Genetic Code

The genetic code governs the production of protein synthesis in the cell by mapping DNA (deoxyribonucleic acid) sequences to proteins that are utilized for various cellular functions. The process of protein synthesis does vary between prokaryotes (single-cell organisms; i.e., cyanobacteria, E. coli) and eukaryotes (multicellular organisms; i.e., animal, plant); however, both cell types are characterized by the processes of transcription and translation that are mediated by the genetic code.

In the eukaryotic cell, chromosomes are located within the nucleus of the cell. These chromosomes contain DNA that are composed of sequence(s) of the basic unit of genetic information—the gene. Governed by noncoding and coding sequences, the gene plays an integral role in the encoding of proteins. The essential component of the gene is the segment or portion that is necessary for transcription to produce the RNA (ribonucleic acid) transcript, being the mRNA (messenger RNA), to serve as a carrier of genetic information from DNA to the ribosomes for the production of proteins.

Translation guides amino acid (protein building blocks) production by the sequence of nucleotide [Page 719]triplets, called codons, that stem from the RNA transcript. The RNA transcript is produced in the cell's nucleus and during this process three other types of RNA molecules are manufactured: tRNA (transfer RNA), rRNA (ribosomal RNA), and snRNA (small nuclear RNA). With the exception of snRNA, all RNA molecules eventually leave the nucleus via the nuclear pores and are involved in the process of translation that occurs mainly outside the nucleus. The snRNA are components of spliceosomes, which aid in removing introns (noncoding sequence) from the genetic sequence of DNA. The snRNAs interact with other subunit nuclear proteins to form these spliceosomes. The tRNA molecules are composed of 70 to 90 nucleotides that fold and are representative of another triplet nucleotide sequence, called the anticodons, that base pairs with complementary codons of the mRNA molecule on the ribosome for translation and the production of amino acids and the polypeptide chain—resulting in the synthesis of proteins. Thus, the “coding” defined by the triplet base pairing of codons and anticodons is instrumental for the production of a particular amino acid and subsequent protein.