Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 13

In most cells the nucleus is a centrally located structure that is separated from the cytoplasm by the nuclear membrane (nuclear envelope). The region inside the nuclear membrane is called the nucleoplasm and usually has a granular appearance with a denser inner region called the nucleolus. This granular appearance is due to the presence of condensed chromatin which consists of DNA molecules and histone proteins. The histones function as physical spools around which the DNA is wound and stored in a very compact form (Figure 1.2). This spooling of DNA is essential since each cell, which on average is only around 12 μm in diameter (12 1/000th mm), has to store around 3 metres (10 feet) of DNA.

Figure 1.2 Chromatin and the spooling and storage of DNA