Question

1) How does being hydrophobic or hydrophilic affect the production and release, transport, and action or a hormone?

2) Is thyroxine hydrophilic or hydrophobic? How is that related to whether or not Amy could take it orally instead of injection.

Answer 1

1)

The hormones are two types-steroid or hydrophobic hormones and non steroid or hydrophilic hormones . The steroid hormones are derived from cholesterol and the non steroid hormones are like amines, peptides, polypeptides and proteins or glycoproteins that are derived from amino acids. The steroid or hydrophobic hormones are lipid soluble and can enter in any cell in the body but only the respective target cells respond to their activity. The lipid soluble steroid hormone molecules diffuse through the plasma membrane. They bind at a specific protein molecule or the receptor on the target cell. The hormone-receptor complex binds in the nucleus to a specific sequence of DNA in the target cell. This causes activation of transcription of specific genes and mRNA molecules are produced. The mRNA molecules are transported to the cytoplasm. The mRNA molecules are then translated in to the specific proteins. The newly synthesized proteins may act as enzymes, transport proteins or as hormone receptor and carryout the specific effect generated by the specific steroid hormone.

The non steroid or hydrophilic hormones like amines, peptides or proteins bind to the receptors on the target cell membranes. When the hormones bind to the receptors the receptors activity site interacts with the membrane proteins. The hydrophobic hormone binds to the receptor. The hormone-receptor complex activates the membrane proteins called G proteins. The G protein activates an enzyme or another membrane protein called adenylate cyclase. The activated adenyalte cyclase mediates the formation of cAMP from ATP in the cytoplasm. The cAMP further activates a group of enzymes called protein kinases. These enzymes transfer the phosphate groups from ATP to substrate molecules and this phenomenon is called phosporylation. The phosphorylation results in alteration in the shape of the substrate molecule and activate them. The activated proteins cause alteration in the cellular processes and bring about the characteristic effect of the hormone.

2)

The thyroxine is an amide hormone but is also lipid soluble. It can readily diffuse through plasma membrane or can be transported through ATP dependent carrier mediated transport mechanism. The thyroid hormone circulating in the blood binds with transport protein. The thyroxine or T4 is well absorbed by gut and hence canbe orally administered. The hydrophilic hormones cannot readily diffuse through cell membrane and readily absorbed. The thyroxine is hydrophobic or lipid soluble and hence readily diffuse through cell membrane. This impacts the absorption of hormone. Hence, the thyroxine can be taken orally as it is well absorbed by gut crossing the gut epithelium. Sometimes it is given as intravenous injection too.