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Chapter 7 Cell Communication. Question? u How do cells communicate? u By “cellular” phones. u But seriously, cells do need to communicate for many reasons.

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Presentation on theme: "Chapter 7 Cell Communication. Question? u How do cells communicate? u By “cellular” phones. u But seriously, cells do need to communicate for many reasons."— Presentation transcript:

1 Chapter 7 Cell Communication

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

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

4 Cell Communication

5 Cell Signaling (C.S.) u Is a relatively “new” topic in Biology and AP Biology. u Appears to answer many questions in medicine. u 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 u The target cell’s detection of a signal coming from outside the cell. u May occur by: u u Direct Contact u u Through signal molecules

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

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

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

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

17 Receptor Molecules u Usually made of protein. u Change shape when bind to a signal molecule. u 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 u Plasma membrane receptor. u Works with “G-protein”, an intracellular protein with GDP or GTP.

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

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

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

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

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

27 Tyrosine-Kinase Receptors u Extends through the cell membrane. u 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.

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

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

32 Ion-channel Receptors u Protein pores in the membrane that open or close in response to chemical signals. u Allow or block the flow of ions such as Na + or Ca 2+.

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

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

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

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

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

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

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

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

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

46 Secondary Messengers u Examples - cAMP, Ca 2+, inositol trisphosphate (IP 3 )

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

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49 Bethany Sullivan High School

50 Calcium Ions u More widely used than cAMP. u Used as a secondary messenger in both G-protein pathways and tyrosine-kinase receptor pathways.

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52 Calcium Ions u Works because of differences in concentration between extracellular and intracellular environments. (10,000X) u Used in plants, muscles and other places.

53 Inositol Trisphosphate (IP 3 ) u Secondary messenger attached to phospholipids of cell membrane. u Sent to Ca channel on the ER. u Allows flood of Ca 2+ into the cytoplasm from the ER.

54 Start here Or Start here

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57 Cellular Responses u Cytoplasmic Regulation u Transcription Regulation in the nucleus (DNA --> RNA).

58 Cytoplasmic Regulation u Rearrangement of the cytoskeleton. u Opening or closing of an ion channel. u Alteration of cell metabolism.

59 Transcription Regulation u Activating protein synthesis for new enzymes. u Transcription control factors are often activated by a Protein Kinase.

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61 Question u If liver and heart cells both are exposed to ligands, why does one respond and the other not? u Different cells have different collections of receptors.

62 Alternate explanation

63 Comment u Chapter focused only on activating signals. There are also inactivation mechanisms to stop signals.

64 Summary u Don’t get bogged down in details in this chapter. Use the KISS principle. u Know - 3 stages of cell signaling. u Know - At least one example of a receptor and how it works (in detail).

65 Summary u Know - protein kinases and cascades (amplification) u Know – example of a secondary signal u Upcoming – link of cell signaling to hormones


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