Final answer:
Testosterone, a steroid hormone derived from cholesterol, is hydrophobic and easily diffuses across the plasma membrane. It binds to intracellular receptors and influences gene expression, impacting various physiological and developmental functions.
Step-by-step explanation:
Testosterone is a steroid hormone derived from cholesterol. It is produced mainly in the testes by Leydig cells in males and in the ovaries in females, with a small amount also being produced by adrenal glands. Testosterone travels through the bloodstream mostly bound to proteins, such as Sex Hormone Binding Globulin (SHBG), but it can also travel freely in its unbound form. The action of testosterone in the cell begins once it diffuses across the cell's plasma membrane due to its hydrophobic nature.
Since cholesterol is a component of the plasma membrane and steroid hormones like testosterone share a structural similarity with cholesterol, testosterone readily enters the cells. Inside the cell, it binds with specific intracellular receptors. This hormone-receptor complex then enters the nucleus and directly acts on the DNA, influencing the expression of certain genes connected to its effects, such as muscle growth, bone density, and the development of secondary sexual characteristics.
Therefore, testosterone can influence cellular function by affecting gene expression, which has wide-ranging effects on the organism, from tissue growth and maintenance to behavioral changes.