Growth and Developmental Hormones as Chemical Messengers
Hormones are a most appropriate topic for a meeting dealing with physical and chemical means of information transfer in living systems. The word HORMONE is often used to denote circulating chemical messengers, although we realise that not all chemical messengers need be circulating. For example, local hormones or neurotransmitter substances, such as acetylcholine, serotonin, noradrenaline, etc., act very near the site where they are produced without having to be transported via the circulatory system. Similarly, a very important group of most recently discovered substances called pheromones, which are used for communication between individual organisms, are transmitted through the air and impinge on the brain via the olfactory system. Most plant hormones, such as auxins, gibberellic acid, dormins, etc., do not need to be transported from one part of the plant to another. It is only in higher animals that hormones are made in very specialized organs, called endocrine glands, and these hormones can only reach their target tissues if appropriately carried to them in blood or other extracellular fluids.
KeywordsTyrosine Aminotransferase Chemical Messenger Amino Acid Incorporation Template Activity Urea Cycle Enzyme
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