Chapter 11 Cell Communication

1. Chapter 11Cell Communication

2. You Must Know • 3 stages of cell communication • Reception, transduction, & response • How G-protein-coupled receptors receive cell signals & start transduction • How receptor tyrosine kinase receive cell signals & start transduction • How a cell response in the nucleus turns on genes while in the cytoplasm it activates enzymes • What apoptosis means & why it is important to normal functioning of multicellular organisms

3. 11.1 • External signals are converted into responses within the cell • Animal cells communicate: • by direct contact • by secreting local regulators (growth factors or neurotransmitters)

4. 3 stages of cell signaling: • 1) Reception: • The target cell’s detection of a signal molecule coming from outside the cell • 2) Transduction: • Conversion of the signal to a form that can bring about a specific cellular response • 3) Response: • Specific cellular response to the signal molecule

6. 11.2 • Reception: a signal molecule binds to a receptor protein, causing it to change shape • The binding between a signal molecule (LIGAND) & a RECEPTOR is highly specific • A change in the shape is the initial transduction of the signal

7. Receptors are found in 2 places: • 1) Intracellular • Inside membrane in the cytoplasm or nucleus • Signal molecule MUST cross the membrane (hydrophobic) : examples – steroids & NO • 2) Plasma membrane receptors • Bind to water-soluble ligands

8. 3 types of plasma membrane receptors: • 1) G-Protein-Coupled receptor • 2) Receptor tyrosine kinase • 3) Ligand-gated ion channels

9. 1) G-Protein-Coupled receptor • Step 1 • The ligand (signaling molecule) has bound to the G-protein-coupled receptor • Causes a conformational change in the receptor so it can bind to an inactive G-protein • This causes a GTP to displace the GDP • This activates the G-protein • Step 2 • The G protein binds to a specific enzyme & activates it • When activated, it triggers the next step in a pathway leading to cellular response • All shape changes are temporary • To continue, new molecules are required

11. 2) Receptor tyrosine kinase • Step 1 • Shows binding of signal molecules to the receptors & formation of a dimer • Each tyrosine kinase adds a phosphate from an ATP • Step 2 • Fully activated receptor protein that initiates a unique response • The ability of a single ligand to activate multiple responses is the difference between #2 & #1

13. 3) Ligand-gated ion channels • Caused by specific signal molecules • Opens & closes to regulate the flow of specific ions - Na+ or Ca2+

15. 11.3 • Transduction – Multiple molecular interactions relay signals from receptors to target molecules • Involve a phosphorylation cascade • Usually a multistep pathway • Leads to greater amplifying of the signal • Enzymes called protein kinases phosphorylate & activate proteins • Allows for a greater cellular response

17. Not all components are proteins • May include small, nonprotein water-soluble molecules or ions called SECOND MESSENGERS • Calcium ions & cyclic AMP are examples • Once activated, they can initiate a phosphorylation cascade

18. 11.4 • Response – Cell signaling leads to regulation of transcription or cytoplasmic activities • Many pathways regulate protein synthesis • Done by turning specific genes on or off in the nucleus • The final activated molecule in a signaling pathway functions as a transcription factor

19. In the cytoplasm • Signaling pathways often regulate the activity of proteins rather than their synthesis • Example: final step in signaling pathway may affect the activity of enzymes or cause cytoskeleton rearrangement

20. 11.5 • Apoptosis – integrates multiple cell signaling pathways • Controlled cell suicide • The cell is systematically dismantled & digested • Protects neighboring cells from damage that would occur if a dying cell leaked out its enzymes

21. Apoptosis • Triggered by signals that activate a cascade of suicide proteins in the cells • In vertebrates, a normal part of development: • Normal nervous system • Operation of immune system • Normal morphogenesis of hands & feet in humans