1. How Do We Communicate? Pass notes Email Tweet
Have to be near someone and directly hand it to them.
Talks to one specific person (or selected people) but you can talk from anywhere.
Tweet
Sending a message out to everyone, and the readers can respond as they choose

2. Cells Communicate in Similar Ways.

3. Short Distances Vs. Long Distances
Sometimes cells want to communicate with cells near by.
If they are touching they can use gap junctions or plasmodesmata to communicate.
If they are not touching, they have to use a local regulator, such as the neurotransmitter.
Some cells are communicating with cells far away.
They usually involve hormones from your endocrine system to complete this task.

4. Specific Vs. Not Specific Messages
Sometimes cells will send a signal through the body for more than one cell to act on, so cells will receive the signal and “decide” if they need to act.
Other times signals are very specific and one cell can send a signal to one specific type of cell.

5. Cell Signaling
No matter how they receive a signal, they all go through three processes
Reception
Transduction
Response

7. Reception
A signal molecule called a ligand binds to a receptor protein.
Highly specific like a lock and key
Receptor protein changes shape starting the transduction of the signal.
Most signal receptors are plasma membrane proteins.
G protein coupled receptors
Receptor tyrosine kinases
Ion channel receptors

8. Transduction Use of Signal Transduction Pathways
Usually involves multiple steps.
Provides more opportunities for coordination and regulation of the cellular response.
Amplifies the response: a few molecules can produce a very large response.

9. Response The transduction pathways trigger a response.
The response can occur in the cytoplasm or the nucleus.
Can be anything such as:
Change in cytoskeleton
Activation of a gene
Activation of an enzyme

10. Termination of the Signal
After the signal is given, it must be terminated.
Unbound receptors will revert to an inactive state once ligand concentration is low.

11. Apoptosis
Apoptosis, or programmed cell suicide is an important example.
Triggered by extracellular death-signaling ligand, DNA damage in the nucleus, or protein misfolding in the ER.