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There are four main families of receptors: ligand-gated ion channels, G-protein coupled receptors, kinase-linked receptors and nuclear receptors.

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Introduction

Essay 2: There are four main families of receptors: ligand-gated ion channels, G-protein coupled receptors, kinase-linked receptors and nuclear receptors. Describe the main characteristics and mechanism of action of each of these four families using suitable examples in each case. Receptors are found either on cell membranes or within cells themselves. In the body, they act as sensing elements which bring about the chemical communications that co-ordinate for the various functions occurring in different cells within the body. Most drug receptors tend to be protein in structure where they bind endogenous ligands such as numerous hormones, transmitters and cytokines. The activity of the majority of drugs is determined by their ability to bind to a specific receptor. This is as drugs act through receptors by binding to them to either initiate or to block (prevent) a response. In order to do this a drug must be as close a mimic of the neurotransmitter as possible. A neurotransmitter consists of similar properties to that of a substrate when in an enzyme interaction, as it has a specific shape enabling it to fit into a receptor site, causing a pharmalogical response. ...read more.

Middle

remain together forming a complex functioning mainly to support ?-subunit. This family of receptors undergo a conformational change as the ligands bind to them. The G-protein is thus exposed decreasing the affinity of the G-protein for guanosine diphosphate (GDP). The now vacant binding site is occupied by guanosine triphosphate which is present in high concentrations in the cytoplasm. The ?-subunit dissociates from both the receptor and �-? complex diffusing into the membrane where it binds to the effector. This procedure is then de-activated by hydrolysis where the ?, �, ? trimer are reunited. G-protein coupled receptors are divided into five distinct families (A - E) where groups A - C are present in animals. Family A is the largest of the three and is known as the rhodopsin family. It consists of receptors for most amine neurotransmitters and neuropeptides. Family B is comprised of receptors for peptide hormones and is known as being the secretin/glucagons family. The smallest is family C which consists of the metabotroic glutamate and calcium-sensing receptors. If G-protein coupled receptors are exposed to their ligand for long periods of time they become less sensitive to it. ...read more.

Conclusion

They are situated in the nucleus obtaining a monomeric structure (single polypeptide), which are separated into three functional domains. They consist of receptors for hormones such as steroid and thyroid. In this type of family, the ligands are lilophilic compounds that are adequately lipid soluble to cross the membrane resulting in them binding to intracellular receptors. Consequently gene transcription is regulated as the intracellular proteins function as dimeric molecules. The dimmer molecules bind to hormone-responsive elements of the nuclear DNA and specific genes are either induced or repressed depending on the type of hormone molecule. This hence produces different physiological effects as a result of the protein synthesis patterns altering. Overall in conclusion the four super families of receptors discussed, consist of very different structural as well as functional properties. They nevertheless are still equally as important. It is crucial to grasp an understanding of these families and their mechanism of as drug receptor interactions are critically significant when making decisions concerning choosing a drug for treatment. This is because when doing so numerous characteristics need to be considered, such as whether a direct or indirect effect is needed to be achieved or the time course of drug action that needs to take place. ?? ?? ?? ?? 252 Pharmacology. ...read more.

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