Phototransduction: How we see photons

Vision begins when a light-detecting molecule absorbs a photon, and our eyes are sensitive enough to allow us to detect changes to individual molecules in a cell. This requires amplification of a tiny signal to produce an electrical response large enough for our brain to notice through a process called phototransduction.

In this video, I show how this amplification is a physical process, relying on random motion and chance encounters, but that produces repeatable and reliable signals.

0:00 Introduction
1:05 Photoreceptors
1:36 Rhodopsin
2:04 Amplification
3:16 Cyclic GMP
4:01 Electric signal
6:16 Recovery
6:48 Conclusion

Animations were made in Blender and Maya by Kerry Kim. This video is copyright (c) 2021 by Kerry Kim. All rights reserved. No part of this video may be used without my prior written permission, except as permitted by U.S. copyright law.

3D coordinate files for proteins:

PDB ID: 7LFY
Xue, J. Han, Y., Zeng, W., Wang, Y., Jiang, Y. (2021) Structural mechanisms of gating and selectivity of human rod CNGA1 channel. doi: 10.2210/pdb7LFY/pdb

PDB ID: 7JSN
Gao, Y., Eskici, G., Ramachandran, S., Skiniotis, G., Cerione, R.A. (2020) Structure of the visual signaling complex between transducin and phosphodiesterase 6. doi: 10.2210/pdb7JSN/pdb

PDB ID: 1GOT
Lambright, D. G., Sondek, J., Bohm, A., Skiba, N.P., Hamm, H.E., Sigler, P.B. (1996) Heterotrimeic complex of a gt-alpha/gi-alpha chimera and the gt-beta-gamma subunits. doi: 10.2210/pdb1GOT/pdb

PDB ID: 1F88
Palczewski, K., Kumasaka, T., Hori, T., Behnke, C.A., Motoshima, H., Fox, B.A., Le Trong, I., Teller, D.C., Okata, T., Stenkamp, R.E., Yamamoto, M., Miyano, M. (2000) Crystal structure of bovine rhodopsin. doi: 10.2210/pdb1F88/pdb

[KerryKim]

NOTE: Low bandwidth video compression struggles with large numbers of randomly-moving particles such as confetti or the diffusing ions and molecules shown in this video. If the video looks muddy or you can't see what's happening, you may need to switch to watching the HD version of the video: click the gear icon next to the video then 'quality' and select the 1080p or HD version. Also, watching on a computer with a large screen and good internet connection will help. The most affected parts are from 4:00-4:30 and 5:12-6:00 in this video. My apologies for the compression artifacts, but fortunately Youtube allows you to select higher quality versions if your device and internet connection allow.

[PinataOblongata]

As someone who did a whole degree in molecular biology, I can't stress enough how well-made this video is, specifically in relation to the "quantitative thinking" concept and visualising/explaining the real physical interactions that take place, instead of just explaining a singular, neat cascade like most university lectures do. The "random motion" part of such processes is almost never elucidated and students come away thinking things are a lot more static and straight-forward than they are. Translation is a classic example, where the mechanism is described something like, "the ribosome incorporates the next amino acid in the chain, " rather than letting students know that the correct amino acid actually has to randomly bump into the complex for that to happen - it sounds counter-intuitive unless you have a good grasp on how fast molecules are bumping around and interacting per second.

[starwarized]

the complexity of organic life is mindblowing. All this is happening in one single cell, of one single part of a body full of millions of cells with different functions, every single milisecond. And it all evolved from a single first cell just by random iteration. it feels like it simply shouldn't be possible, but here we are. it's amazing.

[redox]

This channel is gonna be another classic in the scientific YouTube side.

[labibbidabibbadum]

I honestly don't know what to be more astounded about:
1. That this occurs
2. That we could possibly understand it
3. That you're able to describe it so beautifully.

The amplification of the energy of a few photons into our visual sense of a scene taking place in the world is so incredible. I had heard that our ears can distinguish vibrations in air the size of half a hydrogen atom (which I hope you will do a video on). That amplification is also mindblowing, but I hadn't considered it for light before.

[Catpain_Tailspin]

Amazing animations and descriptions, perfect unison of media for explaining molecular biology.

[joe-uqqi]

I had no idea that the process of vision was so complex and interesting. What fascinates me the most about all this is that while I am watching your video, what you are explaining to me is happening in myself.

[HasBeensNAddicts]

This is a very stupid comment but it amazes me that any of this exists. Even the fact we were able to figure this out. Blows my mind

[friedpicklezzz]

It’s insane how complex and beautifully orchestrated this all is. And it’s equally impressive that science has figured out these processes.

[TheStringKing]

Absolutely amazing animations and easy to follow explanations. I have always assumed that the many biological processes look exactly like this but seeing it so clearly is so beautiful. I would love more videos just like this one, related to biophysics. For example how do other homeostatic processes in the body look and function on this small scale. Keep up the good content.

[bushwalker]

Great video! And this complexity and beauty appeared absolutely randomly just within 1 billion years. Yeah, right.

[samuelsanchezmaza]

WHERE ARE YOU??? Those astonishing animations should not end, please do more, biomedical students need you 😭

[codydicken]

My god this was one of the best videos I’ve ever seen

[heidideplazes]

I literally watched 5 videos and reread my book like 3 times to try to understand this concept and all the videos were either lacking labels or lacking visuals. This one actually made it slightly understandable. Thank you. Difficult concept to explain and show, but you did a great job.

[AquaSearanium]

absolutely loved this eloquent teaching of yours, kerry. im excited to see and learn more from you!

[avantgaarden]

I wish you had hundreds of these videos. Thank you

[TheBillNye]

Please keep making videos. Your animations are some of the best I’ve ever seen and you do a fantastic job explaining the concepts. I work as a biology tutor and I will 100% be sharing this video!

[joe-uqqi]

Intuitively, I have always thought that the vision process was instantaneous. but after seeing your explanation I realize that it takes a certain time from when the light hits us until it reaches our brain, imperceptibly, very little time, but something. my mind lives nanoseconds in the past. Amazing. thanks for the video

[WolfgangFeist]

Thanks - really great. The more we understand these processes, the more we realize, what a great accomplishment sentimental life really is.

And, in the same time, how evolution left its trace in each of these (quite complicated) processes. This is all not necessarily an absolute optimum - but a lot of local ones, improved step by step, very old "solutions" left in place, even if these sometimes seem a little bit odd (like the place of the light sensitive membranes on the back side of the retina).

[mastershooter]

People say there is beauty in simplicity, I would say there's also just as much beauty in complexity and this whole process has an awe-insipiring amount of complexity and it's just a simplification!! And of course this was an amazingly well put together video! Beautiful visuals and crystal clear explanations! Great job!!