Microbes and Photosynthesis Insights

Okay, welcome back. Hopefully you had a nice restful spring break and off we go. There's only four weeks left in this semester so keep that in mind. Don't let it sneak up on you. Right? Attendance. I calculated attendance for everyone and then posted the grade. There will be two grades. grades you see. One is top head attendance. Ignore that one. Well, not ignore it, but it doesn't count towards your grade. That just tells you how many times the system has recorded you being here. The other grade is active load. learning points I think I called it. And that is the get grade to pay attention to. You get 30 points if you're doing fine. If you're not, it'll be below that and you know. I had a student come up and talk to me this morning that said, hey, I've been here every day, but why do I have a zero? Please get in contact with me over Piazza or class or whatever if the system's having issues. Right, so I know, so that we can work it out. All right, the exam. Exam three will be online. You get one shot at it, right? It will be available from April 9th to April 12th. You can take it any time during that time, right? So any time during those three days, you can take that exam. It's up to you when you do it. That will be on regulation and then microbes in the environment. And speaking of microbes in the environment, let's begin. Last week, we ended talking about the different phylotypes in the ocean. The one thing I want you to get from this is that, first of all, we've sampled all the world's oceans now, and there's actually a consortia, the Terra Oceans Foundation, that can accumulate... this data and we have data from all over the world, but one of the interesting things you see is it's not the same everywhere. The ocean is different depending upon the weather, land masses, et cetera, so that's not surprising since it's different parts of the ocean. However, if you take the data from the Saucer 2 and you look at it and you take those sequences and you take all the different reads that they had, they had tens of thousands of reads, right, almost over. a million reads. What's a read? That is just a block of sequence that they then assembled. Right? And if you look at them and you can classify these into different organisms, you find again this pattern that I've talked about. There will be a few dominant genera and then you'll have this long tail of everything else. And you'll see that the oceans... In general, and again, this is a massive generalization, and as I showed you, this changes. But in general, the ocean is dominated by five different species, or genre. Polygobacter, Prochlorococcus, Synchrococcus, Burkholderia, and Shiwanella. For this class, we are going to focus on the top three and look at what actually they do. Now... For lakes, we talked about a proteobacteria called AC1 and said that that was 50% of the lakes. It turns out polygabacter, which they used to call SAR11 but has now been isolated, it was isolated, its first isolation was in nature in 2002, and it now is a species. It's called polygabacter ubique because it is ubiquitous. In the oceans, it can make up to 30, 40% or more of the biomass, the microbial biomass in an area, or the microbial numbers in an area. It is oligotroph. What that means is it grows in low nutrient density. It only grows in low nutrient density. It grows very slowly. takes 23 days for it to grow from a low populations to a higher population. And that is at 15 degrees centigrade. So it likes it colder, that's its optimum. It will only grow in seawater medium. What is seawater medium? Seawater medium is they take seawater and they autoclave it, and they use that as their base for the medium. They don't just use tap. If they use tap water, it won't grow. However, we've been able to, in the recent years, replicate a seawater medium that's incredibly complex. It has all sorts of ions and different things in it that will support the growth of lots of these organisms. It is a chemo-heterotroph. It will grow on organic compounds, just a variety of organic compounds, amino acids, sugars, things like that. And it's reasonably metabolically capable. It can synthesize most of the amino acids and vitamins and everything it needs. It doesn't have a lot of growth factors. Here's a little image of it and this bead is one micron. Actually no, that bead is two microns. Let me double check that. Yeah, that bead is about two, is actually one micron. This is a one micron bead and you can see that these are quite small, right? E. coli will normally be about the width of this bead. So these cells are smaller than E. coli. Now, interestingly, this organism contains proteorhodopsin. And they think that just like the actinorhodopsin that we talked about before, this is another way of it for generating energy. It can create a proton gradient and generate excess ATP from sunlight. Again, it's not photosynthesis, but it can do that. So that's polygabacter. The other two that we're going to talk about are pleurochlorococcus and synchrococcus. These are cyanobacteria. They're photosynthetic bacteria. They are present in the open oceans. And they take light and they grow on that. And they use the two species generally we're going to talk about, a prochlorococcus. These are very small, 0.6 micron cyanobacteria. Again, here is an image of prochlorococcus growing in culture. And those are very small, 0.6 microns. Again, 0.6 millionths of a meter. They inhabit subtropical and tropical oceans, so 45 degrees north, which is about the latitude of