Transduction: Phosphorylation Cascades


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My AP Biology Thoughts

Unit 4 Cell Communication and Cell Cycle

Welcome to My AP Biology Thoughts podcast, my name is Corrinna and I am your host for episode #88. This is Unit 4 Cell Communication and Cell Cycle and today, we will be talking about transduction phosphorylation cascades

Segment 1: Introduction to transduction: phosphorylation cascades

  • Transduction is the second step in cell signaling pathways. It comes after reception, where the signal (which is called the ligand) is received by the receptor.
  • In order for the signal to start a response in the protein, the receptor needs to be activated. For the cell to produce a response, the next proteins in the chain also need to be activated. These proteins can be activated and deactivated like an on/off switch.
  • One of the ways that the signaling molecules are activated is phosphorylation. For a molecule to be phosphorylated, phosphate is added to the molecule. Phosphate groups are typically linked to either tyrosine, threonine, or serine, since these amino acids have hydroxyl groups in their side chains.
  • Phosphorylation is what can activate or deactivate the signaling molecules. It can also make the proteins more active (like an enzyme) or cause it to be broken down. Additionally, phosphorylation generally isn’t permanent. To de-phosphorylate a protein, cells have enzymes called phosphatases that remove the phosphate groups from the phosphorylated protein.
  • A phosphorylation cascade is when multiple signaling molecules in the cell signaling chain are phosphorylated, which transports the signal to another molecule to produce the end result.

Segment 2: examples of transduction: phosphorylation cascades

  • In order to better understand phosphorylation cascades, let’s look at an example.
  • One example of a phosphorylation cascade is the epidermal growth factor (EGF) pathway.
  • When growth factor ligands bind to the receptors, the receptors act as kinases and attach phosphate groups to each other’s intracellular tails. These receptors are now activated, triggering a series of events. Since these events don’t include phosphorylation, we won’t cover them in detail and will instead talk about the parts after that series that do involve phosphorylation.
  • Those events activate kinase Raf. This activated Raf phosphorylates and activates MEK, which in turn phosphorylates and activates ERKs. The ERKs then phosphorylate and activate other target molecules that then promote cell growth and division.
  • This specific pathway is called a mitogen-activated protein kinase cascade.
  • Because this specific pathway used multiple phosphorylation events that triggered other phosphorylations, it can be classified as a phosphorylation cascade.

Segment 3: Connection to the Course

  • Phosphorylation cascades are extremely important in cell signaling pathways because they allow the cell to respond to more than one cell signal. Phosphorylation cascades trigger multiple cellular responses, because the phosphorylation of one protein leads to the phosphorylation of another.
  • Additionally, if phosphorylation cascades become out of control, especially cascades that signal for growth factor, cancer can occur. This shows that being able to stop cell signaling is extremely important, since if cell growth and division goes unregulated, it becomes dangerous.
  • To stop cell growth and division, the cell may receive a signal to undergo apoptosis, or cell death. This usually happens if a cell doesn’t pass a checkpoint in the cell cycle, which is explained in further detail in another episode.

Thank you for listening to this episode of My AP Biology Thoughts. For more student-run podcasts and digital content, make sure that you visit See you next time on My AP Biology thoughts Podcast!

Music Credits:

  • "Ice Flow" Kevin MacLeod (
  • Licensed under Creative Commons: By Attribution 4.0 License

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