Significance of signal transduction and its mechanism

1. Signal transduction

9. • The homeostatic adaptations an organism makes to a constantly
• changing environment are in large part accomplished
• through alterations of the activity and amount of proteins.
• Hormones provide a major means of facilitating these changes.
• A hormone–receptor interaction results in generation of an
• intracellular signal that can either regulate the activity of a select
• set of genes, thereby altering the amount of certain proteins
• in the target cell, or affect the activity of specific proteins,
• including enzymes and transporter or channel proteins. The

10. • The
• signal can influence the location of proteins in the cell and can
• affect general processes such as protein synthesis, cell growth,
• and replication, perhaps through effects on gene expression.
• Other signaling molecules—including cytokines, interleukins,
• growth factors, and metabolites—use some of the same general
• mechanisms and signal transduction pathways. Excessive, deficient,
• or inappropriate production and release of hormones
• and of these other regulatory molecules are major causes of
• disease. Many pharmacotherapeutic agents are aimed at correcting
• or otherwise influencing the pathways discussed in

11. • The
• signal can influence the location of proteins in the cell and can
• affect general processes such as protein synthesis, cell growth,
• and replication, perhaps through effects on gene expression.
• Other signaling molecules—including cytokines, interleukins,
• growth factors, and metabolites—use some of the same general
• mechanisms and signal transduction pathways. Excessive, deficient,
• or inappropriate production and release of hormones
• and of these other regulatory molecules are major causes of
• disease. Many pharmacotherapeutic agents are aimed at correcting
• or otherwise influencing the pathways discussed in

12. The target cell concept
• There are about 200 types of differentiated cellThere are about 200 types of
differentiated cells in humans.
• Only a few produce hormones, but virtually all of the 75 trillion
• cells in a human are targets of one or more of the over 50
• known hormones. The concept of the target cell is a useful way
• of looking at hormone action. It was thought that hormones
• affected a single cell type—or only a few kinds of cells—and
• that a hormone elicited a unique biochemical or physiologic
• action. We now know that a given hormone can affect several
• different cell types; that more than one hormone can affect a
• given cell type; and that hormones can exert many different
• effects in one cell or in different cells. With the discovery of
• specific cell-surface and intracellular hormone receptors, the
• definition of a target has been expanded to include any cell
• in which the hormone (ligand) binds to its receptor, whether
• or not a biochemical or physiologic response has yet beens in humans.

13. Determination of the concentration of
hormone at the target cell

14. Specificity and selectivity of hormone
receptors

15. Determination of the target cell
response

16. Hormonal involvement in response to
a stimulus

17. Signal generation
• The lipophilic group 1 hormones diffuse
through the plasma membrane of all cells but
only encounter their specific high affinity
receptor in target cells. These receptors can
be located in the cytoplasm or in the nucleus
of the target cell. The hormone receptor
complex undergoes an activation
reaction.receptor activation occurs by two
mechanisms.

18. Signal generation

19. The DNA sequence of several response
elements

20. Components of the hormone receptor-
g protein effector system

25. Role of inositol and diacylglycerol in
intracellular signalling