Genes and Proteins
Since the rediscovery of Mendel’s work in 1900, the definition of the gene has progressed from an abstract unit of heredity to a tangible molecular entity capable of replication, transcription, translation, and mutation. Genes are composed of DNA and are linearly arranged on chromosomes. Genes specify the sequences of amino acids, which are the building blocks of proteins (Figure 1). In turn, proteins are responsible for orchestrating nearly every function of the cell. Both genes and the proteins they encode are absolutely essential to life as we know it.
Replication, Transcription, and Translation are the three main processes used by all cells to convert a gene into a protein. In eukaryotic cells, or those cells that have a nucleus, replication and transcription take place within the nucleus while translation takes place outside of the nucleus in the rough endoplasmic reticulum. In prokaryotic cells, or those cells that do not have a nucleus, all three processes occur in the cytoplasm.
Replication, a biological process that occurs in all living organisms, copies their DNA; it is the basis for biological inheritance. In this process, DNA polymerase copies one double-stranded DNA molecule into two double-stranded DNA molecules. Transcription is the process in which RNA polymerase creates a complementary mRNA copy of a sequence of DNA. Translation is the process by which messenger RNA (mRNA) is decoded and translated by the ribosome to produce a polypeptide sequence, otherwise known as a protein.