General Index


Nucleoprotein Structures

Nucleosomes

Nucleosomes are complex structures that constitute the basic unit of Chromatin, the form of DNA organization in Eukaryota. Nucleosomes are formed by a protein core containing an octamer of Histones, strongly basic proteins largely conserved through Evolution. The basic character is due to their high content of Lysine and Arginine, that at the cell pH present positive charge and interact with the negative charge of phosphates in DNA. The structure of nucleosome is as follows:

The components of nucleosomes are the following: 1. Two copies of H2a histone:

There is another histone, H1 histone, that it is not part of the nucleosome but interacts with the linker DNA, that connects two succesive nucleosomes.



50s ribosomal subunit

Since 2000 we know the molecular structure of the 50s ribosomal subunit of the Archaea Haloarcula marismortui at a resolution of 2.4 angstrom units obtained by X-ray crystallography. Till now is the biggest structure ever resolved by this technique. It has been possible to locate 2833 nucleotides from a total of 3045 and 27 of the 31 different proteins of the subunit. These are located at the surface of the two molecules of rRNA (23s and 5s) except at the functional zone of the particle, that catalyzes peptide bond formation in protein synthesis.

Its components are: in the first place, 23s rRNA:


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