The document discusses various types of signal transduction in cells. It describes how extracellular signals like hormones bind to cell surface receptors and trigger intracellular signaling pathways using second messengers. These pathways involve G proteins and the production of molecules like cyclic AMP and inositol triphosphates to activate enzymes like protein kinase A and C. This leads to changes in gene expression, metabolism and cell behavior in response to extracellular signals.

1. Presented By- Manish Kumar Department of Pharmacology Mangalayatan university

5. Direct Contact Signaling a) Gap junctions They provide for metabolic cooperation between adjacent cells, and may help maintain homeostasis in connected cells for ion balance. Some signal molecules may move through gap junctions

6. b) Cell-cell recognition : Many signal molecules remain bound to surface of signaling cell & influence only cell that contact it. Important during development & immune responses.

10. The stages of chemical cell signaling 1. Reception The target cell must be able to detect that a signal is "arriving". This requires a chemical binding to a receptor molecule (protein), specialized for different functions. Most receptor molecules are found on the cell surface, but there area also intracellular receptors.

12. 3. Response The cell makes an appropriate response to the signal. A signal can activate enzymatic activity, genetic transcription, movement of cytoskeletal components, or other cell activities. Cell signals ensure that the right kind of activity occurs in the cell at the right time and in the proper cell conditions.

18. Structure of G-Protein

19. Signal transduction:- Trimeric G-Protein disassemble to Relay signals from G-Protein-Linked Receptors:-

24. Cyclic-AMP-dependent Protein Kinase (PKA) Mediates Most of the Effects of Cyclic AMP:-

25. How gene transcription is activated by a rise in cyclic AMP concentration?

41. It was found that in intact gastric mucosa, the changes in extracellular [Ca 2+ ] secondary to carbachol-induced increases in intracellular [Ca 2+ ] were sufficient and necessary to elicit alkaline secretion and pepsinogen secretion, independent of intracellular [Ca 2+ ] changes. These findings suggest that extracellular Ca 2+ can act as a "third messenger" via Ca 2+ sensor(s) to regulate specific subsets of tissue function previously assumed to be under the direct control of intracellular Ca 2+ .

44. Extracellular cAMP is hypothesized to have direct actions on putative receptor proteins (as of yet unidentified) that are expressed on neighboring cells. Alternatively, it is well established that extracellular cAMP can be sequentially metabolized, first by ectophosphodiesterase to adenosine monophosphate (AMP), and then by ecto-5'-nucleotidase to adenosine. Adenosine can then act as a paracrine or autocrine messenger to activate other signal transduction cascades via one of four subtypes of adenosine receptors (A 1 , A 2A , A 2B , A 3 ). In addition, since cAMP is relatively stable in blood, circulating cAMP can be converted by ectoenzymes at a distant site, effectively rendering cAMP as a prohormone for adenosine (which has a fleeting half-life in the circulation).