Which of the following molecules could participate in cell signaling without a second messenger?

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11ecba2d_0e53_cbb4_a3bf_21e1a0ff9aa1_MD0008_00 Cells communicate with and respond to their environments through chemical signals. Chemical signals must be transmitted across the cell membrane to induce a response. Hydrophilic signal molecules such as peptide hormones interact poorly with the hydrophobic tails of phospholipid bilayers, so they cannot easily cross cell membranes. Instead, these hormones (first messengers) bind to cell surface receptors such as G-protein-coupled receptors. These receptors relay the signal by causing the production of new molecules, called second messengers, on the cytosolic side of the membrane. The second messenger molecules can then interact with proteins in the cytosol and nucleus, leading to a response. In contrast, hydrophobic molecules such as steroid hormones can cross the cell membrane and directly interact with effector proteins inside the cell. Therefore, these hormones do not require second messengers. Steroid hormones are derived from cholesterol and are easily recognized by their characteristic backbone structure, consisting of three 6-membered rings and one 5-membered ring fused together. The molecule in Choice B, estradiol, contains this characteristic backbone and is an example of a steroid hormone that signals without a second messenger. (Choice A) This molecule is folic acid, also known as vitamin B₉, which is not typically involved in signaling. The multiple nitrogen and oxygen atoms in the structure make it hydrophilic and unable to readily cross the cell membrane, so if it did signal it would require a second messenger. (Choice C) This molecule is the electron carrier NADH. The charged phosphate groups make it hydrophilic, so if NADH were involved in cell signaling it would require a second messenger. (Choice D) This structure is a polypeptide, and therefore it would act as a peptide hormone in signaling. Peptide hormones require second messengers. Educational objective: Cells communicate through chemical signals called hormones. Hydrophilic hormones such as peptide hormones cannot cross the cell membrane and require second messengers. Hydrophobic hormones such as steroid hormones can cross the cell membrane and do not need second messengers.

Which of the Following Molecules Could Participate in Cell Signaling