After reception of a signaling molecule and movement of that signal through transduction, the cell can now respond. There are different types of cellular response as well as different mechanisms the cell uses to make this process more efficient.
The Signal Transduction Pathway
During a war, orders within an army follow a certain chain of command.
A general may send out orders for a mission, but it is likely that this mission is written in secret code to prevent spies from understanding the message. Once that message is received by the correct person, it is then decoded so that all of the troops can understand the mission and carry out the actions specified.Communication among your cells follows a similar pattern, called a signal transduction pathway. There are three main steps in this pathway: signal reception, which is when the target cell receives a signaling molecule; transduction, which is a series of events that converts the signal to something the target cell can respond to; and cellular response, which is when the target cell responds to the signal.
Within your body, the message or signal is sent out by a signaling cell and received by a target cell, decoded within the target cell, and then a response occurs within that cell based on the signal it received.We learned about signal reception and transduction in detail in other lessons, so this lesson will focus specifically on the final step of cell signaling – cellular response.
The End of the Line
Cellular response is the end of the line for a signal brought to the target cell by a signaling molecule.
Once the signal has gone through transduction in the target cell, it is is now ready to be put into action as a cellular response. There are so many different types of responses that we just can’t list them all here. But some of the major ones include regulation of protein synthesis and activity as well as cell division, shape, and growth.Protein synthesis is just a fancy way of saying ‘making proteins.’ Proteins do all sorts of things, like receive signaling molecules, assist with DNA replication, or help break down food into smaller particles so that you can utilize its nutritious goodies.
In addition to making proteins, regulating when they are ‘on’ or ‘off’ is also important. Some proteins regulate ion channels in a cell’s plasma membrane. You don’t want this on or off all the time because your cells need to maintain a certain ionic balance.
Turning this protein ‘on’ at only the appropriate times helps maintain that balance.Regulating cell division and growth is an important response because uncontrolled cell reproduction and growth are major contributors to the development of cancer.Cellular response may occur in either the cell’s nucleus or in the cytoplasm, but regardless of where it occurs, the response needs a bit of tweaking before it’s ready for action.
Amplifying the Signal
One way that a cell can make the most of a signal it receives is to amplify that signal along the transduction pathway.
This is similar to sending out a chain letter that requires each person to forward it to multiple people. Instead of passing along through individual receivers in a linear fashion, the letter gets ‘amplified’ as it is sent to more and more people each time it’s passed along.Cells can do something similar with signals. This benefits the cell because it means that the cell can increase the number of responses for that signal in fewer steps, making the process more efficient.For example, say our army general sent his orders to one person, but that person then sent it on to five people, and each of those five people passed the orders on to five more people, and so on.
Soon, you get a pyramid of communication, where more and more people receive the order but in less time than communicating with each individual. So more troops get the orders and can respond more quickly.
Coordinating the Response
Different kinds of cells may have different responses to the same signal. The response of a certain type of cell depends on the proteins that receive the cell, decode it, and respond to it. This is a very good thing because you certainly wouldn’t want your liver responding the same way to signals as your heart or your brain. Each of these cells is specific, and this is an important differentiation.
But we can also have different responses to a signal within the same cell. For example, a cell may have two different transduction pathways so that depending on which pathway is triggered, the cell responds differently. Some cells also respond the same way to different signals so that the same pathway is triggered for a certain response but from many different types of signaling molecules.
Why is this beneficial to the cell? Let’s look at our army communication again. The general may send out his order and expect it to reach several different sets of troops. But if the order is for troops to attack a central area, and each set of troops is attacking from a slightly different location, following the exact same orders would not be very productive. Instead, the main order is passed along the line of communication, but as it branches out to different locations, the orders are adjusted so that they are appropriate to each unique set of troops.
Yet another way that cellular response is made more efficient is with scaffold proteins. These are large proteins that are attached to other proteins involved in transduction. Proteins that are involved in transduction are not all connected in a line, just waiting for a signal to turn them on. They are floating around in the cytoplasm of a cell, but because they are fairly large, they don’t move around very quickly.
What a scaffold protein does is move many proteins at once, much like large ship carries many soldiers to shore at the same time. If each of the people on the ship were to travel by canoe to reach that same destination, it would be a much less efficient process because each of those people would be taking up space on the water and along the shore with their canoes. Additionally, each canoe would require a lot of paddling effort, taking more time to travel than the ship would to move the same number of people the same distance. Can you see how moving many proteins at once would be more efficient for cellular response?
Terminating the Signal
Finally, turning the response off is just as important as turning it on. A signaling molecule binds to a receptor protein during signal reception, but this is a reversible process. Once a signaling molecule leaves the receptor protein, that protein is inactivated or turned ‘off.’ This triggers the line of molecules that are involved in signal transduction to turn ‘off’ as well, ending the entire signal transduction pathway process and freeing the cell to respond to a new signal that may come its way.
Cellular response, or a cell’s response to a signal, is the final step in the signal transduction pathway. Cellular response may be amplified during the transduction process, which increases the efficiency of the response because more responses can be triggered in a shorter amount of time. Signals can also be coordinated so that they respond appropriately. Different types of cells may respond differently to the same signal, but a single cell may also have different ways it can respond to a signal.
Cellular response may also be made more efficient with the use of scaffold proteins, which move multiple proteins through the cytoplasm at once. Once cellular response is complete, it’s important for the cell to turn off the signal transduction pathway. The signaling molecule leaves the receptor protein, switching all of the proteins down the line to the ‘off’ position. This then frees the cell to receive and respond to a new signal, which starts the process all over again.