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PROFESSOR: Any questions about where we left off-- up to where we left off? OK, what I'll do then is give you a few more examples of the combinations in 22 to show which ones we have to retain as frameworks for crystallographic point groups and which ones exist as groups but which involve rotational symmetries that are not permitted to a lattice. So we've seen a combination of three orthogonal twofold axes and then projection that would look like this. And the international symbol for that point group is just a running list of the different axes that are present, 222. The next group in the sequence would be 3 2 2, where we took a 120 degree rotation. We combine that with a twofold axis perpendicular to it and the new twofold axis comes out and reminds you again of things that are quite clear but which are easy to forget-- that this angle here is 1/2 of 2 pi over 3. Don't forget that 1/2. So the neighboring twofold axis is 60 degrees away and then if we allow t...

PROFESSOR: Any questions before I obliterate all this lovely geometry? No. OK. We handled them during intermission I guess. Let me do a couple more plane groups just very quickly to show you how they come out without going through all of the steps, because I think we've seen now what one has to do to derive these. There are two that are left. One is a threefold axis, and if that's all the symmetry we've put into the lattice, we're combining a threefold rotation axis with a primitive lattice, and we know that this has to be hexagonal net. Because from our depth of experience, we know that is the shape of a lattice that is demanded by a threefold axis. It has two translations, T1, that are identical in length. And this angle between them is exactly 120 degrees. That's what we saw a threefold access require. So now what we are doing is putting in a threefold axis at one lattice point, and this means we are adding the operations A 2 pi over 3. A minus 2 pi...

There were some other questions sort of running along this general idea of the fact that the information in DNA doesn't go, even though it encodes the information for proteins goes via this rRNA intermediate. Someone asked what was the M. The M is for messenger. The idea being that since the DNA, at least in eukaryotes the DNA was in the nucleus and proteins were made out of the cytoplasm, somehow that information had to be carried from the nucleus where the DNA was out to the cytoplasm. And that's where the term messenger was because the RNA was seen as something that would carry the information out. Now, a point here, it's really critical because we're going to continue to talk about gene regulation. And that is when a cell is making one of these mRNAs, it doesn't make one single copy of all of the genes that are in the genome on one RNA. Instead it does it either one gene at a time, which is the usual case, or occasionally as we see in the lac opero...

PROFESSOR 1: Yeah, any questions about this? Yeah. AUDIENCE: I actually have two. One's an incidental question. You keep mentioning something that I never heard of called "ardeeno", or something like that. PROFESSOR 1: Yes. AUDIENCE: What is that? PROFESSOR 1: Arduino is a tiny little microcontroller-- not related to video games, really. But it's a tiny little microcontroller. And you connect it up to a circuit, and then it can tell an LED to blink every five seconds. And it can detect when you press a button, and it can read off of a light sensor, whether the lights are on. So it's a little kind of computer chip that you program to do one particular task that connects out to the world. AUDIENCE: So then the more generally-- I'm curious what the connection with Kinect is in this course. If we didn't want to use Kinect, is that an option? The reason I'm a little nervous is because I don't own one, and I don't have access to one. So...