despite being condensed, DNA must remain available for replication, repair and gene
Eukaryotic DNA is condensed with the help of specialized proteins
The protein/DNA complex is called chromatin
QUESTION: We have a DNA helix, what is the best way to package the DNA?
ANSWER: Like a thread
The proteins we use are called histones
They are eukaryotic proteins involved in condensing DNA
Contain fewer than 200 amino acids
Very rich in lysine and arginine residues
oMakes sense – they are the side chains that are positively charged, and the
phosphates on DNA are negatively charger
5 different types
oH1, H2A, H2B, H3 and H4
Human histone H1
Largest human histone
There are lots of lysine and arginine
Histones are rich in arginine and lysine
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