Prior to cell division, a new copy of DNA must be built. And in order for our cells to make proteins, RNA must be created from the DNA template. How is this accomplished?

Nucleic acids are the vital genetic blueprint, messengers and builders of the cellular world, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) the genetic material of cells. But what are DNA and RNA actually made of and how are they built?

What Are DNA and RNA Made of?

Nucleotides are the building blocks of nucleic acids. Each nucleotide is a monomer of nucleic acid and consists of 3 portions:

• a pentose sugar (ribose)
• one or more phosphate groups
• one of five cyclic nitrogenous bases

Phosphate-Sugar Backbone

Nucleotides are linked together by covalent bonds between phosphate of one nucleotide and sugar of next. These linked monomers become the phosphate-sugar backbone of nucleic acids. Nitrogenous bases extending from this phosphate-sugar backbone like teeth of a comb.

The Nucleic Acid “Ladder”

Hydrogen bonds form between specific bases of two nucleic acid chains, forming a stable, double-stranded DNA molecule. The structure is analogous to a ladder, with the two deoxyribose-phosphate chains as side rails and the base pairs, linked by hydrogen bonds, forming the rungs.

How Are Nucleotides Put Together Into Nucleic Acids?

Nucleic acid synthesis is an anabolic polymerization process. Anabolic reactions build bigger molecules and require energy. Polymerization is the process of taking nucleotide monomers and putting them together into polymers (large molecules composed of many monomers).

These three-phosphate nucleotide building blocks of DNA and RNA bring their own energy for polymerization within their phosphate bonds, three of them. When the triphosphate bond of the nucleotide is broken, it contributes the energy required add another nucleotide to the growing nucleic acid.

What Do Nucleic Acids Do?

The three main activities that nucleic acids are involved in are:

1. Replication: The duplication of genetic material.
2. Transcription: Passing the genetic code of DNA onto RNA molecules.
3. Translation: RNA following DNA’s instructions for building proteins from amino acids.

Replication

Before a cell divides, it must make a copy of its DNA so that both parent and daughter cell have a complete copy of genetic information. This process of copying the double-stranded DNA molecule is called replication.

Transcription

This is the process by which a DNA sequence is copied to produce a complementary strand of RNA. In other words, it is the transfer of genetic information from DNA into RNA.

Translation

Ribosomes (which contain rRNA) make proteins from the messages encoded in mRNA. Proteins are polymers made of monomer units called amino acids.

Each three nucleotide group of the nucleic acid, called a codon, encodes one amino acid. This triplet code of genetic instructions for a polypeptide chain is ‘written’ in the DNA as a series of 3-nucleotide ‘words,’ and this is the genetic code.

More Information on Nucleic Acids

To learn more about nucleic acids, see the science website Science Prof Online or additional Suite101 articles, including Nucleotides & Nucleic Acids, Nucleic Acids: Gene Recognition and Nucleic Acid Function.

Sources

Bauman, R. (2005) Microbiology.

Park Talaro, K. (2008) Foundations in Microbiology.