Nucleotides are the building blocks of DNA and RNA, consisting of a five-carbon sugar, a phosphate group, and an organic base. There are five organic bases: adenine, cytosine, guanine, thymine, and uracil. Purine bases consist of two rings of atoms, while pyrimidine bases have only one ring of atoms. Specific base pairing between purine and pyrimidine bases is crucial for the stability of the DNA molecule, which is composed of two nucleotide strands that spiral together to form a double helix.
Nucleotides are complex molecules that form the building blocks of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Each nucleotide has three parts: a five-carbon sugar, a phosphate group, and an organic base. There are two variants of the sugar, depending on whether the nucleotide is found in a DNA or RNA molecule. Additionally, one of five different organic bases can be attached to each nucleotide: adenine, cytosine, guanine, thymine, or uracil. Cytosine, guanine and adenine are found in both RNA and DNA molecules, while thymine is only in DNA and uracil is only in RNA.
All five bases have a complex ring structure made up of carbon and nitrogen atoms. Due to the nitrogen atoms present in the ring, bases are also called nitrogenous bases. Each of the bases has a chemical structure that differs from the other four, which allows for specific base pairing between each of the bases.
The five bases can be divided into two groups based on the number of rings present in their chemical structure. Purine bases consist of two rings of atoms and pyrimidine bases have only one ring of atoms. The purine bases include adenine and guanine, while the pyrimidine bases are cytosine, thymine and uracil. When bases pair and bind together, purine bases bind only to pyrimidine bases. More specifically, adenine binds only to thymine or uracil and cytosine binds only to guanine.
This specific base pairing is very important for the stability of a DNA molecule, which is composed of two nucleotide strands that spiral together to form a double helix. The two strands are held together by hydrogen bonds between complementary bases on each strand. Adenine and thymine are linked by two hydrogen bonds, while guanine and cytosine are linked by three hydrogen bonds. Only these pairs are capable of forming the hydrogen bonds necessary to make the DNA molecule stable.
By binding only between purine bases and pyrimidine bases, the distance between the two strands remains uniform, adding further stability to the DNA molecule. When a purine base binds to a pyrimidine base, a double ring molecule binds to a single ring molecule. If a purine base were to bond with a purine base, then two double ring molecules would be attached, or if a pyrimidine base binds to a pyrimidine base, then two single ring molecules would be attached. If all of these binding scenarios occurred, the DNA molecule would bend in and out and be uneven, which would affect its overall structure and stability. Having a stable DNA molecule is critical to success, as it carries the genetic information for each organism.
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