The biosynthesis of all hormones largely occurs in specialized cells usually present in endocrine glands, which have the genetic phenotype to permit the correct orderly production of the hormone in question. Chapter 2 describes the production of the steroid hormones, while Chapters 6,11, and 16 describe the biosynthesis of the thyroid hormones, epinephrine, and prostaglandins, respectively. The next section of this chapter will provide a general description of the biosynthesis of peptide and protein hormones.
Each of the over 125 protein and peptide hormones is biosynthesized in specific cells, whose phenotype results in the orderly operation of the processes of gene transcription and mRNA translation. Figure 1-8 summarizes the many steps involved with transcription and translation. In the field of molecular biology, complementary DNA (cDNA) cloning technology, rapid sequencing of DNA, the use of PCR (polymerase chain reaction) methodology to amplify rare DNA sequences, and the availability of immunological (highly specific monoclonal or polyclonal antibodies) and nucleic acid probes have all contributed enormously to the generation of our current understanding of these fundamental biological responses.
Genes for polypeptide hormones contain the information to generate the specific amino acid sequence of the hormone and the control elements upstream from the start of the transcriptionally active sequence. However, the old adage, "one gene for one protein," is no longer absolutely true. There are circumstances where one gene can encode information for multiple hormones or multiple copies of the same hormone (see the following).
Figure 1-9 compares the details of the gene for pro-corticotropin releasing hormone (CRH), where one
poly A polymerase poly A polymerase primary RNA transcript
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