Cell Communication In depth 

- SIGNAL TRANSDUCTION: the process where one type of signal is converted to another 

- many extracellular signals act via cell surface receptors to change the behavior of the cell 

    - the receptor protein activates one or more intracellular signaling pathways each mediate by a series of intracellular signaling molecules 

- types of cell communication include; neuronal, juxtracrine. paracrine, and endocrine

External signals are converted to responses within the cell 

- the three stages of cell signaling; 

    1. RECEPTION: the target cell's detection of a signal molecule coming from outside the cell; the receptor is normally a protein which is very specific and the change in shape is caused by its activation 

    2. TRANSDUCTION; the conversion of the signal to form that can trigger a specific cellular response 

    3. RESPONSE: the specific cellular response to the signal molecule

Each cell responds to a limited set of signals 

- the same signal molecule can induce different responses in different target cells 

-     RECEPTION: a signaling molecule binds to a receptor protein causing it to change shape 

- INTRACELLULAR RECEPTORS: inside the cytoplasm or nucleus. The signal molecule must cross the plasma membrane and must be hydrophobic (small and no charge) 

- PLASMA MEMBRANE RECEPTOR: bind to water soluble ligands (cannot pass through; large polar charged)

- G- PROTEIN COUPLED RECEPTOR: membrane receptor that works with the helps of a G- protein 

- specific signal molecules cause ligand gated ion channels in a membrane to open r close regulating the flow of specific ions, resulting in a change in cell activity ( they cannot get through the phospholipid layer

- TRANSDUCTION: cascades of molecular interactions relay signals from receptors to target molecules in the cell 

- phosphorylation cascades include enzymes called protein kinases that phosphorylate and activate proteins at the next level 

   - signal can be turned on by kinases and off by phosphates 

- many signaling pathways involve small nonprotein water-soluble molecules or ions called second messengers 

- second messengers can initiate a phosphorylation cascade

-  amplify response without increasing the number of signal molecules 

   - can only happen in transduction 

- RESPONSE:  cell signaling leads to regulation of transcription or cytoplasmic activities 

- many signaling pathways ultimately integrate protein synthesis by turning gens off or on in the nucleus 

- TRANSCRIPTION FACTOR: the final molecule in a signaling pathway

- in the cytoplasm, signaling pathways often regulate the activity of proteins rather than their synthesis 

   -ex: the final step in the signaling pathway may affect the activity of enzyme or cause cytoskeleton rearrangements

- APOPTOSIS: triggered by signals that activate a cascade of suicide proteins in the cells