Wisconsin, right, the center of Wisconsin, about 45 degrees north, all the way down to 40 degrees south, so they don't go above that or below that. They can grow at very low light and at deep depths, right? The other cyanobacteria... is synchrococcus. This is found in all oceans. This organism is quite larger. Here's, you know, that bar is 20 microns. So this is probably three or four microns for each cell. And then it looks to be about a width of about two microns. So these are quite a bit larger. They are phylogenetically diverse. There are organisms, synchrococcus species in the genre. They can grow in freshwater. and there are organisms that can grow in salt water. We're talking about the salt water cyanobacteria. They are obligate photoautotrophs, right? And they're about 0 to 1.6 micron ovoid cells, although honestly, on this micrograph, they look quite a bit bigger. I'm just giving you quite a quick estimate there. All right, so to summarize, the open oceans is dominated by just... five genre and the ones that we talked about were three different genre. Polygabacter, Prochlorococcus, and Synchrococcus. And Prochlorococcus and Synchrococcus are cyanobacteria. Now all of these use light as part of their metabolism, at least somewhat, and Prochlorococcus and Synchrococcus are cyanobacteria. So this is a good time to have a big segue into photosynthesis. All right, so photosynthesis, the general scheme is you use light to create both a proton gradient across the membrane and generate reducing power. The two things that you need out of catabolism, right? And the general scheme is this. You will have light harvesting complexes shown here. These contain photopigments. These photopigments absorb photons in light and they focus it on a reaction center. That reaction center takes that light and takes a low-energy electron that it gets from somewhere and these will normally be low energy or electrons from like hydrogen or water or hydrogen sulfide. It takes those low energy electrons and boosts their energy. and then passes it off to a cunon. So it gives it, makes it a high-energy electron, it then goes on to a cunon, and then it goes through electron transport chain, which pumps protons across the membrane, and that electron can either come back to the reaction center to power another cycle through to pump more protons, or it can be dumped onto NADP to make NADPH, which is reducing power. Now I'm giving you a quick summary of that. We're going to go into the details in just a second. In fact, let's do that now. Let's talk about the different pieces. So the first thing is the light harvesting complexes. These are collectors that supply photons. They're made of protein and pigments. And these pigments will be either chlorophyll or bacterioclorophyll. And you can see that here. Here's a photopigment here, right? Here's a light harvesting protein in red, and then here's some photopigments bound to this, and those photopigments are pointed in such a direction that they can collect light, right? So here's the outer membrane at the top, at the bottom here we have the, you know, inner membrane. So these are in the membrane. They'll also have bacteriophyll phyton, which is a chlorophyll-like molecule without the magnesium, or they'll also have carotenoids. These are highly ordered structures, right? Those pigments are held in a specific position. It's not like wiggling around and floating around in there. It's a very ordered structure that holds the pigments in precise positions. And why does it do that? To collect light. Here is an example of a light harvesting complex in the purple bacteria. You have all these light harvesting complexes out here. This goes to, this is a peripheral center. Then you have the core center and then you have the reaction center, right? So the peripheral, the core, and then the reaction center. And all the light collected by these guys, all these photons, are focused on the reaction center. And so that's what I want you to remember. The light harvesting complex's purpose is to collect light and focus it on the reaction center. Alright, so here is actually the structure of chlorophyll. You can see the bacterial chlorophyll has a very similar structure to chlorophyll It's just a few of the different carbons are arranged a little differently on it. Same thing It's this ring like structure with a magnesium ion in the center or magnesium in the center, right? Okay, so if you look at chlorophyll that's used in plants and cyanobacteria Here's its absorption spectrum. If you look at bacteria chlorophyll, it has a different absorption spectrum and they kind of absorb at different wavelengths to take advantage of different wavelengths in the environment and to not compete with each other. So cyanobacteria, right, don't compete with the purple bacteria, which absorb a different wavelength of light. So the chlorophyll's This gives you an example of the structure. All these double bonds are really good at absorbing light, right? And then that can get transferred. So that's what the chlorophylls are doing. They're helping absorb light. Carotenoids. Carotenoids, and here's one example of a carotenoid. It's dihydroneurosporine, and it has this long structure. and it has alternating double bonds in it. I don't expect you to recognize or be able to draw that structure at all. I want you to know what a carotenoid is, and I want you to know the purpose. Common structure is this long alkyl chain with many double bonds in it, right? It can have zero, one, or two cyclic rings at the end, right? What