AP BIOLOGY

Detailed explanation-1: -Which of the following signal molecules does not interact with cell surface receptors? Sol: (d) Testosterone.

Detailed explanation-2: -These intracellular receptors respond to small hydrophobic signaling molecules that are able to diffuse across the plasma membrane. The steroid hormones are the classic examples of this group of signaling molecules, which also includes thyroid hormone, vitamin D3, and retinoic acid (Figure 13.2).

Detailed explanation-3: -Answer and Explanation: Out of the molecules listed above, the one that is not involved in cell-to-cell signalling is option (d) cholesterol.

Detailed explanation-4: -Insulin is an example of a hormone whose receptor is a tyrosine kinase. The hormone binds to domains exposed on the cell’s surface, resulting in a conformational change that activates kinase domains located in the cytoplasmic regions of the receptor.