9.6. Nucleic Acids

The other type of macromolecule that one would find in the acid insoluble fraction of any living tissue is the nucleic acid. These are polynucleotides. Together with polysaccharides and polypeptides these comprise the true macromolecular fraction of any living tissue or cell.

Nucleic acids are one of the main categories of macromolecules found in cells, alongside polysaccharides and proteins. They are classified as polynucleotides, which means they are large molecules composed of repeating units called nucleotides. These nucleotides form long chains that are essential for various functions in the cell.

Imagine a long train where each car represents a nucleotide. Just like a train connects different stations, nucleotides connect to form nucleic acids, which play crucial roles in the functioning of living organisms.

For nucleic acids, the building block is a nucleotide. A nucleotide has three chemically distinct components. One is a heterocyclic compound, the second is a monosaccharide, and the third a phosphoric acid or phosphate.

Nucleotides, the building blocks of nucleic acids, consist of three parts: a nitrogenous base (the heterocyclic compound), a sugar (either ribose or deoxyribose), and a phosphate group. The nitrogenous base can be adenine, guanine, cytosine, uracil, or thymine, each playing a different role within DNA and RNA structures.

Think of a nucleotide like a sandwich: the bread represents the sugar, the lettuce and tomato represent the phosphate group, and the protein filling represents the nitrogenous base. Each part is essential to create a complete, functional sandwich (nucleotide).

As you notice in Figure 9.1, the heterocyclic compounds in nucleic acids are the nitrogenous bases named adenine, guanine, uracil, cytosine, and thymine. Adenine and Guanine are substituted purines while the rest are substituted pyrimidines. The skeletal heterocyclic ring is called purine and pyrimidine respectively.

Nucleotides contain specific nitrogenous bases categorized into two types: purines (which include adenine and guanine) that have a double-ring structure, and pyrimidines (which include cytosine, uracil, and thymine) that have a single-ring structure. These bases pair in specific ways, forming the structure of DNA and RNA.

Imagine a game of musical chairs where adenine and thymine are a pair, just like cytosine and guanine. Each pairing follows specific rules, akin to how they must match perfectly to maintain stability in the molecular structure.

The sugar found in polynucleotides is either ribose (a monosaccharide pentose) or 2’ deoxyribose. A nucleic acid containing deoxyribose is called deoxyribonucleic acid (DNA) while that which contains ribose is called ribonucleic acid (RNA).

The difference between DNA and RNA lies in their sugar component: DNA contains deoxyribose, and RNA contains ribose. This small change significantly impacts the structure and function of these nucleic acids, with DNA serving primarily in genetic information storage, while RNA is crucial for protein synthesis.

Think of DNA as a hard drive that stores all the information of a computer, while RNA acts like a messenger that carries instructions from the hard drive to different parts of the computer to execute tasks.

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