Why Is the Sequence of Nitrogen Bases Important?

Nitrogen Bases

• All genetic information is encoded using guanine, cytosine, adenine, thymine and uracil. Guanine and adenine are called purines, having a larger double-ring atomic structure. Cytosine, thymine and uracil are called pyrimidines, featuring a smaller single-ring atomic structure. Thymine is found in deoxyribonucleic acid (DNA), while uracil takes its place in ribonucleic acid (RNA). These nitrogen bases combine with pentose, a five-carbon sugar, and phosphate to form nucleotides.

DNA and RNA Structure

• DNA and RNA represent chains of nucleotides. These bases are grouped into triplets, called codons, and are the foundations for amino acids or control functions. A total of 64 possible combinations (4 x 4 x 4) of codons are possible, representing 61 amino acid codons and 3 termination codons. The 61 amino acid codons specify 20 amino acids, the building blocks of life. Sequences serve as the blueprint for manufacturing a given protein. For instance, the protein insulin consists of a chain of 51 amino acid codons, representing 17 different amino acids. The termination codons signal the end of a protein code.

Protein Synthesis

• Living organisms must manufacture proteins in order to survive. The process begins with the creation of a copy of a section of DNA, called messenger RNA. This mRNA represents a blueprint for building one or more proteins. When a cell needs to synthesize a protein, the mRNA containing the corresponding protein code exits the nucleus and links with a ribosome. Ribosomal RNA forms the construction site, or factory structure. Transfer RNA reads the mRNA and delivers the proper amino acid, as defined by the codon sequence. The rRNA then bonds these amino acids together, producing the protein chain.

The Genetic Numbers

• Human cells contain 23 pairs of chromosomes, each representing a strand of DNA. Each strand of DNA contains billions of nucleotide bases. These nucleotides represent the genetic code for producing an estimated 30,000 to 75,000 different proteins. Each individual protein code represents a gene, and can consist of more than 38,000 codons, or 114,000 nucleotide bases. For example, the longest known protein in the human body, called titin or connectin, contains a chain of 38,138 amino acids -- each consisting of three nucleotide bases. The functionality of the incredibly large and complex human genetic system depends entirely on the exact sequence of the starting five nitrogen bases.