1. Cell Communication
Chapter 9

2. Overview
Communication between cells requires these basic steps: sending, receiving, signal transducing, responding
Ligand – signaling molecule
Receptor protein – molecule to which the receptor binds
Interaction of these two components initiates the process of signal transduction, which converts the information in the signal into a cellular response

4. There are four basic mechanisms for cellular communication
Direct contact
Paracrine signaling
Endocrine signaling
Synaptic signaling
Some cells send signals to themselves (autocrine signaling)

5. Direct contact
Molecules on the surface of one cell are recognized by receptors on the adjacent cell
Important in early development
Gap junctions

6. Paracrine signaling
Signal released from a cell has an effect on neighboring cells
Signaling between immune cells
Coordinates clusters of neighboring cells
Important in early development

7. Endocrine signaling
Hormones released from a cell travel through circulatory system to affect other cells throughout the body
Both animals and plants use this mechanism extensively

8. Synaptic signaling
Animals
Nerve cells release the signal (neurotransmitter) which binds to receptors on nearby cells
Association of neuron and target cell is a chemical synapse

9. Signal transduction
Events within the cell that occur in response to a signal
When a ligand binds to a receptor protein, the cell has a response

10. Receptor Types Receptors can be defined by their location
Intracellular receptor – located within the cell
Cell surface receptor or membrane receptor – located on the plasma membrane to bind a ligand outside the cell
Transmembrane protein in contact with both the cytoplasm and the extracellular environment

12. Intracellular Receptors
Steroid hormones
Common nonpolar, lipid-soluble structure
Can cross the plasma membrane to a steroid receptor
Binding of the hormone to the receptor causes the complex to shift from the cytoplasm to the nucleus
Act as regulators of gene expression (turning it on or off)

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15. Insulin receptor
Activated receptor has sites that allow docking
Insulin is a hormone that helps to maintain a constant blood glucose level
Lowers blood glucose

16. **Cell-to-Cell Interactions
Cells can identify each other by cell surface markers
Different receptors can produce the same messengers
Hormones glucagon and epinephrine can both stimulate liver cells to mobilize glucose
Different signals, same effect
Both act by same signal transduction pathway

18. Existence of multiple forms (isoforms) of the same receptor
Single signaling molecule can have different effects in different cells
Existence of multiple forms (isoforms) of the same receptor
Receptor for epinephrine has 9 isoforms
Encoded by different genes
Sequences are similar but differ in their cytoplasmic domains
Different isoforms activate different proteins leading to different signal transduction pathways