Biochemistry Unit 11 General Principle of Hormone PDF

GENERAL PRINCIPLES OF HORMONES: BIOSYNTHESIS, METABOLSIM & MECHANISM OF ACTION BBM1233 MEDICAL BIOCHEMISTRY 2  Learning Objectives At the end of this lecture, the student will be able to: Compare the major chemical classes and the general mechanisms of hormones Describ...

GENERAL PRINCIPLES OF HORMONES: BIOSYNTHESIS, METABOLSIM & MECHANISM OF ACTION BBM1233 MEDICAL BIOCHEMISTRY 2  Learning Objectives At the end of this lecture, the student will be able to: Compare the major chemical classes and the general mechanisms of hormones Describe the mechanism of hormone action  HORMONES Hormones are produced and secreted into the blood stream by the endocrine glands. The circulatory system carries hormones to other parts of the body via the blood Hormones are chemical messengers responsible for coordinating certain body functions. In general they are stimulatory. Hormones: Mechanism of Signaling  Classes of Hormones Classes of hormones based on their solubility:  Classes of Hormones Classes of hormones based on chemical structure:  What Are Target Cells? Target cells refer to cells that contain specific receptors (binding site) for a particular hormone  Despite the molecular diversity of hormones, all hormone receptors can be categorized into one of two types, based on their location within the cell: Location of Receptor Principle Mechanism of Action Cell surface receptors Generation of second messengers (plasma membrane) which alter the activity of other molecules, usually enzymes, within the cell Intracellular receptors Alter transcriptional activity of (cytoplasm/nucleus) responsive genes  Hormones: Mechanism of Action Hormones with cell membrane receptors Water-soluble hormones have a hormone-binding site located on the external portion of a specific cell-surface receptor Hormones exert their action by binding to target cell receptor proteins Once binding take place, a conformation of the receptor protein conveys a signal to the interior of the cell Amplification of the hormone activity is achieved by activation of a cascade of chemical reactions  Hormones: Mechanism of Action Hormones with intracellular receptors Lipid-soluble (steroid) hormones diffuse easily through the lipid bilayer of cell membranes Receptors for these hormones are located in the cytoplasm, or in the nucleus of the target cell Binding causes a change in affinity of the receptor for binding sites on DNA in the cell nucleus Gene expression is changed by binding of the hormone- receptor complex to specific DNA binding sites Onset of action of lipid-soluble hormones is slow compared with water-soluble hormones and there is no amplification cascade  Regulation of Hormone Secretion Three types of stimuli that stimulates the synthesis & release of hormones:  Regulation of Hormone Secretion Regulation of hormone secretion normally maintains homeostasis & prevents overproduction or underproduction of a particular hormone Negative feedback (most common) Mechanisms that reverse the direction of a change in a physiological system Positive feedback Mechanisms that amplify physiological changes The change produced by the hormone causes more hormone to be released  Hormone Clearance Hormones are cleared from the plasma in several ways, including: 1. Binding with tissues 2. Metabolic destruction by the tissues (enzymes) 3. Excretion by the liver into the bile 4. Excretion by the kidneys into the urine