Exploring the Structure and Mechanism of Plasma Membrane Receptors

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Write an essay including diagram/s to describe the structure and mechanism of action of one named integral plasma membrane receptor of your choice (80%). Include a discussion of how the protein interacts with the plasma membrane’s lipid bilayer (20%).

Receptors are protein molecules that receive chemical signals in the form of ligands and induce responses at cellular level. They are localized at the cell surface, in the cytoplasm or the nucleus, a result of protein trafficking depending on their amino acid sequences. Receptors are ligand-specific due to the unique structures of their binding sites which complement those of ‘their’ ligands which results in a very high affinity (and subsequently low Kd or dissociation constant) of receptors …show more content…

Using benzodiazepines as an example, the binding of this drug to the benzodiazepine site increases the affinity of the receptor to GABA by triggering a conformational change in the GABA binding site. Binding of two molecules of GABA (one at each site) is sufficient to induce chloride ion channel opening through the rotation of the five kinks that block the passage of chloride ion in addition to other conformational changes not yet known. A wide enough route is provided for the energetically favorable influx of chloride ion (∆G < 0) into the postsynaptic neuron due to the higher concentration of chloride ion in the synaptic cleft (extracellular) as well as the electrostatic attraction between the positively charged arginine or lysine at the entrance and the chloride ion, resulting in hyperpolarization or inhibitory postsynaptic potential (IPSP). This decrease in postsynaptic membrane potential (more negative) causes the generation of action potential less likely as the threshold is harder to be reached. This results in a sense of ‘calmness’ or …show more content…

Instead, they are constantly cycled repeatedly between the plasma membrane and cytoplasmic compartments. This process is known as receptor internalization, and is vital in controlling the availability of the GABAA receptors on postsynaptic membrane. Normally this occurrence happens after drug withdrawal. This down regulation mechanism is dependent on the rate of endocytosis of the receptors and the level of GABAergic compounds in the synapses. Recycling happens when the receptors internalized are reinstated into the plasma membrane, post-, peri- or extra-synaptically. Those failed to be reinstated will be sent to lysosome for degradation and replaced with newly assembled complexes via secretory

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