Describe the biochemistry of hormones. How hormones help control biochemical reactions in the target cell?

In terms of their chemical structure, hormones can be grouped into two general classes:

i)    lipid, or steroid, hormones

ii)       hormones derived from amino acids.

Steroid hormones, which include the sex hormones, are lipid molecules the body makes from cholesterol. Most invertebrate neurosecretory cells produce polypeptides called neuropepfides. Hormone: derived from amino acids include amino hormones, modified versions of single amino acids; peptide hormones, short chains of amino acids (as few as three); protein hormones; and glycoproteins..

In the target cells hormones help control biochemical reactions in three ways:

1. A hormone can increase the rate at which other substances enter or leave the cell;

2 It can stimulate a target cell to synthesize enzymes, proteins, cr other substances; or

3.         It can prompt a target cell to activate or suppress existing cellular enzymes

What is difference between negative and positive feedback?

Negative feedback is a primary mechanism of homeostasis, whereby a change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation.

Positive Feedback is a physiological  control mechanism in which a change in some variable triggers mechanisms that amplify the change. Fig.3.3.

Figure 3.3

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