Signal Transduction Pathways

1. Signal Transduction Pathways Prepared by: Samaneh Rahamooz Haghighi

2. Introduction • Cell-to-cell communication is essential for organisms • In multicellular organisms, cell-to-cell communication allows the cells of the body to coordinate their activities • Communication between cells is also essential for many unicellular organisms • Biologists have discovered some universal strategies and mechanisms of cellular regulation • Response is determined by combined effects of multiple signals • The plasma membrane plays a key role in most cell signaling • Pathway similarities suggest that ancestral signaling molecules evolved in prokaryotes and were modified later in eukaryotes(Alberts et al., 2002) • Signaling systems is similar in plants and bacteria (Campbell and Reece, 2008) 2

3. The Evolution of Cell Signaling Signaling systems is similar in plants and animals NO, c AMP, c GMP Scientists think that signaling mechanisms first evolved in ancient prokaryotes and single-celled eukaryotes 3

4. (Campbell and Reece, 2008) 4 Communication between yeast cells

5. Local and Long-Distance Signaling Eukaryotic cells may communicate by direct contact Animal and plant cells have junctions that directly connect the cytoplasm of adjacent cells These are called gap junctions (animal cells) and plasmodesmata (plant cells) The free passage of substances in the cytosol from one cell to another is a type of local signaling(growth factor) • Direct cytoplasmic connections: • - gap junctions in animal cells • - plasmodesmatain plant cells • -contact of surface molecules (cell-to-cell)recognition via receptors 5

6. (Campbell and Reece, 2008) 1- Gap junction 2- Cell-cell recognition 3- local regulators Communication between cells by direct contact 6

7. Plasmodesmata in plant cells 7

8. In many other cases of local signaling, messenger molecules are secreted by a signaling cell These messenger molecules, called local regulators, travel only short distances One class of these, growth factors, stimulates nearby cells to grow and divide This type of local signaling in animal cells is called paracrine signaling 8

9. Signaling pathway Paracrine Synaptic endocrine 9

10. In many other cases, cells must share information with cells they are not touching • They use (1) local regulators, messenger molecules that travel only short distances (Alberts et al., 2002) 10

11. Local signaling Target cell Secreting cell Secretory vesicle Local regulator diffuses through extracellular fluid. (a) Paracrine signaling 11

12. Local regulators – nearby cells paracrine signaling – only includes cells of a particular organ synaptic signaling – between neurons 12

13. Another more specialized type of local signaling occurs in the animal nervous system This synaptic signaling consists of an electrical signal moving along a nerve cell that triggers secretion of neurotransmitter molecules These diffuse across the space between the nerve cell and its target, triggering a response in the target cell neurotransmitter 13

14. Electrical signal along nerve cell triggers release of neuro- transmitter. Local signaling Neurotransmitter diffuses across synapse. Target cell is stimulated. 14 (b) Synaptic signaling

15. Long distance nerve transmission endocrine signaling 15

16. And (2) chemicals called hormonesfor long-distance signaling • In long-distance signaling, plants and animals use chemicals called hormones • In hormonal signaling in animals (called endocrine signaling), specialized cells release hormone molecules that travel via the circulatory system • Hormones vary widely in size and shape (Alberts et al., 2002) 16

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18. A Preview Earl W. Sutherland discovered how the hormone epinephrine acts on cells E. W. Sutherland studied the relationship between epinephrine presence and activation of glycogen phosphorylaseenzyme Sutherland suggested that cells receiving signals undergo three processes Reception Transduction Response 18

19. Generic Pathway • Reception – Chemical message (ligand) docks at receptor on cell membrane and changes its shape • Transduction – switching message from chemical signal received on cell outside to chemical messages on interior of cell • Response – Signal transduction cascade occurs until end result is reached 19

20. There are three stages in cell signaling • Reception • Transduction • Response CYTOPLASM EXTRACELLULAR FLUID Plasma membrane Reception Transduction Response 1 2 3 Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signaling molecule 20

21. Reception, the Binding of a Signaling Molecule to a Receptor Protein The binding between a signal molecule (ligand) and receptor is highly specific Ligand binding generally causes a shape change in the receptor A shape change in a receptor is often the initial transduction of the signal Many receptors are directly activated by this shape change Most signal receptors are plasma membrane proteins Hormones NO, CO 21

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