Proteins

Proteins are synthesized from amino acids by living organisms on the basis of information encoded in genes. Each protein consists of a unique sequence of amino acids, which is determined by the nucleotide sequence of the gene encoding this protein. The genetic code is composed of three «words», called kodonami every kodon is responsible for adherence to a protein amino acids: for example, corresponds to a combination of AUG methionine. Because DNA consists of four types of nucleotides, the total number of possible kodonov equals 64, as well as in proteins is 20 amino acids, many amino acids are determined by more than one kodonom. Genes encoding proteins transkribiruyutsya first sequence of nucleotides in a matrix RNA (mRNA) protein-RNA polymerase.

In mRNA can be read by ribosomes in the amino acid sequence of proteins immediately after transcription, and in eukaryotes, it is transported from the cytoplasm to the nucleus where the ribosomes. The rate of protein synthesis is higher in prokaryotes and may be as high as 20 amino acids per second.

The process of protein synthesis from mRNA is called translation. During the initial phase of protein biosynthesis, initiation, usually known metioninovy kodon small ribosome subunit, which with the help of protein factors, initiation joined metioninovaya transport RNA (tRNK). After recognizing the start kodona to a small subunit joins a large subunit and the second stage begins broadcasting - elongation. Each movement ribosomes from 5 'to 3' end of mRNA is read one kodon through the formation of hydrogen bonds between the three nucleotides (kodonom) mRNA and complementary RNA transport him antikodonom, joined by the corresponding amino acid. Synthesis of peptide bond catalyzes ribosomal RNA, rRNA, forming peptidiltransferazny center of ribosomes. Ribosomal RNA (rRNA) catalyzes peptide bond formation between the last amino acid and growing peptide amino acid attached to tRNK, position the atoms of nitrogen and carbon in a situation favorable for a reaction. Enzymes aminoatsil-tRNK-SYNTHETASES adds amino acids to their tRNK. The third and last stage of translation termination occurs when the ribosome stop kodona, after which the protein termination factors hydrolysis last tRNK from protein, stopping its synthesis. Thus, the ribosome proteins are always synthesized from N-to C-end.