Biochemistry

Figure 9.2 - M-RNA biosynthesis Ribosome consist of two The M-RNA synthesis process begins with the fact that a DNA molecule with a double helix is unwound, and an M-RNA molecule is built on each of its strands according to the principle of complementarity (Fig. 9.2). Opposite each nitrogenous base of DNA, the corresponding nitrogenous base of M-RNA is built (Fig. 9.3). As a result, the matrix RNA molecule accurately repeats the sequence of nitrogenous bases of DNA, and therefore the genetic information. The portion of the DNA molecule responsible for the synthesis of a particular M-RNA is called an operon. It consists of a regulatory gene responsible for controlling the synthesis of M-RNA; gene operator, "supervising" the beginning of the synthesis, and a group of structural genes that provide the synthesis of M-RNA. M-RNA with received information is separated from DNA and connected with ribosome, which is consisting from ribosomal RNA (R-RNA), synthesized also on special DNA genes. subparticles, they are capable of reversibly dissociating at a reduced concentration ofMg 2+ . The large and small subunits of the ribosomes contain one RNA molecule with a molecular weight of 1.7 * 10 6 and 0.7 x 10 6 , respectively, and several tens of protein molecules. M-RNAs are converted into polyribosomes or polysomes when combined with ribosomes, on which the synthesis of polypeptide chains that form the primary structure of the protein takes place. The process of protein synthesis is preceded by the activation of amino acids during interaction with ATP, while aminoacyladenylates are formed and pyrophosphate is released. From aminoacyladenylate, the remainder of the amino acid is transferred to T-RNA specific for each amino acid and enters into the ribosomes as aminoacyl-T-RNA. The formation of aminoacyladenylate and the transfer of the amino acid residue to T-RNA are catalyzed by the same enzyme, aminoacyladenylate synthetase, which is strictly specific for each amino acid and each T-RNA. T-RNA have a cruciform configuration resembling a clover 183