The three primary functions of genes are storing information, replication, and the accumulation of mutations. Proteins, also known as polypeptides, are polymers of amino acids linked by peptide bonds. Most genes carry the instructions for producing a single polypeptide and are expressed through a two-step process: transcription, which synthesizes an mRNA copy of the gene, followed by translation, where this mRNA is used to produce a protein. Translation occurs on ribosomes, the cell’s protein factories, and requires transfer RNAs (tRNAs), which act as adapters capable of recognizing both the genetic code in mRNA and the corresponding amino acids.
Translation elongation involves three key steps: (1) the transfer of an aminoacyl-tRNA to the A site, (2) the formation of a peptide bond between the amino acid at the P site and the aminoacyl-tRNA at the A site, and (3) the translocation of mRNA by one codon length through the ribosome, positioning the newly formed peptidyl-tRNA at the P site. Translation concludes at a stop codon (UAG, UAA, or UGA). A segment of RNA or DNA that includes a translation initiation codon, a coding region, and a termination codon is referred to as an open reading frame. The section of mRNA between its 5'-end and the initiation codon is called the leader or 5'-UTR, while the part between the 3'-end (or poly(A) tail) and the termination codon is referred to as the trailer or 3'-UTR.
DNA replicates through a semiconservative mechanism: as the parental strands separate, each serves as a template for the synthesis of a new complementary strand. A mutation in a gene often leads to a change in the corresponding position within the polypeptide product. Sickle cell disease serves as an example of the harmful effects such mutations can cause.