Question

Stimulation of membrane protein receptors by binding to specific molecules is not responsible for a. the sense of smell. b. sweet taste sensations. c. sour taste sensations. d. bitter taste sensations.

Short answer

Stimulation of membrane protein receptors by binding to specific molecules is responsible for all of the given options (sense of smell, sweet taste sensations, sour taste sensations, and bitter taste sensations). Therefore, none of the options provided is the correct answer for the exercise.

Step-by-step solution

Understand the role of membrane protein receptors in the sense of smell

Membrane protein receptors are essential in the sense of smell (olfaction). When odor molecules enter the nose and reach the olfactory epithelium, they bind to specific membrane protein receptors on olfactory receptor neurons, which then generate nerve signals and transmit them to the brain, where they are processed as a sense of smell.

Understand the role of membrane protein receptors in sweet taste sensations

Like the sense of smell, taste sensations also depend on the binding of specific molecules to membrane protein receptors. In sweet taste sensations, molecules present in the food we eat, typically sugars, bind to specific protein receptors (T1R2 and T1R3) on the surface of taste receptor cells in the taste buds. This binding activates downstream signal transduction pathways, which generate nerve signals that eventually reach the brain and are interpreted as sweet sensations.

Understand the role of membrane protein receptors in sour taste sensations

Sour taste sensations, like sweet sensations, are also mediated by the binding of specific molecules (in this case, hydrogen ions) to membrane protein receptors present on taste receptor cells. Hydrogen ions released by sour substances can bind to and inhibit potassium channels or act through other receptors, such as otopetrin-1, in the taste receptor cells. These interactions activate a signaling cascade, and the generated nerve signals are transmitted to the brain, where they are processed as sour taste sensations.

Understand the role of membrane protein receptors in bitter taste sensations

Bitter taste sensations are also mediated by the binding of specific molecules, such as alkaloids, to membrane protein receptors on taste receptor cells. Bitter substances can bind to the T2R family of G-protein-coupled receptors, activating downstream signaling pathways and generating nerve signals that are eventually transmitted to the brain and interpreted as bitter sensations.

Identify the correct option

Now that we have discussed the role of membrane protein receptors in each of the given options (sense of smell, sweet taste sensations, sour taste sensations, and bitter taste sensations), we can conclude that stimulation of membrane protein receptors by binding to specific molecules is responsible for all of the given options (a, b, c, and d). Therefore, none of the options provided is the correct answer for the exercise.