1. Cell Communication Chapter 11 11/17/2018 11:51 PM
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2. YOU MUST KNOW
The 3 stages of cell communication: reception, transduction, and response
How a receptor protein recognizes signal molecules and starts transduction
How a cell signal is amplified by a phosphorylation cascade
An example of a second messenger and its role in a signal transduction pathway
How a cell response in the nucleus turns on genes, whereas in the cytoplasm it activates enzymes
What apoptosis means and why it is important to normal functioning of multicellular organisms

3. 3 stages of cell signaling
Reception – the target cell detects a signal molecule coming from outside the cell
Transduction – the signal is converted to a form that can bring about a specific cellular response
Response – the cell responds in a specific way

4. Reception Ligand & Receptor Ligand is the signal molecule
Receptor is what it binds to
Very specific – think lock & key again
Often a conformational change in receptor when ligand bind (think induced-fit model of enzymes)

5. Types of Receptors
Intracellular receptors – found in the cytoplasm or nucleus
Requires that the signal molecule crosses the cell membrane – means it must be hydrophobic
Ex. steroid hormones
Plasma membrane receptors – membrane proteins
Bind water-soluble ligands

6. G-protein coupled receptors
Membrane receptor that works with the help of a G protein
Inner membrane proteins that bind GDP/GTP

7. Ligand binds to GPCR which causes a conformational change to the receptor
Enables receptor to bind an inactive G protein
Results in GTP losing a phosphate - exergonic reaction that provides energy and results in GDP
These events activate the G protein

8. 2. The G protein binds to an enzyme (specific!) and activates it
This triggers the next step in the pathway which leads to a cellular response
*All conformational changes are temporary – in order for response to continue, new ligand molecules are required

10. Receptor tyrosine kinases
2-part membrane proteins

11. Ligand bonds to receptor
Results in the formation of a dimer (molecular complex in which two identical molecules are bound together)

12. 2. Each tyrosine binds a phosphate from an ATP (requires 6 ATP molecules)

13. 3. Binding of phosphates activates receptor proteins and initiates a cellular response for each of the tyrosines
One ligand results in multiple cellular responses

15. Ligand-gated ion channels
Specific ligand can cause ion channels in membrane to open or close
Allows for facilitated diffusion to occur
Change in ion concentration results in a change in cell activity

16. Transduction Relays signal from receptor to target
Often involves several steps

17. Phosphorylation Cascade
Phosphorylation cascade – allows for amplification of the signal (1 ligand can result in the response happening many times
Each step in the signal-transduction pathway involves enzymes call protein kinases
One protein kinase phosphorylates the next, causing a chain reaction in which thousands of protein kinases are activated

19. Protein phosphatases
Protein phosphatases – enzymes that remove phosphate groups
Inactivates protein kinases and therefore turns off the signal

20. Secondary Messengers Non-protein, water-soluble molecules or ions
Once activated, can initiate a phosphorylation cascade
Examples – calcium ions in muscle contractions or cyclic AMP which activates protein kinases

21. Response
In the nucleus, response is a regulation of protein synthesis by turning genes on/off
For example, the final activated molecule can be a transcription factor (proteins that regulate transcription – making mRNA from DNA to use for protein synthesis)

22. In the cytoplasm, regulate protein function
Regulate enzyme activity by having the final activated molecule be a coenzyme or an inhibitor
Opening/closing of ion channels

23. Apoptosis (Programed Cell Death)
Cell suicide – the cell is dismantled and digested
Protects neighboring cells – otherwise dying cell could release digestive enzymes
Essential for vertebrate development, nervous system function, immune system function, and morphogenesis
***Molecules/components are recycled***