Chromosomal Structure

<p><b>Bacterial Chromosome Structure</b><br />

<b>Prokaryotic cells</b> (bacteria) contain their chromosome as circular &nbsp;DNA. &nbsp;Usually the entire genome is a single circle, but often there are extra circles called plasmids. The DNA is packaged by DNA-binding proteins.</p>

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<b>Eukaryotic Chromosome Structure</b>

<b>Eukaryotic cells</b> contain their DNA within the nuclear membrane. Our bodies manage both the storage problem and the gene expression problem through many levels of DNA compression. Compressing the genome allows it to fit inside the nucleus of a single cell. By controlling which parts of the genome are more or less tightly compressed, a cell can access just those parts of the DNA which are necessary to its long-term role in the body, while retaining the flexibility to respond to pressing demands from a changing environment.</p>

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The DNA double helix is bound to proteins called histones. &nbsp;The histones have &nbsp;positively charged (basic) amino acids to bind the negatively charged (acidic) DNA. &nbsp;Here is an SDS gel of histone proteins, separated by size (those migrating down farthest are smaller). &nbsp;</p>

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<img src="/28f32956-2c50-5e9c-bdd5-e2d50e279c5f.png"/></p>

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<img src="/a637359f-fbb0-568a-8f16-2e425d29f80a.png"/> &nbsp;&nbsp;

Methylation of histone or of&nbsp;DNA usually turns a gene off.

Acetylation of histone usually turns a gene on.

Phosphorylation -- we're not sure what that does. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>

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<img src="/17c93fab-2b47-5e80-9100-6cff2eeddc64.png"/> &nbsp;&nbsp;<img src="/2cb1d262-f87b-5a21-a350-64fcddf92504.png"/> &nbsp;&nbsp;&nbsp;&nbsp;DNA and histone proteins are packaged into structures called chromosomes.</p>

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Sequence of Genome Structures is &nbsp;--Nucleosome i.e. DNA wrapped around protein core and with 8 histones (protein) makes a histone core.&nbsp;DNA can then wrap around these and form nucleosome.&nbsp;

Linkers then connect nucleosomes to form a Chromatosome. &nbsp;&nbsp;</p>

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<img src="/0999c426-fc9e-505d-ac37-f500ae22662b.png"/> &nbsp;<img src="/d08a3c27-8cfc-5465-8183-998948656a12.png"/> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<img src="/6ef5d16d-8c8e-5a23-aa6f-088ea512bc83.png"/> &nbsp;&nbsp;</p>

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Each Chromatosome holds 166bp of DNA so they have to coil &nbsp;into a Chromatin fibre --finally chromatin fibres fold on themselves to produce individual chromosomes--linear (humans anyway)</p>

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<img src="/6fdfc29c-24d2-5fc5-80ab-1a788c3441d4.png"/> &nbsp; &nbsp;&nbsp;&nbsp;&nbsp;<img src="/d68a9a06-937f-5238-8ca9-12fc365e268b.png"/>

&nbsp;Chromatin folds to form a condensed, linear structure called a chromosome. A complete set of 46 chromosomes fits inside the nucleus of each cell in the human body.</p>

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