Chapter 11 Cell Communication

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

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

15. 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.

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

17. 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.

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

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

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

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

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

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

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

27. 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.

28. 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.

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

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

32. 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+.

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

35. 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

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

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

39. 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.

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

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

43. 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.

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

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

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

49. Bethany Sullivan High School

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