Video Transcript
Hormones can be broadly classified
into steroid and nonsteroid hormones. Which of the following statements
correctly describes a difference between the mechanism of action of the two
types? (A) Nonsteroid hormones are lipid
soluble and can pass through target cell membranes, whereas most steroid hormones
are not and must bind to receptors on cell surface membranes. Or (B) steroid hormones are lipid
soluble and can pass through target cell membranes, whereas most nonsteroid hormones
are not and must bind to receptors on cell surface membranes.
Hormones are chemical messengers
that travel throughout an organism’s body, usually through the blood, to have an
effect on target cells. There are two main types of
hormones that function slightly differently to cause effects: steroid hormones and
nonsteroid hormones.
Steroid hormones are derived from
lipids, and so they are lipid soluble. This means that steroid hormones
can diffuse directly across the phospholipids in the cell surface membrane of target
cells, moving directly into the cytoplasm. There, steroid hormones can bind to
steroid hormone receptors, which can either be found in the cytoplasm, in the
nucleus, or sometimes in other organelles, such as the endoplasmic reticulum or
mitochondria. The steroid–hormone receptor
complex that is formed usually allows a specific gene to be transcribed, eventually
forming a useful protein, which will have a specific function.
Nonsteroid hormones are derived
from amino acids and are hydrophilic so are not lipid soluble. This means that these hormones
cannot directly pass the phospholipids that form the cell surface membrane of their
target cells. Instead, nonsteroid hormones must
bind to nonsteroid hormone receptors found on the cell surface membrane of their
target cells. This activates a series of
reactions within the cell, eventually leading to a cellular response.
Now that we know the difference
between the mechanism of action of steroid hormones and nonsteroid hormones, we can
answer the question correctly. The correct answer is (B). Steroid hormones are lipid soluble
and can pass through target cell membranes, whereas most nonsteroid hormones are not
and must bind to receptors on cell surface membranes.
