Step by Step
Chol→
Cholesterol is the precursor for all steroid hormones
All steroid hormones are derived from cholesterol through a series of enzymatic modifications in the adrenal cortex, gonads, and placenta. The four-ring steroid backbone is conserved — only the side chains differ. Major classes: glucocorticoids (cortisol), mineralocorticoids (aldosterone), androgens (testosterone), estrogens (estradiol), progestogens (progesterone).
Lip
Lipid-soluble — cross membranes freely
Because steroid hormones are lipid-soluble (derived from cholesterol), they can diffuse directly across the plasma membrane without needing a receptor on the cell surface. They enter the cell and bind intracellular receptors in the cytoplasm or nucleus — unlike peptide hormones, which bind surface receptors.
Memory trick: Steroids are lipid = they slip through the lipid membrane. Peptide hormones are water-soluble = can't cross, must knock on the door.
NR
Nuclear receptors — gene expression changes
Once inside the cell, steroid hormones bind to nuclear receptor proteins. The hormone-receptor complex acts as a transcription factor — binding specific DNA sequences and activating or repressing gene transcription. This is slow (hours) but long-lasting — unlike the rapid effects of surface receptor signaling.
5
Five major classes to know
Glucocorticoids (cortisol): stress response, anti-inflammatory. Mineralocorticoids (aldosterone): Na⁺ reabsorption, blood pressure. Androgens (testosterone, DHEA): male sex characteristics. Estrogens (estradiol): female sex characteristics. Progestogens (progesterone): pregnancy maintenance.
Applied Walkthrough
1
Cortisol is released from the adrenal cortex during stress. Being lipid-soluble, it diffuses directly across the plasma membrane of target cells.
2
Inside the cell, cortisol binds the glucocorticoid receptor (GR) in the cytoplasm. The cortisol-GR complex translocates to the nucleus.
3
The complex binds glucocorticoid response elements (GREs) in DNA, activating transcription of anti-inflammatory genes and repressing pro-inflammatory genes.
4
Effect is slow to start (hours) but sustained. This explains why steroid drugs (prednisone) take time to work but have prolonged effects.
Exam Application
Exams test the lipid-soluble nature of steroid hormones (cross membranes freely), that they bind intracellular nuclear receptors (not surface receptors), and that their mechanism involves gene expression changes. Know the five classes and their primary hormones. The contrast with peptide hormones (water-soluble, surface receptors, fast signaling) is very frequently tested.
⚠ Common Trap
Students confuse steroid hormones with peptide hormones — steroids are lipid-soluble and bind intracellular receptors; peptides are water-soluble and bind surface receptors. Also: steroid hormone effects are SLOW (hours) because they require gene transcription and protein synthesis — not the rapid second-messenger signaling of peptide hormones.
✓ Quick Self-Check
1. What is the precursor for all steroid hormones?
Cholesterol — all steroid hormones are derived from cholesterol through enzymatic modifications.
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2. Why can steroid hormones cross the plasma membrane directly?
They are lipid-soluble (derived from cholesterol) and can diffuse through the lipid bilayer without needing a surface receptor.
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3. Where do steroid hormones bind inside the cell?
To nuclear receptor proteins in the cytoplasm or nucleus — the hormone-receptor complex then acts as a transcription factor.
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4. Name the five major classes of steroid hormones.
Glucocorticoids (cortisol), mineralocorticoids (aldosterone), androgens (testosterone), estrogens (estradiol), progestogens (progesterone).
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5. Why are steroid hormone effects slow to start but long-lasting?
They require gene transcription and protein synthesis — this takes hours but produces sustained changes in cell function.
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