Nucleic Acids

The Structure and Function of Nucleic Acids

DNA structure
DNA structure, from chromosome to deoxyribonucleic acid structure and base pairing. jack0m/DigitalVision Vectors/Getty Images

Nucleic acids are molecules that allow organisms to transfer genetic information from one generation to the next. There are two types of nucleic acids: deoxyribonucleic acid (better known as DNA) and ribonucleic acid (better known as RNA).

Nucleic Acids: Nucleotides

Nucleic acids are composed of nucleotide monomers linked together. Nucleotides contain three parts:

  • A Nitrogenous Base
  • A Five-Carbon Sugar
  • A Phosphate Group

Nucleotides are linked together to form polynucleotide chains. Nucleotides are joined to one another by covalent bonds between the phosphate of one and the sugar of another. These linkages are called phosphodiester linkages. Phosphodiester linkages form the sugar-phosphate backbone of both DNA and RNA.

Similar to what happens with protein and carbohydrate monomers, nucleotides are linked together through dehydration synthesis. In nucleic acid dehydration synthesis, nitrogenous bases are joined together and a water molecule is lost in the process. Interestingly, some nucleotides perform important cellular functions as "individual" molecules, the most common example being ATP.

Nucleic Acids: DNA

DNA is the cellular molecule that contains instructions for the performance of all cell functions. When a cell divides, its DNA is copied and passed from one cell generation to the next generation.

DNA is organized into chromosomes and found within the nucleus of our cells. It contains the "programmatic instructions" for cellular activities. When organisms produce offspring, these instructions in are passed down through DNA. DNA commonly exists as a double stranded molecule with a twisted double helix shape.

DNA is composed of a phosphate-deoxyribose sugar backbone and the four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In double stranded DNA, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C).

Nucleic Acids: RNA

RNA is essential for the synthesis of proteins. Information contained within the genetic code is typically passed from DNA to RNA to the resulting proteins. There are several different types of RNA. Messenger RNA (mRNA) is the RNA transcript or RNA copy of the DNA message produced during DNA transcription. Messenger RNA is translated to form proteins. Transfer RNA (tRNA) has a three dimensional shape and is necessary for the translation of mRNA in protein synthesis. Ribosomal RNA (rRNA) is a component of ribosomes and is also involved in protein synthesis. MicroRNAs (miRNAs) are small RNAs that help to regulate gene expression.

RNA most commonly exists as a single stranded molecule. RNA is composed of a phosphate-ribose sugar backbone and the nitrogenous bases adenine, guanine, cytosine and uracil (U). When DNA is transcribed into an RNA transcript during DNA transcription, guanine pairs with cytosine (G-C) and adenine pairs with uracil (A-U).

Differences Between DNA and RNA Composition

The nucleic acids DNA and RNA differ in composition. The differences are listed as follows:


  • Nitrogenous Bases: Adenine, Guanine, Cytosine, and Thymine
  • Five-Carbon Sugar: Deoxyribose


  • Nitrogenous Bases: Adenine, Guanine, Cytosine, and Uracil
  • Five-Carbon Sugar: Ribose

More Macromolecules

Biological Polymers - macromolecules formed from the joining together of small organic molecules.

Carbohydrates - saccharides or sugars and their derivatives.

Proteins - macromolecules formed from amino acid monomers.

Lipids - organic compounds including fats, phospholipids, steroids, and waxes.