A nucleotide is a basic building block of ribonucleic acid (RNA) or deoxyribonucleic acid (DNA) that has a base, sugar, or phosphate component. In cells, nucleotides have vital functions and are involved in hormonal signal transduction or energy production, for example.
What are nucleotides?
Nucleotides are the basic building blocks of RNA and DNA. They are composed of a sugar molecule, a specific base, and a phosphate group. Nucleotides are used in the genetic code, and many types, such as GTP, cAMP, and ATP, also perform vital cellular functions. The giant molecules RNA or DNA consist of a total of five different nucleotide species.
Function, effect and tasks
Nucleotides are very important for the formation of new cells as well as energy metabolism and also function as messenger substances. Without nucleotides, a body could not function. With the help of nucleotides, the organism can restore its function after diseases or injuries. This requires many building materials and a lot of energy, which, however, are not available in sufficient quantities in the case of a lack of nucleotides. In general, then, nucleotides perform the following functions in the body:
- Energy carrier: this requires the anhydride bonds, which are very high in energy.
- Precursors of synthesis products such as RNA and DNA.
- Parts of coenzymes: these are important for the course of various chemical reactions.
- Allosteric modulatory function: nucleotides have the task to regulate the activity of key enzymes
Formation, occurrence, properties and optimal values
A nucleotide consists of the following components:
- A monosaccharide composed of 5 C atoms, also known as pentose.
- A phosphoric acid residue and
- From one of the total of five nucleobases (uracil, thymine, cytosine, guanine, adenine).
The sugar is thereby linked to the base and phosphorus. When phosphate is attached to a nucleoside, the formation of the simplest nucleotide, called a mononucleotide, occurs. Under water splitting, the phosphate forms an ester bond with the 5-C atom of the nucleoside. Therefore, nucleotides are very often called “phosphate esters of nucleosides”. If further phosphate residues are added, nucleoside di- or nucleoside triphosphates are formed. Phosphoric anhydride bonds are formed between the phosphates, which have a great deal of energy. In DNA, only thymine, cytosine, guanine and adenine, respectively, are used, whereas in RNA, uracil is present instead of thymine. There are also a number of other bases that are called rare bases because they are present in nucleic acids only in very small amounts. These include, for example, hydroxylated or methylated purine as well as pyrimidine bases such as pseudouridine, dihydrouracil or 5-methylcytosine. Three nucleotides linked together form the smallest unit necessary to encode genetic information in RNA or DNA. This unit of information is called a codon. Basically, two types of nucleotides are distinguished: pyrimidine nucleotides and purine nucleotides. Purine nucleotides have a heterocyclic ring system consisting of two rings, whereas pyrimidine nucleotides have only one ring. Nucleotides are a natural component of animal and plant food and are found in all cells. The polymeric nucleic acids ingested with food are degraded by the organism to nucleotides or nucleosides, which are subsequently absorbed in the small intestine. However, nucleic acids occur in food in varying amounts. Offal has a very high proportion, but meat and fish also contain many nucleic acids.
Diseases and disorders
Healthy people are able to absorb sufficient amounts of nucleotide compounds from food, recycle them from cells, or synthesize them endogenously. However, if the endogenous supply is insufficient, then it is extremely important to consume nucleotides in the diet. In particular, tissues that have a high energy requirement need nucleotides in sufficient quantities. These include, for example, the intestines, the liver, the immune system, the muscles and the nervous system. Chronic diseases occur particularly often in these tissues.Other tissue types such as the brain, lymphocytes, erythrocytes or leukocytes cannot synthesize nucleotides and are also dependent on supply via certain foods. In certain disease states or when nucleotide uptake is reduced, dietary nucleotides are recommended to optimize tissue function. Dietary nucleotides stimulate bifidobacteria growth. Furthermore, lesions in the gastrointestinal tract can also be reduced and the length or growth of intestinal villi increased. Particularly in children who grow very quickly, in the case of major injuries or infections, the question arises as to whether the self-synthesis is sufficient to cover an increased nucleotide requirement. Breast milk contains a relatively high proportion of nucleotides, so infants who are fed breast milk should also have an appropriate supply. If the nucleotide sequence of genes changes, this is called a mutation. For example, one nucleotide pair in the DNA may be replaced by another. In this case, one speaks of a point mutation or a “silent mutation”. If one or more nucleotide pairs are lost or pairs are inserted, either a deletion or an insertion occurs within a gene. In many cases, the protein formed then has a completely different structure and is unable to perform its functions. Mutations can either be caused by mutagenic substances or radiation, or they can occur spontaneously. As a result, individual bases can be altered and DNA can be damaged.
