Which of the following hormone classes is not water soluble?
options:
a) protein/peptide
b) steroid
c) glycoproteins
d) amines
The correct answer and explanation is:
The correct answer is b) steroid.
Steroid hormones are not water-soluble. They are lipid-soluble and are derived from cholesterol. Due to their hydrophobic nature, steroid hormones are able to pass through the lipid membranes of target cells without the need for a transport protein. Once inside the cell, these hormones bind to intracellular receptors, which then influence gene expression by interacting with the DNA in the nucleus.
On the other hand, protein/peptide hormones, glycoproteins, and amines are water-soluble. Protein and peptide hormones, like insulin and growth hormone, are composed of chains of amino acids and cannot cross cell membranes easily. Instead, they bind to receptors on the cell surface, which activates intracellular signaling pathways. Glycoproteins, such as luteinizing hormone (LH), are similar in that they are made up of a protein backbone with carbohydrate groups attached, making them water-soluble as well. Lastly, amines, like adrenaline and thyroid hormones, are derived from amino acids. Some amines, such as thyroid hormones, are lipid-soluble, while others, like catecholamines, are water-soluble.
The difference in solubility between these hormones is important because it affects how they are transported in the bloodstream, how they interact with their target cells, and how they influence various physiological processes. Water-soluble hormones are typically carried in the blood plasma and require receptors on the cell surface, whereas lipid-soluble hormones like steroids can diffuse across cell membranes and bind to intracellular receptors.