these guys do, carotenoids aren't really that important in absorbing light. They can do some of that, but what they're really important for is protecting from reactive byproducts. They are widely distributed and they may be a little important in light harvesting. But what they're really important for is protection. So when light is hitting chlorophyll molecules and light harvesting complexes in the reaction center, it will excite electrons, right? And that electron is excited out of the magnesium. What the hope is is that then that goes on to a bacterial pheophyton. and then that goes on to a quinone, and then out through the electron transport chain. Sometimes side reactions happen, especially if oxygen is present, and the electron is donated to form singlet oxygen. You first form this triplet state of chlorophyll, which is bad, right? You get this electron hopped up into a high orbital, and then that can react with oxygen and form this singlet oxygen. The quinone... ... is there to quench this triplet state of chlorophyll. So if the magnesium electron hops up to this triplet state, the chlorophyll is there to grab that electron and calm it down. And what it does is it goes back and forth in that carotenoid and all those double bonds in that big orbital that forms. And it slows it down, it runs out of energy, and then it gets handed back to the magnesium line. So are you guys familiar with antioxidants? It's a big thing. You need to eat antioxidants and protect yourself from reactive oxygen species. That's what a lot of these antioxidants are. They're plant-based chemicals such as carotenoids, which carrots have a lot of. beta-carotene that actually have this protective role and can deal with reactive oxygen species. It's the same thing that's happening in these reaction centers. So the chlorophyll is actually ideally positioned to do this. This is the reaction center from rotavacrys spheroides. I have shown you two chlorophyll molecules and how they're positioned. This is what's called the special pair. This is where all the photons are focused, right, to make that excited electron. And right here in orange is the carotenoid. It's perfectly positioned to be able to intercept any kind of side reactions that you don't want, such as this triplet state of bacterial chlorophyll. Okay, there's lots of different photopigments that are involved. Here are example of a whole bunch of carotenes, right, that are involved in photo protection, right. They're photo protection and they absorb at different wavelengths. Again, this is for illustration only. It's giving you examples of different carotenoids. And you can see, right, here's some with no rings on either side. Here's some with two. Here's one. Here's beta carotene. Here's alpha carotene with just one, etc. What I want you to remember about carotenoids are that they're very important in protecting the complex from the triplet state of oxygen or other reactive oxygen species. Okay, so I've told you that pigments in photosynthesis... are very carefully held and they're held in specific positions. I've told you that the carotenoid is arranged in a certain place, I've told you the special pair is in a certain place. Why? Light harvesting pigments are near the outside of the cell. Pigments in the reaction center are positioned to allow efficient transfer of light energy and the rapid transfer of that energy into an energized electron. Light energy travels a downhill path to the reaction center. What does that mean? A downhill path is the... The parts of the reaction center that are farther away, or the light harvesting complexes that are farther away, have a shorter wavelength and higher energy, and they can transfer that energy to those closer in that can absorb longer wavelengths, which are lower energy. Okay, so if we go back to this figure, right? This outside light harvesting complex, this absorbs energy, this is again the purple bacteria, at about 807 nanometers. The inside light harvesting, light harvesting one absorbs energy at 850 nanometers and then that gets donated to the reaction center. You can see those here, 805 and 870. So right there. Okay, so the reaction center. This is where the light energy is focused. Again, here's the reaction center from rhodobacter sororities, and this is a purple non-sulfur bacteria. We'll talk about that. The pigments, they have a special pair. That's the bacterial chlorophyll that create the excited electron from magnesium that goes through the electron transport chain. They have carotenoids for protection. They have bacteriophyton and namhin iron and quinones. And again, these last three are involved in the electron transport chain. Okay, so what happens? Okay, so you have this magnesium ion at energy state zero. It gets hit by energy, and then it gets excited. to a higher energy state. Then that electron goes through the electron transport chain. So the light energy of the photons is what drives the electron to a higher energy state, to a higher electron potential. In the purple bacteria, and the reaction center is at 870, It actually raises it from electron volts of about 500 millielectron volts to minus 1,000 millielectron volts. So it gives it very high energy, then it hits bacterioclorophyll, then it hits bacteriophyll phyton, then it goes through some quinones, and then it goes through the cytochrome bc1 complex. And that's diagrammed over here. Here is the electron here in the chlorophyll, right? It goes through bacterioclorophyll right here. Then it goes to bacteriophyll phyton. Then, you know, then