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Chapter 11 Cell Communication

Chapter 11 Cell Communication. Question?. How do cells communicate? By “cellular” phones. But seriously, cells do need to communicate for many reasons. Why do cells communicate?. Regulation - cells need to control cellular processes.

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Chapter 11 Cell Communication

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  1. Chapter 11Cell Communication

  2. Question? • How do cells communicate? • By “cellular” phones. • But seriously, cells do need to communicate for many reasons.

  3. Why do cells communicate? • Regulation - cells need to control cellular processes. • Environmental Stimuli - cells need to be able to respond to signals from their environment.

  4. Cell Communication

  5. Cell Signaling (C.S.) • Is a relatively “new” topic in Biology and AP Biology. • Appears to answer many questions in medicine. • Is a topic you’ll be hearing more about in your future.

  6. Stages of C.S. 1. Reception - receiving the signal. 2. Transduction - passing on the signal. 3. Response - cellular changes because of the signal.

  7. Reception

  8. Transduction

  9. Response

  10. Reception • The target cell’s detection of a signal coming from outside the cell. • May occur by: • Direct Contact • Through signal molecules

  11. Direct Contact • When molecules can flow directly from cell to cell without crossing membranes. • Plants - plasmodesmata • Animals - gap junctions

  12. Direct Contact • May also occur by cell surface molecules that project from the surface and “touch” another cell.

  13. Signal Molecules • The actual chemical signal that travels from cell to cell. • Often water soluble. • Usually too large to travel through membranes. • Double reason why they can’t cross cell membranes.

  14. Signal Molecules • Behave as “ligands”: a smaller molecule that binds to a larger one.

  15. Receptor Molecules • Usually made of protein. • Change shape when bind to a signal molecule. • Transmits information from the exterior to the interior of a cell.

  16. Receptor Mechanisms 1. G-Protein linked 2. Tyrosine-Kinase 3. Ion channels 4. Intracellular

  17. G-protein linked • Plasma membrane receptor. • Works with “G-protein”, an intracellular protein with GDP or GTP.

  18. G-protein • GDP and GTP acts as a switch. • If GDP - inactive • If GTP - active

  19. G-protein • When active (GTP), the protein binds to another protein (enzyme) and alters its activation. • Active state is only temporary.

  20. G-protein linked receptors • Very widespread and diverse in functions. • Ex - vision, smell, blood vessel development.

  21. G-protein linked receptors • Many diseases work by affecting g-protein linked receptors. • Ex - whooping cough, botulism, cholera, some cancers

  22. G-protein linked receptors • Up to 60% of all medicines exert their effects through G-protein linked receptors.

  23. Tyrosine-Kinase Receptors • Extends through the cell membrane. • Intracellular part functions as a “kinase”, which transfers Pi from ATP to tyrosine on a substrate protein.

  24. Mechanism 1. Ligand binding - causes two receptor molecules to aggregate. Ex - growth hormone 2. Activation of Tyrosine-kinase parts in cytoplasm. 3. Phosphorylation of tyrosines by ATP.

  25. Intracellular Proteins • Become activated & cause the cellular response.

  26. Tyrosine-Kinase Receptors • Often activate several different pathways at once, helping regulate complicated functions such as cell division.

  27. Ion-channel Receptors • Protein pores in the membrane that open or close in response to chemical signals. • Allow or block the flow of ions such as Na+ or Ca2+.

  28. Ion-channel Receptors • Activated by a ligand on the extracellular side. • Causes a change in ion concentration inside the cell. • Ex - nervous system signals.

  29. Intracellular Signals • Proteins located in the cytoplasm or nucleus that receive a signal that CAN pass through the cell membrane. • Ex - steroids (hormones), NO - nitric oxide

  30. Intracellular Signals • Activated protein turns on genes in nucleus.

  31. Comment • Most signals never enter a cell. The signal is received at the membrane and passed on. • Exception - intracellular receptors

  32. Signal-Transduction Pathways • The further amplification and movement of a signal in the cytoplasm. • Often has multiple steps using relay proteins such as Protein Kinases.

  33. Protein Phosphorylation • The addition of Pi to a protein, which activates the protein. • Usually adds Pi to Serine or Threonine.

  34. Protein Kinase • General name for any enzyme that transfers Pi from ATP to a protein. • About 1% of our genes are for Protein Kinases.

  35. Amplification • Protein Kinases often work in a cascade with each being able to activate several molecules. • Result - from one signal, many molecules can be activated.

  36. Secondary Messengers • Small water soluble non-protein molecules or ions that pass on a signal. • Spread rapidly by diffusion. • Activates relay proteins.

  37. Secondary Messengers • Examples - cAMP, Ca2+, inositol trisphosphate (IP3)

  38. cAMP • A form of AMP made directly from ATP by Adenylyl cyclase. • Short lived - converted back to AMP. • Activates a number of Protein Kinases.

  39. Bethany Sullivan High School

  40. Homework • Read Chapter 11, 45 • Lab – Cells – drawings due • Chapter 11 – Wed. 10/3

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