Question

Why do purines pair with pyrimidines?

Answer 1

Hint: Deoxyribonucleic acid (DNA) is a molecule made up of two polynucleotide chains that coil around each other to create a double helix and carry genetic instructions for all known organisms and viruses' formation, function, growth, and reproduction. Nucleic acids include DNA and ribonucleic acid (RNA). Nucleic acids are one of the four primary types of macromolecules that are required for all known forms of life, alongside proteins, lipids, and complex carbohydrates (polysaccharides).

Complete answer:
Purines and pyrimidines are two nitrogenous base families that make up nucleic acids, or the building blocks of DNA and RNA, respectively. A sugar-phosphate chain serves as the ‘backbone' of each DNA strand. A nitrogenous basis, made up of carbon and nitrogen rings, is attached to each of these sugars. The number of rings in a base determines whether it is a purine (two rings) or pyrimidine (three rings) (one ring). Purines on one strand of DNA establish hydrogen bonds with matching pyrimidines on the other strand of DNA to keep the two strands together, and vice versa.
This is known as base pairing and is the most critical function of DNA molecules. Base pairs can be easily separated because hydrogen connections are weaker than covalent interactions, facilitating replication and transcription. Because purines and pyrimidines constantly bind together — a process known as complementary pairing – the ratio of the two will never change within a DNA molecule. In other words, when it comes to purines and pyrimidines, one strand of DNA will always be the exact complement of the other. Chargaff's Rule is the name given to this phenomena after Irwin Chargaff, who was the first to observe it.
This complementary pairing happens due to the bases' relative sizes and the types of hydrogen bonds that may be formed between them (they pair more favourably with bases with which they can have the maximum amount of hydrogen bonds). Purine is divided into two types: adenine and guanine. Both of these may be found in DNA and RNA. There are three kinds of pyrimidines, but only one of them, cytosine, is found in both DNA and RNA. Uracil, which is RNA-only, and Thymine, which is DNA-only, are the other two. The number of hydrogen bonds between purines and pyrimidines is constantly consistent, as is the number of purines that pair with particular pyrimidines.
Two hydrogen bonds connect ADENINE and THYMINE (A::T).
GUANINE (G::C) forms three hydrogen bonds with CYTOSINE (G::C).

Note:
The number of adenines and thymines in a DNA molecule will always be equal. Guanines and cytosines are the same way. As a result, if you know the percentage of one nitrogen base in a DNA molecule, you can figure out the percentages of the other three as well – its complementary pair will have the same percentage, and the sum of the first pair subtracted from 100 percent and divided by two will give you the percentages of the other two bases. On the test, you should expect to be asked to compute something similar to this.