Question

The steroid hormone requires a protein carrier while being transported in the bloodstream and in the cytosol. Which features make it possible to pass through the membrane without the carrier?

A) The steroids tend to be large and water soluble and therefore can pass cell membranes.
B) Steroid hormones carry a charge and therefore enable the diffusion across membranes.
C) Steroid hormones are not soluble in water therefore they have an affinity for the lipids of the cell membrane.
D) Many large molecules can pass freely back and forth across cell membranes.

Answer 1

Steroid hormones are lipid-soluble and can pass directly through the plasma membrane to bind intracellular receptors due to their fat-soluble nature, while water-soluble hormones cannot and must rely on cell surface receptors to trigger a signaling pathway.

Step-by-step explanation:

Steroid hormones, which are lipid-soluble due to their composition of lipids such as phospholipids and cholesterol, can diffuse across the plasma membrane without the need for a carrier protein. These hormones are fat-soluble and can readily pass through the lipid bilayer of cell membranes because they have an affinity for lipids. Upon entering the target cell, steroid hormones bind to intracellular receptors in the cytoplasm or nucleus. This steroid-receptor complex then moves to the DNA and serves as a transcription factor to regulate gene expression. The protein products of these genes can alter cellular structure, produce enzymes, or regulate other cell functions.

The capacity of steroid hormones to diffuse through cell membranes is contrasted with water-soluble hormones, which cannot cross the lipid bilayer directly. Water-soluble hormones must bind to cell surface receptors and trigger a signaling pathway inside the cell to exert their effects. Unlike steroids, these hormones do not affect the DNA directly since they do not enter the cell.