Nucleic acid metabolism involves the assembly and disassembly of the nucleic acids DNA and RNA. Both molecules have the task of storing genetic information. Disturbances in the synthesis of DNA can lead to mutations and thus to changes in genetic information.
What is nucleic acid metabolism?
Nucleic acid metabolism involves the assembly and disassembly of the nucleic acids DNA and RNA. Nucleic acid metabolism provides for the formation and degradation of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). In the process, DNA stores all genetic information long-term in the cell nucleus. RNA, in turn, is responsible for protein synthesis and thus transfers the genetic information to the proteins. Both DNA and RNA consist of nucleic bases, a sugar molecule and a phosphate molecule. The sugar molecule is linked to the phosphate residue by esterification and binds to two phosphate residues. This forms a chain of repeating phosphate–sugar bonds, to each of which a nucleic base is glucosidically bound to the sugar at the side. In addition to phosphoric acid and sugar, five different nucleic bases are available for building DNA and RNA. The two nitrogen bases adenine and guanine belong to the purine derivatives and the two nitrogen bases cytosine and thymine to the pirimidine derivatives. In RNA, thymine is exchanged for uracil, which is characterized by an additional CH3 group. The structural unit nitrogen base, sugar residue and phosphate residue is called nucleotide. In DNA, a double-helix structure is formed with two nucleic acid molecules joined together by hydrogen bonds to form a double strand. RNA consists of only one strand.
Function and purpose
Nucleic acid metabolism plays a major role in the storage and transmission of the genetic code. Initially, the genetic information is stored in DNA through the sequence of nitrogenous bases. Here, the genetic information for an amino acid is encoded by three consecutive nucleotides. The successive base triplets thus store the information about the structure of a particular protein chain. The beginning and end of the chain are set by signals that do not encode amino acids. The possible combinations of nucleic bases and the resulting amino acids are extremely large, so that, with the exception of identical twins, there are no genetically identical organisms. In order to transfer the genetic information to the protein molecules to be synthesized, RNA molecules are first formed. RNA acts as a transmitter of the genetic information and stimulates the synthesis of the proteins. The chemical difference between RNA and DNA is that the sugar ribose is bound in its molecule instead of deoxyribose. Furthermore, the nitrogen base thymine is exchanged for uracil. The other sugar residue also causes the lower stability and single-strandedness of the RNA. The double strand in the DNA secures the genetic information against changes. In this process, two nucleic acid molecules are linked to each other via hydrogen bonding. However, this is only possible with complementary nitrogen bases. Thus, DNA can only contain the base pairs adenine/thymine and guanine/cytosine, respectively. When the double strand splits, the complementary strand is always formed again. If, for example, a nucleic base is altered, certain enzymes responsible for repairing the DNA recognize the defect from the complementary base. The altered nitrogen base is usually replaced correctly. In this way, the genetic code is secured. Sometimes, however, a defect can be passed on resulting in a mutation. In addition to DNA and RNA, there are also important mononucleotides that play a major role in energy metabolism. These include, for example, ATP and ADP. ATP is adenosine triphosphate. It contains an adenine residue, ribose and the triphosphate residue. The molecule provides energy and converts to adenosine diphosphate when energy is released, splitting off a phosphate residue.
Diseases and disorders
When disorders occur during nucleic acid metabolism, diseases can result. For example, errors can occur in the construction of DNA, with an incorrect nucleic base being used. Mutation occurs. Changes to the nitrogen bases can occur through chemical reactions such as deamination. In this process, NH2 groups are replaced by O= groups.Normally, the complementary strand in the DNA still stores the code, so that the repair mechanisms can fall back on the complementary nitrogen base when correcting the error. However, in the case of massive chemical and physical effects, so many defects can arise that sometimes the wrong correction is made. In most cases, these mutations occur at less relevant sites in the genome, so that no effects are to be feared. However, if a defect occurs in an important region, it can lead to a serious change in the genetic material with massive effects on health. Somatic mutations are often the trigger of malignant tumors. Thus, cancer cells are formed every day. As a rule, however, these are immediately destroyed by the immune system. However, if many mutations form due to strong chemical or physical effects (e.g. radiation) or due to a defective repair mechanism, cancer can develop. The same applies to a weakened immune system. However, completely different diseases can also develop in the context of nucleic acid metabolism. When nucleic bases are broken down, pyrimidine bases give rise to beta-alanine, which is completely recyclable. Purine bases give rise to uric acid, which is difficult to dissolve. Humans must excrete uric acid through the urine. If the enzymes for recycling uric acid to build up purine bases are lacking, the uric acid concentration can increase to such an extent that uric acid crystals precipitate in the joints with the formation of gout.
