Gene expression is the process by which genetic instructions are used to synthesize gene products. These products are usually proteins, which go on to perform essential functions as enzymes, hormones and receptors, for example. Genes that do not code for proteins such as ribosomal RNA or transfer RNA code for functional RNA products.
Genes are subunits of DNA, the information database of a cell that is contained inside the cell nucleus. This DNA carries the genetic blueprint that is used to make all the proteins the cell needs. Every gene contains a particular set of instructions that code for a specific protein.
DNA exists in the form of two long, paired strands that form a double helix. Each of these strands is made up of individual building blocks called nucleotide bases. These bases include adenine, thymine, cytosine, and guanine (A, T, C and G), which are arranged in triplets, with each triplet representing a specific amino acid.
DNA is found in all cells present in the body aside from those that do not contain a nucleus such as mature red blood cells or the cornified cells of nails and skin. Each human cell is made up of 46 chromosomes, each of which contains highly condensed and coiled DNA consisting of millions of gene sequences. In each cell, 23 chromosomes are inherited from the father and 23 are inherited from the mother. Twenty-two of the chromosomes from each parent are autosomes and the remaining chromosome is an X or Y sex chromosome.
Gene structure and gene expression in higher organisms
Reviewed by Sally Robertson, BSc Further Reading