Amino acids are the building blocks of proteins, macromolecules called polypeptides which have a variety of functions within the human body in the form of hormones, antibodies, and enzymes. Some proteins are structural including the ligaments, hair, and nails. Peptide biosynthesis, also called protein or peptide synthesis, refers to a succession of processes by which amino acids are linked through the formation of a chemical bond called a peptide bond, which eventually develops into a polypeptide. Once the protein has been synthesized, the gene for that particular type of protein is considered to be expressed, as each cell has deoxyribonucleic acid (DNA), genetic information necessary for manufacturing all protein needed by the body.
Gene expression has to do with the effect that DNA has on the phenotype, the biochemical or physical representation of genes in an individual such as hair or eye color. Brought about by a complex series of events, gene expression involves use of the information contained within the sequenced bases of DNA to specify the instructions for peptide biosynthesis. Proteins produced affect the phenotype, which can be readily observable physical traits or introduced as subtle chemical changes. The flow of information goes from DNA to ribonucleic acid (RNA) and finally into a protein.
Transcription is the first phase of gene expression, which accomplishes RNA molecule synthesis that is complementary to the DNA. RNA synthesis is determined by the DNA template through base-pairing, such that A always pairs with U, and G always pairs with C. A, U, G, and C represent the nucleotide bases adenine, uracil, guanine, and cytosine, respectively. This stage happens inside of the cell's nucleus and is referred to as transcription because it solves the problem of taking DNA information and transcribes it into another type of nucleic acid, messenger RNA (mRNA).
The core event of peptide biosynthesis and the second step of gene expression is translation, a process in which the mRNA is utilized as a coded message to direct peptide biosynthesis. Occurring in the cytoplasm of the cell, translation takes place in several steps: initiation, elongation, and termination. Information transcribed is used to determine the amino acid sequencing of the polypeptide. Yet another type of ribonucleic acid is used, referred to as RNA transferase (tRNA), necessary for moving the amino acids to the ribosomes in their coded order. Three consecutive nucleotide bases referred to as codons in mRNA determine one type of amino acid and is called a triplet code. Codons UGA, UAA, and UAG are only termination codes. All of the codons and instructions together encompass the genetic code.