Hormone Classes and Receptor Mechanisms - Anatomy and Physiology
- Epinephrine binds a Gs protein-coupled receptor on a liver cell. Which second messenger increases inside the cell?
- cAMP. The Gs protein activates adenylyl cyclase, which converts ATP to cAMP, and cAMP activates protein kinase A.
- Which type of receptor does insulin bind on its target cells?
- A receptor tyrosine kinase. Insulin binding causes the receptor to phosphorylate itself and downstream signaling proteins.
- From what precursor molecule are all steroid hormones synthesized?
- Cholesterol. Cortisol, aldosterone, estrogens and testosterone are all modified cholesterol molecules.
- Thyroid hormones are amines, but unlike catecholamines, where are their receptors located?
- Inside the cell, in the nucleus. T3 and T4 enter cells and, like steroids, act by changing gene transcription.
- Where are the receptors for steroid hormones located in target cells?
- Inside the cell, in the cytoplasm or nucleus. Lipid-soluble steroids diffuse through the plasma membrane to reach them.
- Why are steroid and thyroid hormones carried in the blood bound to plasma proteins?
- They are lipid-soluble and poorly soluble in plasma. Binding proteins transport them and lengthen their half-life.
- What is receptor down-regulation?
- A decrease in the number of target-cell receptors after prolonged exposure to high hormone levels, which reduces the cell's sensitivity to that hormone.
- Which amino acid is the precursor of both the catecholamines and the thyroid hormones?
- Tyrosine. Melatonin, the other common amine hormone, is derived from tryptophan instead.
- Why do peptide hormones bind receptors on the plasma membrane rather than inside the cell?
- They are water-soluble and cannot cross the lipid bilayer, so they act through membrane receptors that trigger intracellular signaling.
- What is signal amplification in a second-messenger hormone pathway?
- One hormone-receptor event activates many enzyme molecules, each making many products, so a tiny amount of hormone produces a large cellular response.
- How does a steroid hormone-receptor complex change the activity of a target cell?
- It binds DNA and alters gene transcription, changing which proteins the cell makes. This is why steroid effects begin slowly but last longer.
- To which chemical class of hormone does oxytocin belong?
- Peptide. Oxytocin is a nine-amino-acid peptide, so it is water-soluble and acts through a G protein-coupled membrane receptor.