A base pair consists of two nucleobases that face each other in deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), bind to each other, and form the double strand with the help of hydrogen brϋcken. This is the genomic information of an organism and includes the genes. Incorrect base pairing can lead to mutations.
What is base pairing?
A base pair is made up of nucleobases. This is an element of DNA or RNA. These nucleobases, in turn, together with phosphoric acid or phosphate and deoxyribose, a sugar, form the nucleotide (the base). The phosphoric acid and the deoxyribose are the same for each nucleotide; they form the backbone of DNA. The base and the deoxyribose are called the nucleoside. The phosphate residue fϋresults in the DNA being negatively charged and also hydrophilic, an interaction with water occurs. Nucleotides differ only in the base. There are fϋnf bases, depending on whether they are components of DNA or RNA. The bases are adenine (A) and guanine (G), these belong to the purines. Thymine (T), cytosine (C) and uracil (U) are pyrimidines. Purines are heterocyclic organic compounds, while pyrimidines are heterocyclic aromatic organic compounds. In DNA, base pairing occurs between adenine and thymine (A-T), and guanine and cytosine (G-C). In RNA, on the other hand, base pairing occurs between adenine and uracil (A-U), and between guanine and cytosine (G-C). This base pairing is called complementary. The pairings are created by hydrogen brϋcking. This is the interaction between a hydrogen atom with a free electron pair of another atom. The hydrogen atom is covalently bonded in this case. This is a chemical bond in which there is an interaction between the valence electrons from one atom and the nucleus of another atom. Base pairing is also used as a measure of size for DNA: 1bp corresponds to one and 1kb corresponds to 1000 base pairs or nucleotides.
Function and task
Base pairing has essential functions fϋr the structure of DNA. DNA occurs as a double helix. In this case, the spatial arrangement of the double helix is referred to as B-DNA, a right-handed double-stranded helix that has a more relaxed arrangement in contrast to the A-form. Base pairing of adenine and thymine results in the formation of two hydrogen brϋcks. In contrast, the base pairing of guanine and cytosine results in the formation of three hydrogen bridges. Due to the base pairing between a purine and a pyrimidine, the resulting distance between the two DNA strands is always the same. This results in a regular structure of the DNA, where the diameter of the DNA helix is 2nm. A complete rotation of 360° within the helix occurs every 10 base pairs and is 3.4 nm long. Base pairing also plays an important role in DNA replication. DNA replication is divided into initiation phase, elongation phase and termination phase. This occurs during cell division. The DNA is unwound by an enzyme, DNA helicase. The double strands are separated and a DNA polymerase attaches to a DNA single strand and begins to make a complementary DNA strand on each single strand. This creates two new DNA single strands, which form a new DNA double helix. The complementary base pairing ensures the structure of the newly synthesized DNA double helix. In addition, base pairing plays an essential role in protein biosynthesis. This is divided into transcription and translation. During transcription, the DNA double helix is unwound and the complementary strands are separated from each other. This is also done by the enzyme helicase. RNA polymerase binds to a single strand of DNA and forms complementary RNA. In RNA, uracil is used instead of thymine and, compared to DNA, it has a so-called polyA tail. RNA always ends in a string of adenines. RNA also remains a single strand and serves to synthesize a protein during translation. The type of protein depends on the particular gene that was read and used as a template for protein biosynthesis.
Diseases and disorders
Erwin Chargaff found that the number of bases adenine and thymine as well as guanine and cytosine is 1:1.James D. Watson and Francis Harry Compton Crick eventually found that there is complementary base pairing of adenine and thymine as well as guanine and cytosine. This is called Watson-Crick pairing. However, unusual base pairing can occur due to various disorders, such as reverse Watson-Crick pairing. Another faulty from of base pairing is wobble pairing. These are pairings contrary to Watson-Crick pairing, such as G-U, G-T, or A-C. These errors can occur during DNA replication and must then be eliminated by DNA repair. Mutations can occur as a result of faulty base pairing. These mutations do not have to be harmful. There are so-called silent mutations, in which a base pair is exchanged with another pair, but it does not result in any functional or structural disturbances for the synthesized protein. However, in the case of sickle cell anemia, a mutation is the reason for the formation of non-functional red blood cells. The mutation directly affects hemoglobin, which is responsible for oxygen transport in the blood. Severe and life-threatening circulatory disorders and anemia result.