it goes into quinone A and then quinone B. The quinone comes out. And now this is the same thing that we just discussed in respiration, the cytochrome BC1 complex. The quinone comes out. The electrons are donated, but some of them end up, because of the spatial arrangement, going outside the cell, and the protons, right, they get picked up, they go outside the cell, and then the electrons end up on a cytochrome, and then cytochrome C2, and that donates them back. So what I want you to remember from this diagram is that light actually brings that electron's energy up from a pretty low level, 0.5 electron volts, up to minus one, and then it goes through a series of electron carriers, and it ends up donating through the cytochrome BC1 complex, which ends up pumping protons across the membrane. Now, we talked about this mechanism before when we talked about respiration. it's the same mechanism. Right? So light is used to raise the energy electrons. That high energy electron goes through electron transport chain and ends up pumping protons across the membrane. And it actually ends up using proteins that you're familiar with already. Okay, and this is just another summary of the same process. Now, you can actually look at this. This is a crystal structure of this. This is the reaction center. Here's the bacterial chlorophyll here, right? Then it goes into a bacterial pheophyton. It goes into a non-heme iron right there, and then it goes onto the quinone, and this quinone in blue ends up going out into the cytoplasm. So they've actually figured out this in great detail. Alright, so the essential parts of any photosynthetic organism are a light harvesting complex, a source of electrons, you gotta get your electrons from somewhere, a reaction center where the light is focused, an electron transport chain that creates a proton gradient, And that proton gradient is then used to make ATP through ATP synthase. Finally, you need an exit path for the electrons that results in the synthesis of NADPH, right? Reduced NAD. Alright, so those are the essential parts of photosynthesis. Okay, after that long summary, let's see how you're doing. Okay, what I want you to do is arrange the following proteins in the purple bacteria electron transport chain. The numbers in parentheses are the electron potential in milli-electron volts of each complex. And you can talk to your neighbors to figure this out. Thank you. Okay, 10 seconds. All right, here are the responses. And the most common response was just to order them by number, right? The highest energy is the excited electron in the bacterial chlorophyll. And as you can see, you go down the thing. The one error here is this should not be there. It should be at the bottom. So the correct answer is here, right? It goes back to your pheophyton, then quinoa A, then quinoa B, then cytochrome BC1, then cytochrome C2, and it ends up as the unexcited electron on the bottom. So good. Most people got the right answer there. Okay, I want to ask... Okay, we'll keep going then. Alright. Alright, so from there we have now several types. We've given you the general scheme of how photosynthesis works. I'm going to introduce you very briefly to the three different types of bacteria that you can find and they can do photosynthesis and they can be broken into two groups. Anoxygenic, that means it does not generate oxygen. Okay, don't confuse that. with like aerobic or anaerobic, right? Anoxygenic means that it does not generate oxygen. Oxygenic means it generates oxygen. Those are the two types, anoxygenic and oxygenic. Anoxygenic, again, does not generate oxygen. They use many different things for sources of electrons, things like hydrogen sulfide. Organic acids such as malic acid, succinic acid, oxalic acid, right? Hydrogen they can use as sources of electrons. These will be things like the purple bacteria, the green bacteria, and the heliobacteria, right? Oxygenic, during the process of photosynthesis, they generate oxygen. This is plant-like photosynthesis. They will use water as their source of electrons and the group that we'll talk about here is the cyanobacteria. Alright, so some general information about each group. The purple bacteria, these are found in freshwater and marine environments. If you go into Lake Mendota in the summer, And if you take a plastic tube, almost like a big straw, and you drive it down about 10 meters and pull it up, about 3 meters down, you'll find a line of purple sulfur bacteria growing. So they're always in Lake Mendota. So are the cyanobacteria. You see those because the whole thing turns green. So the water does. They're gram-negative rods or spirilla. Here's some examples of different organisms. This is rhodomicrobium vanellii. You don't need to know these. I think this is rhodosudomonas. And this is, let's see if I got it written down. I do, yes. Rhodomicrobium vanellii is on the left, rhodosudomonas is in the middle, and rhodosudomonas, these are both rhodosudomonas, so I was right, different species. These are all members of the alpha, beta, or gamma proteobacteria. So really interestingly, The proteobacteria is this really large group of genetically similar organisms by 16S ribosomal RNA, but the capability to photosynthesize is kind of distributed throughout the group in certain genre. There's not like a special isolated group. They do their photosynthesis, the electron donors will be hydrogen sulfide. Hydrogen or organic acids such as malic acid or succinate, right? They will oxidize sulfur to sulfate and they'll obtain their carbon from