1. Chapter 11 Notes
Cell Communication

2. Cellular Internet
Cell to Cell communication essential for multicellular organisms
Coordinates activities of cell
Help fertilized egg to become entire organism

3. External Signals Bacteria Yeast Use signals for survival
Aggregate (group) with other bacteria to survive harsh conditions
Make walled fruiting body when food is scarce
Yeast
Send signal to other yeast cell for mating
Use Signal Transduction Pathway

4. Local Signaling For cells in Direct or Close contact
Through Cell Junctions
Gap junctions – animal cells
Plasmodesmata – plant cells
Cell-Cell Recognition
Molecules on cell surface interact together

5. Local Signaling Paracrine Signaling Synaptic Signaling
Local regulators travel short distances
Growth Factor stimulate growth and division in neighbor cells
Synaptic Signaling
Neurotransmitters released at the end of a nerve cell to a target cell
Stimulates response in target

6. Long Distance Signaling
Hormones travel long distances to target cells
In animals – travel through blood stream
In plants – travel through air (gas) or through plant vessels

7. Stages of Cell Signaling
Reception
Signaling molecule binds to a protein on cell membrane
Transduction
Several steps using a Signal Transduction pathway to cause changes in next molecule
Response
A specific response is triggered in a cell

9. Reception
Receptor Proteins on or in target cell allow a response to a signal
Very specific
Signaling molecule works like a Ligand
Causes change in receptor protein

10. Membrane Receptors G Protein-Coupled Receptor
Works with a G protein using GTP (like ATP but with guanine instead of adenine)
Causes 1 response only

11. Membrane Receptors Receptor Tyrosine Kinases Have Enzyme Activity
Kinase catalyzes transfer of phosphate groups
Cause MANY responses

12. Membrane Receptors Ion Channel Receptors
Region that acts as a gate when receptor changes shape
When gate opens – ions move

13. Intracellular Receptors
Found in cytoplasm or nucleus of target cells
Must pass through plasma membrane
Hydrophobic or small molecules
Ex – Steroid Hormones like testosterone move into cell, bind to receptor in cytoplasm and move to nucleus to turn on a gene
Ex – Thyroid hormone enters cell and finds receptor in nucleus

15. Transduction Usually multiple steps involved
Many activate proteins by adding phosphates
Signal can be amplified for a bigger reaction
Opportunities for coordination and regulation of cellular activities
Works using Signal Transduction Pathway
Often makes a Phosphorylation Cascade

16. Transduction Protein Kinase Protein phosphatase
Enzyme that phosphorylates a protein (adds a Pi)
Changes shape of protein to activate it
Protein phosphatase
Removes a phosphate from a protein (dephosphorylate)
Inactivates a protein

18. Transduction – 2nd Messengers
Small molecules and ions
Can spread rapidly through cell by diffusion

19. 2nd Messenger Cyclic AMP cAMP is made from ATP by an enzyme
cAMP activates Protein Kinase A to initiate a response in the cell
Does NOT use phosphorylation cascade

21. cAMP - examples
Ex – Cholera – bacteria keeps GTP stuck onto a G Protein – makes cAMP and causes constant release of salt in intestines – draw in water – give you diarrhea
Ex – Viagra
cGMP is second messenger - relaxes smooth muscles by keeping cycle on
Dilates blood vessels all over body

22. 2nd Messengers
Calcium
Concentration in cytosol lower than outside cell (10000x less)
Reception signal hits cell
Activates enzyme
Makes IP3 (2nd messenger)
IP3 connects to protein in ER
Gate opens
Ca2+ is released
Activates a protein to make a response
Ex – muscle contraction, nervous signals

24. Response
Signal transduction pathway leads to regulation of one or more cellular activities
Can act as a transcription factor to turn a gene on or off
Might regulate the activity of a protein
Open/close channel
Cause change in cell metabolism
Cause change in cell shape – growth of microfilaments/microtubules

25. Response

26. Response Amplification
Once an enzyme is activated, it can make lots of products
The more steps involved in a pathway, the more the signal can be amplified
Small amount of signal can lead to lots of response

27. Response Specificity of Cell Signaling
Different cells have different collections of proteins
The response of a cell to a signal depends on the type of receptor proteins, relay proteins, and response proteins

29. Response Scaffolding Proteins
Help to hold a pathway together to make it faster and more efficient

30. Response Termination of the Signal
Binding of original signal is reversible
Less signal molecule = less response

31. Apoptosis Programmed Cell Death Chop DNA and fragment organelles
Cell shrinks
Parts are packaged in vesicles and digested by scavenger cells
Protects neighboring cells from damage

32. Apoptosis Signal received
Starts a pathway that turns on a C death gene (Ced)
Activates a protease (eats proteins) or a nuclease (eats nucleic acids)
Signal might come from
Another cell
Nucleus if there are problems with DNA
ER if there is a protein folding problem