1.4 Properties of Biological Macromolecules

Nucleic acids store and transmit biological information, primarily in the form of DNA and RNA. The basic building blocks of nucleic acids are nucleotide monomers, each consisting of a five-carbon sugar (which can be deoxyribose in DNA or ribose in RNA), a phosphate group, and a nitrogenous base. The four types of nitrogenous bases found in DNA are adenine (A), thymine (T), guanine (G), and cytosine (C). In RNA, uracil (U) replaces thymine. Nitrogenous bases pair specifically due to hydrogen bonding: adenine (A) forms two hydrogen bonds with thymine (T) in DNA, while guanine (G) forms three hydrogen bonds with cytosine (C). This specificity ensures accurate replication and transcription of genetic information. The sequence of these nucleotides encodes biological instructions. DNA is a double-stranded helix that stores long-term genetic information, while RNA is typically single-stranded and functions in protein synthesis and gene regulation. Purines and pyrimidines are the two categories of nitrogenous bases found in nucleic acids, which play a crucial role in storing genetic information. Purines, which include adenine (A) and guanine (G), are larger, double-ring structures, while pyrimidines, which include cytosine (C), thymine (T), and uracil (U), are smaller, single-ring structures. In DNA, purines always pair with pyrimidines to maintain the uniform width of the double helix: adenine (A), a purine, pairs with thymine (T), a pyrimidine, through two hydrogen bonds, while guanine (G), a purine, pairs with cytosine (C), a pyrimidine, through three hydrogen bonds. In RNA, uracil (U) replaces thymine and pairs with adenine. These specific pairings, driven by hydrogen bonding, are essential for the accurate replication and transcription of genetic material.