Signal transduction mechanism

Introduction
Definition
History
Basic element in signal transduction
Basic Pathway of signal transduction
Types of signal transduction
Second messenger
Pathway of signal transduction
Conclusion
References

1. SIGNAL TRANSDUCTION   By KAUSHAL KUMAR SAHU Assistant Professor (Ad Hoc) Department of Biotechnology Govt. Digvijay Autonomous P. G. College Raj-Nandgaon ( C. G. )

2. Synopsis Introduction Definition History Basic element in signal transduction Basic Pathway of signal transduction Types of signal transduction Second messenger Pathway of signal transduction Conclusion References

3. INTRODUCTION Process of signal transduction involve ordered sequence of biochemical reaction inside the cell, which are carried out by enzymes, activates by second messengers, resulting in a signal transduction pathway . Cell signaling is a phenomenon in which information is relayed across the plasma membrane to the cell interior and often transmitted to the cell nucleus.

4. DEFINATION Signal transduction is a series of steps by which external stimuli are converted into chemical signals and then into cellular responses . A hormone bind to a specific receptor in plasma membrane. This stimulates the cell to produce second messenger which relay the hormonal signal to intracellular sites triggering(as a fire arm) the cells various responses to the original signal.

5. HISTORY In 1970 Martin Rod bell Firstly examined Signal Transduction, through effect of glucagons on a rat’s liver cell. glucagons + bind Guano sine triphosphate disassociated glucagons ↓ stimulates G- protein ↓ strongly influences the cell metabolism

6. Basic element in signal transduction 1- Ligand – An extra cellular molecule whether organic or inorganic which binds to receptor and there by alter its function is called ligand. E.g. ions, sugars, proteins. Also known as signals or first messenger. 2- Receptor :- Trans membrane protein that binds to the ligand. Receptor for secreted molecules (including protein, small peptides, amino acids, etc)

7. 3- Second messenger- second messenger , molecule inside cells that acts to transmit signals from a receptor to a target.

8. Modes of cell signaling Autocrine Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) That binds to autocrine receptors on that same cell, leading to changes in the cell.

9. Paracrine Paracrine signaling is a form of cell signaling in which the target cell is near ("para" = near) the signal-releasing cell.

10. Endocrine when cells need to communicate a message over a long distance, they can use the endocrine system. Endocrine signalling uses chemicals called hormones to send messages throughout the body.

11. Basic Pathway of signal transduction A-Reception : A cell detects a signaling molecule from the outside of the cell. A signal is detected when the chemical signal (also known as a ligand) binds to a receptor protein on the surface of the cell or inside the cell. B:Transduction : When the signaling molecule binds the receptor it changes the receptor protein in some way. This change initiates the process of transduction. C-Response : Finally, the signal triggers a specific cellular response.In the third stage of cell signaling, the transduction processes brings about a cellular response to the stimulus.

12. Types of signal transduction Extra cellular Signal Transduction Inter cellular Signal Transduction Intra cellular Signal Transduction

13. A) Extra cellular Signal Transduction Extra cellular signals are those come from out of the network and that gives some effect to the network via specific interaction with one of the molecules in the network. Most extra cellular chemical signals are water soluble and membrane impermeable. Example – Steroid hormones.

14. B) Inter cellular Signal Transduction – This type of signal transduction describes the mechanism by which one cell (sender cell) send a message to change the function of another cell (target cell). Two cells can communicate by two methods – Contact dependent signaling – This type of signaling requires direct physical contacts between sender cell and target cell. The second method involved release of secreted molecules from the sender cell to the target cell and does not requires direct contact between the sender cell and target cell .

15. C) Intra cellular Signal Transduction Intra cellular signal transduction is largely carried out by second messenger molecules . Intracellular signaling molecules in eukaryotic cell includes. heterotrimeric G-protein small GTPase, cyclic nucleotide , such as cAMP , cGMP and Ca2+ ion.

16. That is released into the interior of the cell following the binding of a first messenger – a hormone or other ligand – to a receptor at the outer surface of the cell. Cyclic AMP is synthesized by an integral membrane protein called adenylyl cyclase, whose catalytic resides at the inner surface of the plasma membrane. Cyclic AMP

17. Cyclic GMP Cyclic guanine monophosphate is known as Cyclic GMP. GTP by guanylyl cyclases and degraded to GMP by a phosphodiesterase. The action of cGMP is frequently mediated by activation of cGMP dependent protein kinases, although cGMP also regulates ion channels.

18. In vertebrate eye , it responsponsible for converting the visual signals received as light to nerve impulses. The photoreceptor in rod cells of the retina is a G protein-coupled receptor called rhodopsin.

19. C-IP3 Inositol trisphosphate or inositol, IP3 binds to and activates the InsP3 receptor on the membrane of the endoplasmic reticulum (ER)opens a calcium channel, resulting in the release of Ca2+ into the cytoplasm. Calcium ions (Ca 2+ ) and inositol trisphosphate (IP 3 ) function as second messengers in many signal transduction pathways.

20. Ca2+ Calcium (Inactive state) ↓ First messenger comes and binds to receptor ↓ This interaction induces a conformational change in proteins ↓ Protein specific to calcium channels open the channels for Ca ↓ Calcium ions exit from intracellular storage sites into the cytoplasm ↓ Calcium (active state) ↓ Carries message to the target site ↓ Triggers target site for response FUNCTION: Muscle contraction, vision in retina cells, proliferation of cells

21. Pathway of signal transduction Gated ion channels Cyclic nucleotide-gated ion channels Their function can be the result of a combination of the binding of cyclic nucleotides (cGMP and cAMP) and either a depolarization or a hyperpolarization event. Initially discovered in the cells that make up the retina of the eye, CNG channels have been found in many different cell types across both the animal and the plant kingdoms.

22. Enzyme-linked receptors - Binding of insulin of the α chain activates the tyrosin kinase activity of β chain and each α- β monomer phosphorylase 3 criticle tyrosin residuce near the terminal of β chain.

23. G proteins . Many extra cellular stimuli (first messengers) initiate responses by interacting with G- protein coupled receptors (GPCR) on the outer cell surface and stimulating the release of a second messenger within the cell. The signal is transmitted from the receptor to the effector by a heterotrimeric G- protein. These proteins are referred to as heterotrimeric because they have three subunits (α, β and γ) and as G proteins because they bind guanines either GDP or GTP.

24. Activation cycle of a G-protein (purple) by a G-protein-coupled receptor (light blue) receiving a ligand (red).

25. Conclusion Finally we conclude that signal transduction is a universal property of living cells, which is found in plant cell, wells as in unicellular cells. Animal cell exchange information about the concentration of ion and glucose in extracellular.

26. References THE CELL- A Molecular Approach- By M.Cooper & Robert E. Hausman (5 th Edition)S Text Book of cell Biology- By Karp Genetics- By B.D. Singh Website www.wikipedia.org/(8.45 pm)