Back To CourseFundamental Biology
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Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.
Effective communication has two major components: the sender and the receiver. The sender of a message must be clear about what they are saying, and the receiver must not only be able to receive that message but also clearly understand it.
Communication between cells works the same way. Cells 'talk' to each other through signaling molecules called ligands. These are molecules that bind to other specific molecules, similar to how a key only fits into a specific lock. The molecules that ligands bind to are called receptor proteins because they receive the signal sent to them. This first step in cellular communication is called reception because this is the stage where the target cell receives the signaling molecule.
But what happens after the message is received? Just like your friend's brain has to 'decode' your words in a conversation, the ligand's signal must be 'decoded' so it can be understood by the cell. In cellular communication, this step is called transduction. It's a series of events that converts the signal so the target cell can respond.
The final step of cellular communication is response, which is when the target cell responds to the signal it received. This is just like your communication partner responding to your words by smiling, crying, or getting angry, depending on what you said to him or her.
In other lessons, we go into detail about reception and response. So in this lesson, we'll focus on transduction, the second step in the cellular communication process.
Transduction often occurs in multiple steps, called the signal transduction pathway. The message itself gets relayed down the line, like a baton in a relay race being passed from one person to the next.
This multi-step approach can be beneficial to the cell for a few reasons. One way this may help the cell is that the signal itself can be amplified to numerous molecules at each individual step. This works similarly to how a chain letter spreads. You start by sending the letter to five people, who each send it on to five more people. In just two steps, your letter has now reached 30 people, whereas if it was only sent to one person at a time, you would have reached only two. By amplifying the signal like this, there will be more activated molecules at the end of the pathway in the cell.
The multi-step process of transduction also serves to fine-tune the signal as it moves along. This is like the chain of command in an office. One person may write an office memo, but before it goes out to all employees, it's reviewed by a supervisor. It may then be further reviewed by that person's supervisor, and so on up the line. This controls the final message that is sent out, refining it as it moves along the pathway.
Proteins are often activated when a phosphate group is added to it, a process known as phosphorylation. This occurs through protein kinases, which are enzymes that transfer phosphate groups to a protein. These helpers are often found along the signal transduction pathway and may act on other protein kinases, triggering a phosphorylation cascade. Just like falling dominoes, each phosphorylation triggers another as each protein along the pathway becomes activated.
Protein phosphatases are also important players along the phosphorylation cascade. These are enzymes that quickly remove phosphate groups from proteins. If this sounds like the reverse of phosphorylation, you're right! This process of removing phosphate groups is called dephosphorylation. After the protein sends the signal on to the next protein in line, its services are no longer needed so it's important to turn it 'off' again. For example, cells that go unchecked may grow abnormally, which is one way that cancers develop in the body.
While kinases are indeed very important, other non-protein molecules serve important roles in transduction as well. Second messengers are small, water-soluble molecules that relay signals. Why second? Because the ligand is considered the 'first messenger' as it is the first molecule to deliver the signal to the cell, which occurs earlier during reception.
Once a signal has been received at the receptor protein during reception, the signal must now be relayed like a baton through the cell. This second stage of cell signaling, called transduction, actually consists of multiple steps along the signal transduction pathway.
Signals don't just magically travel down the pathway, though. One of the most important components of transduction is an enzyme called protein kinase, which adds a phosphate group to a protein, a process known as phosphorylation. When a protein kinase triggers the phosphorylation of other protein kinases, we get a phosphorylation cascade. Similar to a row of falling dominoes, each protein kinase is acted on by the one before it, relaying the signal along the pathway.
Conversely, protein phosphatases are enzymes that remove phosphate groups from proteins, a process known as dephosphorylation. This is what turns the protein kinase off, making it available for use at a later time.
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Back To CourseFundamental Biology
36 chapters | 334 lessons