1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
|
<html>
<head>
<title>The Nucleosome</title>
<link rel="stylesheet" href="../css/style.css">
</head>
<body>
<div class="navigation" id="breadcrumb">
<a href="index.html?action=clearAll&module=common_functions">Main page</a> > The Nucleosome
</div>
<div id="text-content">
<h1>The Nucleosome</h1>
<div class="greeter">
<p>
Some things in nature are astonishing: a human (A) is 1.75m/5.74ft on average, one of his hairs (B) has a diameter of only 0.1mm/0.004in, that is approx. 20.000 times smaller. Display (C) shows you two cells (green), their DNA in the nucleus is stained blue. Cells vary in shape and sizes, typically they have a diameter of about 20μm. Their nucleus (D) is again smaller, only measuring 5μm from end to end - that is 350.000 times smaller than the 1.75m/5.74ft human. And the DNA in the nucleus needs to be even smaller - right? To some extent yes, because DNA is a very thin fiber but also a particularly long one, that is to say 2m/6.56ft! How to fit 2m/6.56ft of DNA into the nucleus, which is 350.000 times smaller than the average human?
</p>
<div class="img">
<img id="collage" src="../images/collage.png" alt="Several magnitudes of sizes" width=70% align=bottomright>
<div>(Source of images: Wikipedia)</div>
</div>
<p>
The answer is indeed simple: it is all about packaging the DNA in a clever way! Imagine a wool fiber that is very thin as well as very long, but if it is wrapped around a mandrel, it can be efficiently stashed. Of course, there are no mandrels in nature to wind up the DNA, their role is carried out by proteins.
<h3> DNA + proteins = nucleosome </h3>
To organize the DNA in the nucleus properly, the DNA is wrapped around specialized proteins. These proteins are called histones, they form a core around which the DNA is wrapped like the wool fiber around the mandrel. In the following example, you can take a look at the complete structure.
</p>
<div class="actions">
<p>
Can you identify the double-stranded DNA and the histone core?
</p>
<!--<a href="nucleo1_en.html?action=loadProject&module=common_functions&filename=projects/NCP_start.bvp">Structure of a nucleosome</a>-->
</div>
<div class="navigation">
<p>
You can learn more about the composition of the nucleosome on the next page.
</p><br>
<a href="nucleo2_en.html">next</a><br>
<a href="index.html?action=clearAll&module=common_functions">Main page</a>
</div>
</div> <!-- end of greeter ??? -->
</div> <!-- end of text-content -->
</body>
</html>
|
