It's a G-protein cascade, so you have a Rhodopsin. Okay, you have a Rhodopsin, and then you have the G-protein, and is this. G-protein, and then the downstream factor is a force for or PDE. [FOREIGN] When you have this [INAUDIBLE] p concentration drops what will happen? This channel will close. A channel closed in the cell is hyperpolarization. [FOREIGN]. In the visual system, the light stimulation caused the cell hyperpolarization. [FOREIGN]. In most other sensory system you have stimulus to cell is excitation. They depolarize. [FOREIGN]. Okay, so. [FOREIGN]. Let's take a look actually about this arrange happen on this membrane. You have a photon come in, and then you activate this guy, you see, this one. Go to a straight form, right? [FOREIGN] G-protein binding site [FOREIGN]. Sub unit beta gamma [FOREIGN] Separate. Of course you need a, this guy [FOREIGN] ADP [FOREIGN]. Activated protein, G-protein then will make the separation, alpha, beta, gamma. In this case, alpha is the active form. [FOREIGN]. As a case, there can be the beta gamma is the active form, okay? [FOREIGN]. Gamma is the inhibitor sub unit. So the G-protein then release the gamma inhibition, okay? [FOREIGN]. Okay. [FOREIGN] [FOREIGN]. In the dark, high level of the right? Right now you have a light activation, then it drops. [FOREIGN] [FOREIGN] Now I will explain later in the next lecture. Okay, so this is the important, this part. So this is the process of the phototransduction. The light or the photo absorption traduce into electric signal. And then this process actually is quite complicated. So why you need such a complicated process here? [FOREIGN] biochemical reaction cascade. [FOREIGN] >> [INAUDIBLE] >> Amplification, okay, good. Okay, the advantage is you gain the amplification. [FOREIGN]. We need a single photon detection. [FOREIGN]. Okay, that's good. Amplification [FOREIGN] amplification [FOREIGN]. 1,000 cGMP molecules. So in total, then you have 20,000 amplification here, right? So you can detect a single photon. Yeah, of course here is the advantage. You have the huge amplification. What is the disadvantage? >> [INAUDIBLE] resolution. >> You have that temporary resolution. >> Yeah. >> Good. Now so this system, you have a huge amplification but the problem is actually, because this is a bio-chemical reaction. [FOREIGN] Each step you need the time. You build up these molecules which takes time. So the temporary resolution is not good. Okay, here. [FOREIGN]. Okay so that's it for this lecture. Any questions? If no questions that's fine.