Hi, welcome to the wrap-up for lecture three. We're sitting this time, Till and I, together with Neda who you've met before, Neda Ghotbi who is a doctoral student with us and Manfred Gödel, who is a PhD student with us, and one of your teacher assistants. Charissa de Bekker, a post doc from the lab and David Lenssen also a Phd student who is again one of the teacher assistants. So molecular mechanism lecture, any pressing questions? >> Yes, I actually have one. So I am wondering, why is it that every cell has its own clock? That's a good question. Actually I thought about a cell. You have unicellular organisms, multicellular organisms, but let's say a cell. A cell is also an an organism, which contains elements of circadian system like an input, an oscillator and an output. They might use this just as well in order to adapt and anticipate its environment. >> There even are some selfish gene theories out there that talk about cells within organisms of, as being their own sort of evolutionary units. So maybe the clock is even evolving in cells in organisms? Other questions? [SOUND]. >> So has this, the molecular mechanisms of the transcription translation feedback loops in between the animals and plants and fungi are also similar? But the clock genes which are used the sequence of them is so different? >> Well, actually this is, this is quite common. You see this across many different mechanism, biological mechanisms that are very important for organisms to survive. So for instance for the immune system if you look across kingdoms for instance plants and animals, they might use different proteins to - for instance detect - if if there's a pathogen that is trying to invade. But the mechanisms are very, very similar. And vice versa, all these parasites, they use very similar mechanisms as well. So yeah, you see this across different, different mechanisms. It's still not just the clock genes actually. >> Clock genes, clock control genes. How does one distinguish between clock and clock control genes? Well, if you knock out a gene within the rhythm generator, you have to really look at all potential rhythms that they are gone. So, as a concept it's very easy. A clock controll gene will not knock out other clock controll genes whereas a clock gene in them also able to knock out all of them. Experimentally it's very difficult to show all this. >> Mm-hm. >> Yeah, that sort of actually backs the question. It brings up another point that people often ask. So how do you define a clock gene or what, what is a clock gene? And I guess the most conservative and traditional definition has been something that changes the free-running period. And so, initially there were just a few and we find more and more genes that seem to change the free-running period under some conditions. And that's how we end up with this very complex molecular network. I still think this is incredibly conservative as a method because the free running period is one of several key clock properties. And as we keep emphasizing and saying possibly and likely a more important clock property is what's the clock doing under entrainment. And if we would screen under entrainment, as a couple of our colleagues have started to do now, I guess that we would find even more and more components that are really affecting a key circadian phenotype. And I would campaign that these should also be called clock genes and then we would end up with a very huge molecular network. But I think we'd closer to a fuller understanding of how the clock is working. >> So if there are more questions you could ask these questions in the discussion forum. In this lecture we heard a lot about molecular mechanisms of the core clock gene processes. In the next lecture you will hear something about clock controlled mechanisms. So how the clock regulates metabolism and the behaviour. [SOUND].