Biochemistry

All these data allowed American chemists .T.Watson and F.Crick to create a model of the secondary structure of DNA, which is a double-stranded antiparallel helix. Schematically, this can be shown in the form of a spiral staircase (Fig. 5.3). In addition to the primary and secondary structures, the tertiary structure of nucleic acids associated with the spatial arrangement of DNA is also distinguished. Ribonucleic acid. The structure of RNA by the nature of the bonds between individual nucleotides of the chain is the same as in the DNA molecule. The pentose residue of one nucleotide in the RNA is coupled with an ester bond to the phosphoric acid residue of another mononucleotide. Most types of RNA, unlike DNA, are a single - stranded helix. The RNA strand spins by itself into a spiral, forming hydrogen bonds between the nitrogenous bases adenine-uracil-guanine-cytosine. RNA is concentrated mainly in the cytoplasm, but is often found in the nucleus. The nucleolus and ribosomal fraction of microsomes are especially rich in RNA. RNA performs other functions than DNA. It “ reads ” information from DNA about the alternation of nitrogenous bases and carries it into the cytoplasm. RNA is responsible for the specificity of the synthesized molecules. There are three main types of RNA in cells: matrix - informational (M-RNA), ribosomal (R-RNA) and transport (T-RNA). Figure 5.3 - Schematic representation of the DNA double helix 120