Cell Communication

1. Cell Communication

2. Cells communicate by generating, transmitting, and receiving chemical signals.

3. Signal transduction pathway • Process by which a signal on a cell’s surface is converted into a specific cellular response • Communication involves transduction of stimulatory or inhibitory signals from other cells, organisms or the environment • Occurs in both unicellular and multicellular organisms

4. Signal transduction pathways • Occurs in 3 steps • Reception: target cell detects signal (ligand) coming from outside of cell (binds with protein usually on cell surface) • Transduction: binding of signal molecule changes protein in some way causing a relay of message inside cell • Response: transduced signal triggers a specific cellular response

6. Evolution and Cell Communication • Cell communication processes reflect a shared evolutionary history. • Evidence from yeast and animals suggest that early versions of cell signaling mechanisms used today evolved from bacteria

7. Unicellular organisms • Signal transduction pathways influence how the cell responds to its environment • Examples:

8. Response to external signals by bacteria that influences cell movement

9. Use of pheromones to trigger reproduction and developmental pathways • Example: mating yeast cells

10. Quorum Sensing • Use of chemical messengers by microbes to communicate with other nearby cells and to regulate specific pathways in response to population density • allows one organism to influence the gene expression of other bacteria in close proximity • Regulates: biofilm formation, virulence, and antibiotic resistance

11. QUORUM SENSING

12. Multicellular Organisms • Signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole

13. Epinephrine stimulation of glycogen breakdown in mammals

14. Temperature determination of sex in some vertebrate organisms

15. DNA repair mechanisms

16. Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling

17. Direct Contact Cell to Cell Communication • Cells can communicate by transferring chemical messengers that target cells in close vicinity

18. Example of Direct contact • Immune cells interact by cell-cell contact, antigen presenting helpers (APCs), helper T cells and killer T Cells • T cells and antigens circulate within blood and detect specific invaders, they produce chemical signals to tell each other that the cells belong

19. Plasmodesmata (gap junctions) between plant cells that allow material to be transported from cell to cell

20. Plant immune responses • invading pathogen are deprived of nutrients because the plant sends signals to kill cell surrounding the region where the pathogen infected the plant. Plant also induces the production of antimicrobial proteins. • When herbivores start eating plant, cell sends chemical signals to other regions of the plant • Some chemicals can inhibit leaf digestion in the insect’s gut

21. Quorum Sensing • Social insects use it to determine where to nest

22. Morphogens in embryonic development

23. APOPTOSIS“Cell suicide” Why are “Death proteins“ present in inactive form?

24. Signal transduction pathways link signal reception with cellular response • Signaling begins with the recognition of a chemical messenger, a ligand, by a receptor protein • Different receptors recognize different chemical messengers, which can be peptides, small chemicals or proteins, in a specific one to one relationship • A receptor protein recognizes signal molecules, causing receptor protein’s shape to change, which initiates transduction of the signal

25. G protein linked receptors • Plasma membrane receptor • When GDP is bound, G protein is inactive • When GTP is bound, G protein is active

26. Ligand gated ion channels • Incoming IONS trigger the response

27. Receptor tyrosine kinases • Receptor for growth factor • KINASE: Protein that “phosphorylates” (adds a phosphate to) another molecule • TYROSINE KINASES: Proteins that form dimers. Tyrosine amino acid residues are active in transfer of phosphates to relay proteins • Remain ACTIVE as long as LIGAND is attached

29. Cell Communication Part 2

30. Neurons (Nerves) • Specialized cells to transmit nerve impulses from one part of body to another • 3 main parts • Dendrite (signal receiving end) • Cell body • Axon (signal sending end)

31. Many axons have a myelin sheath that acts as an electrical insulator. • Schwann cells, which form the myelin sheath, are separated by gaps of unsheathed axon over which the impulse travels as the signal propagates along the neuron

32. Synapses • junction between two neurons where messages are passed on by neurotransmitters

33. Resting neuron structure • Contain potassium (K+) ions inside neuron • Sodium (Na+) ions are outside plasma membrane and don’t normally pass inward

34. Polarized neuron • Inactive (not sending an impulse) • Inside of neuron negatively charged to compared to outside

35. Stimulated neuron- Depolarization • Na+ gates in membrane open and Na+ rushes into cell causing inside to be more positive than outside of cell which activates neuron to transmit an action potential

36. Action potential • nerve impulse which causes the axon to release a neurotransmitter into synapse that binds to next neuron stimulating it

37. Cell Repolarization • After action potential • K+ rushes out of cell causing the inside to become negative again • Must occur before neuron can send another nerve impulse

38. After repolarization • Na+/K+ pump • Pumps K+ into cell and Na+ out to restore cell to make it polarized again

39. Transmission of information via neurotransmitters between neurons occur across synapses and result in responses • Responses can be stimulatory or inhibitory • Epinephrine • Acetylcholine • Norepinephrine • Dopamine • Serotonin • GABA

41. YOUTUBE Video

42. The L

43. Signals released by one cell type can travel long distances to target cells of another type • Endocrine signals (hormones) are produced by endocrine cells that release signaling molecules, which are specific and can travel long distances through the blood to reach all parts of the body • Examples: • Insulin • Human growth hormone • Thyroid hormone • Testerone • Estrogen

44. Insulin