| Hormones may be simple or complex, and may have very different chemical structures
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Many different types of molecules function as hormones (Table 37.1). At the simplest level, modified amino acids , such as epinephrine (adrenaline), have hormonal activity. Other hormones are polypeptides, synthesized on the ribosome, and vary in size from a tripeptide (e.g. thyrotropin releasing hormones, TRH) up to complex glycoproteins (e.g. luteinizing hormone, LH). The smaller peptide hormones are synthesized as larger polypeptide or protein pre- or pro-hormones, then are cleaved by specific proteolytic enzymes to release the active hormone from the endocrine gland. Other hormones are derived by modification of simple lipids such as cholesterol or fatty acids. Some of these molecules require further metabolism within their target cell before they can exert their full biological effect (e.g. the conversion of circulating testosterone to its active form dihydrotestosterone).
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| Figure 37.1 Basic endocrine processes. The feedback regulation of hormone action is a classical example of self-regulation. |
| Figure 37.2 The sandwich design for enzyme-linked immunosorbent assay (ELISA) for the measurement of hormone concentration. The amount of signal present on the microplate after washing of the serum/reagents is a measure of the concentration of a hormone. |
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