I've been watching some videos on signal transduction and it says that because there are enzymes being activated by the signal, then there is a "cascade" which happens afterwards...I don't understand why?


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    $\begingroup$ Is your question "Why a long cascade instead of more simple, shorter cascade?" $\endgroup$ – Remi.b Apr 3 '15 at 18:34

There is one main reason: Amplification of the signal. You can start a signal downwards the cascade with relatively few receptors which need to be activated which allows even for weak signals to be translated into the nucleus.

This figure shows this for G protein coupled receptors (from here):

enter image description here

For example one molecule of cAMP can activate many molecules of pKA until it's hydrolysed which in turn can phosphorylate many other protein molecules.

For more information you can read the references articles (at least the introduction) and follow the references in them.


  1. Ultrasensitivity in the mitogen-activated protein kinase cascade
  2. Noisy signal amplification in ultrasensitive signal transduction
  • $\begingroup$ Ok I think I get it now. It starts with ONE ligand, the epinepherine. However it says that after the ligand binds and thus activates the G protein, it has 100 molecules activated? I thought that 1 ligand activates 1 G protein? I think I'm a bit unsure on what exactly the G protein is and what the G protein RECEPTOR is? $\endgroup$ – Paze Apr 3 '15 at 18:38
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    $\begingroup$ No, 1 ligand activates one receptor. The receptor in turn binds inactive G-proteins and activates these (as long it is active himself). The activated G proteins are released from the receptor and activate downstream targets of the cascade. This is the first step of amplification. $\endgroup$ – Chris Apr 3 '15 at 18:40
  • $\begingroup$ So the G proteins are not on the membrane already? Does the ligand bind the receptor, which in turn recruits G proteins in the cytosol up to the membrane or? The information is very blurry on this. It seems to assume the G proteins and the receptor as one unit. $\endgroup$ – Paze Apr 3 '15 at 19:04
  • $\begingroup$ It will be pretty hard to explain this in detail here in the comments (and is not well liked as well). I suggest you open a new question on this with detailed things you want to know about it. $\endgroup$ – Chris Apr 3 '15 at 20:17
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    $\begingroup$ @jerepierre There are more potential points to terminate a signal. But it also allows crosstalk between different pathways and more noise. See here for some more information. $\endgroup$ – Chris Apr 3 '15 at 20:43

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