How is a ribosome made and what is its structure?

Biology
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* P sites and A sites and subunits

Dec 1st, 2014

The ribosome is the molecular machine inside the cell that makes proteins from amino acids in the process called translation . It binds to a messenger ribonucleic acid (mRNA) and reads the information contained in the nucleotide sequence of the mRNA. Transfer RNAs (tRNAs) containing amino acids enter the ribosome in a special pocket, or binding site, called the acceptor site (A site). Once correctly bound, the ribosome can add the amino acid on the tRNA to the growing protein chain.

Structure

The ribosome is made up of two parts, called subunits. The larger of the two subunits is where the amino acids get added to the growing protein chain. The small subunit is where the mRNA binds and is decoded. Each of the subunits is made up of both protein and ribonucleic acid (RNA) components.

The small ribosomal subunit is made up of one ribosomal RNA (rRNA) and approximately twenty-one proteins in prokaryotes (bacteria) and approximately thirty-three proteins in eukaryotes (mammals). In prokaryotes, the large ribosomal subunit contains two rRNAs—one large one and one small one—and approximately thirty-one proteins. In eukaryotes, the large subunit is composed of three rRNAs—one large one and two different small ones—and approximately forty-nine proteins. In eukaryotic cells, ribosomal subunits are synthesized in the nucleolus and then exported to the cytoplasm before use.

The rRNAs have many regions of self-complementarity, that is, regions within the rRNA that can form base pairs with other regions of the same rRNA, linking them together. This self-complementarity produces highly

[img src="http://www.biologyreference.com/images/biol_04_img0400.jpg" height="279" alt="A color-coded cryo-EM map of an E. coli ribosome showing the interface between the small (30S) and large (50S) ribosomal subunits." width="348">
A color-coded cryo-EM map of an E. coli ribosome showing the interface between the small (30S) and large (50S) ribosomal subunits.

structured RNA molecules that serve as the core of the ribosome. In fact, rRNAs make up most of the mass of the ribosome. The proteins bind to various parts of the rRNAs to fill in the ribosome's structure.

Researchers have worked for many years to try to determine what the ribosome's structure is at the atomic level. How are all the atoms that make up the ribosome arranged in three-dimensional space? On a gross level, the ribosome looks something like an oyster with one of its shells somewhat smaller than the other. The two subunits are joined to each other by interactions between the rRNAs in one subunit and proteins in the other subunit. There may also be interactions between an RNA on one subunit and an RNA on the other subunit and between proteins on the two subunits.


Read more: http://www.biologyreference.com/Re-Se/Ribosome.html#ixzz3Kbuzisc4

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