Question

Different chemical precursors are used in the synthesis of hormones.

a) What are the 3 main categories of hormones in a chemical sense?

b) What advantages does this different chemical nature of hormones provide in terms of how hormones act at their target cells?

************ Please leave a detailed description to part 2. Thank you :)

Answer 1

a. Three main chemical categories of hormones are

1.lipid derivatives/ steroids: examples: estrogen,progerterone ,cortisol.

2.peptide hormones:eg. Insulin, parathormone

3.amino acid derivatives:eg. epinephrine, melatonin,T3 ,T4.

b.Most water-soluble hormones, like the amino acid derivatives and peptides, can travel freely in the blood because they "like" water. However, they are repelled by lipid or fatty structures such as the membranes that surround the cell and nucleus. Because of this, these hormones generally bind to receptor sites on the outside of the cell and signal from there.

Fat-soluble hormones, like the sex hormone steroids estrogens and androgens, are fat soluble and water repellent. That is, they "like" lipid or fatty structures such as those surrounding cells but are generally repelled by watery areas. Steroids generally travel to their target cells attached to a special carrier protein that "likes" water (such as, sex steroid hormone binding globulin and serum albumin). The hormones detach before passing into the cell where they bind to receptors.

To get a better picture of this, think of oil and water. The two don't mix and separate into distinct layers. In this case, the amino acid derived and peptide hormones would prefer to be in the water layer, and the steroid hormones would prefer to be in the oil layer. Special carrier proteins that are comfortable in both oil and water can escort the peptide and amino acid derived molecules into the oil, and the steroid molecules into the water.

☆☆Peptide hormones have receptors on cell surface therefore they binds with G protein coupled receptors and require second messenger for signal transduction and hence consists of slower action.

whereas steroids binds directly to nuclear receptor and hence quick onset of action.

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