Steroid Hormones

Steroid hormones are soluble in the lipids that make up the bulk of cell membranes. For this reason, steroid hormones can easily diffuse into their target cells. Once inside a target cell, steroid hormones combine (usually within the nucleus) with specific protein receptors. The resulting hormone-receptor complex binds within the nucleus to a particular region of the DNA and activates specific genes. The activated genes, in turn, are transcribed into messenger RNA (mRNA), which enters the cytoplasm where it directs synthesis of specific proteins. These proteins bring about the cellular changes associated with the particular hormone (fig. 13.4, table 13.3, and Clinical Application 13.1). An example is the steroid hormone aldosterone (al'do-ster-on", al-dos'ter-on), from the adrenal gland, whose action is to stimulate sodium retention by the kidneys. In response to aldosterone, cells that form tubules within the kidney begin to synthesize more Na+/K+ pumps, the proteins that actively

Steroid Hormones Cells

ure m

Figure

^Hormone-receptor t complex ure m

Figure

(a) A steroid hormone passes through a cell membrane and (b) combines with a protein receptor, usually in the nucleus. (c) The hormone-receptor complex activates messenger RNA synthesis. (d) The mRNA leaves the nucleus and (e) guides protein synthesis. Note: In the bloodstream, most lipid-soluble steroids are bound to proteins. Only the few that are not bound are free to enter cells, as shown here.

(a) A steroid hormone passes through a cell membrane and (b) combines with a protein receptor, usually in the nucleus. (c) The hormone-receptor complex activates messenger RNA synthesis. (d) The mRNA leaves the nucleus and (e) guides protein synthesis. Note: In the bloodstream, most lipid-soluble steroids are bound to proteins. Only the few that are not bound are free to enter cells, as shown here.

1. Endocrine gland secretes steroid hormone.

2. Steroid hormone diffuses through target cell membrane and enters nucleus.

1. Endocrine gland secretes steroid hormone.

2. Steroid hormone diffuses through target cell membrane and enters nucleus.

3. Hormone combines with a receptor molecule.

4. Steroid hormone-receptor complex binds to DNA and promotes transcription of messenger RNA.

5. Messenger RNA enters the cytoplasm and directs protein synthesis.

6. Newly synthesized proteins produce hormone's specific effects.

transport these ions across the cell membrane, retaining sodium.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment