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.  Environmental Stimuli - cells need to be able to respond to signals from their environment.

Cell Communication How?

Direct Contact  May also occur by cell surface molecules that project from the surface and “ touch ” another cell. How?

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

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.

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

Reception

Transduction

Response

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

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.

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

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.

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

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

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

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

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.

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

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 Ca 2+.

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

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

Intracellular Signals  Activated protein turns on genes in nucleus.

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

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.