DNA supercoiling. DNA is a big molecule Ruptured viral particle (bacteriophage) X95 000 DNA about 1.7µm © 2010 Paul Billiet ODWSODWS.

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Presentation transcript:

DNA supercoiling

DNA is a big molecule Ruptured viral particle (bacteriophage) X DNA about 1.7µm © 2010 Paul Billiet ODWSODWS

Some DNA molecules OrganismMolecular mass / 10 6 Daltons Base pairs x 10 6 Length Virus ФX µm E. coli mm Human m (46 molecules) © 2010 Paul Billiet ODWSODWS

THE NUCLEOSOME Uncoiled the DNA of a human would stretch 2m The average diameter of a nucleus is 10µm The problem: To pack the DNA into the nucleus and yet have access to the genetic information. © 2010 Paul Billiet ODWSODWS

THE NUCLEOSOME Histones are made of a lot of basic amino acids Combined with acidic DNA they make a stable nucleoprotein called chromatin Histone core = an octomer (8 histone molecules) Histone molecules © 2010 Paul Billiet ODWSODWS

DNA wraps twice round the core DNA strand © 2010 Paul Billiet ODWSODWS

DNA held in place by another histone (H1) = the nucleosome H1 © 2010 Paul Billiet ODWSODWS

Nucleosomes are joined by linker DNA Linker DNA © 2010 Paul Billiet ODWSODWS

DNA super coiling DNA double helix Nucleosome beads on a string 30-nm chromatin fibre © 2010 Paul Billiet ODWSODWS

DNA super coiling 30-nm chromatin fibre Chromosome in extended form Condensed section of chromosome in mitosis © 2010 Paul Billiet ODWSODWS

DNA super coiling Condensed section of chromosome in mitosis Condensed chromosome © 2010 Paul Billiet ODWSODWS

Nucleosome functions Nucleosomes help to supercoil the DNA molecule Nucleosomes help to regulate gene expression (transcription) © 2010 Paul Billiet ODWSODWS

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