CO2 organic acids or carbon monoxide. One of my friends in graduate school was doing research on rhodobacter soroides and he was, or rhodosporin rubrum actually. You don't need to remember that. But he was trying to demonstrate. Their ability to grow in the presence of carbon monoxide, so he had to grow these huge vats of these bacteria. It was this giant fermenter that was, you know, eight feet, you know, eight, seven, eight meters tall, right? And they had a light in the center of it, and they had to feed carbon monoxide in it. But they had to be very careful not to feed too much carbon monoxide, so it bubbled out. And one time in the lab... Everybody started feeling nauseous and it's like they had turned the carbon oxide up too high. So fortunately I wasn't in the lab that day. So here's what you it's very easy to isolate these guys. You can take water from Lake Mendota and you just put it in a medium that has succinate in it and make it anaerobic. Succinate cannot be fermented. And then you expose it to light. The only thing that will be able to grow that... Are these bacteria? And you can get all different species, and these are just some examples of vials I pulled after letting these incubate for about two weeks in the presence of light. One thing that's really interesting about the purple bacteria is they can grow under, they are not limited to photoautotrophy. They can grow photoautolithotrophically on CO2, hydrogen sulfide, and light under anaerobic conditions. But they can also grow with carbon monoxide as their carbon source. They can grow photo-hetero-organotrophically. Using succinate as their carbon source and their source of electrons, but using light as their energy source But you can also just grow them in plain old media You can streak these out on media and grow them in the dark and they'll do grow just fine As long as you provide a carbon source and they can grow on all sorts of that things in fact, the purple bacteria are pretty versatile they can grow on sugars and Alkanes and all sorts of crazy stuff that you can give them that makes them great model systems for doing research in this area. Okay, so they're light-hypersensing complexes. Their photosystem is housed in an intercytoplasmic membrane, an ICM. So this is a transmission electron micrograph and they've taken the cell and like sliced it down the middle. And you can see that their membranes, there's little tubes that are pushed into the cytoplasm. to expand the membrane so that you can put more of these light harvesting complexes into the membrane. You have peripheral light harvesting complexes, you have core light harvesting complexes, and they surround the reaction center as we showed in the diagram earlier. Right, so we talked about how light goes around and around, it goes through the cytochrome BC1 complex. pumps protons across the membrane. The one thing that we didn't talk about is how do they get reduced electrons, right? So the energy source, these do not have a high enough electron potential to actually, after they get to the quinone, donate the electrons to NAD to P to make NADPH. Okay, so that if you under standard conditions, Quinones will not donate electrons to NADP. So what does these organisms do when they need reducing power? They do something pretty amazing. They take advantage of Le Chartier's principle. They shut down the cyclic electron transport, so they stop pumping protons. So then reduced quinones build up to very high level, and it shifts the equilibrium. So now it can donate electrons to NADPH, or NADP. So I thought that was worth mentioning. Not going to test you on that, but I think it's a really interesting thing that they can regulate where the electrons go and shut off electron transport when they need more NADP, or the proton pumping when they need more NADP. Okay. The other group is the green bacteria. The green bacteria, unlike the purple bacteria, are obligate phototrophs. They only grow photoautotrophically, right? They harvest light via the chloroform. And unlike, again, the purple bacteria that are scattered throughout the proteobacteria, the green bacteria will cluster into a distinct group. And they are not closely related to other phototrophs. If you take their 16S ribosomal RNAs, you sequence them and you line them up in a tree of life, they will all cluster together in one group. I've given a bunch of examples of the different organisms, and you know they're kind of neat to look at. Some of them will actually accumulate sulfur globules. Outside the cell, some will accumulate sulfur globules inside the cell, but I don't expect you to remember any of these names. I am going to focus a little bit on the chlorobaceae, which are green sulfur bacteria, and talk about their physiology as an example. Okay, these are strict anaerobes. They can only grow under anaerobic conditions. They are obligate photoautolithotrophs, and their electron donor... All can use hydrogen sulfide. Some can use hydrogen gas or thiol sulfate as their source of electrons. But in the environment, they're probably using a lot of hydrogen and hydrogen sulfide. All right, the reason I'm focusing on them is they have a very interesting light harvesting complex. It's called a chlorosome. Now, this diagram is a little bit upside down, right? The outside is here. The inside is here. So this is under the membrane. Light hits this, and it's absorbed, and it's focused then on the reaction center right down here, right? It's just under the cytoplastic membrane. And the bacterial chlorophyll C that's in here is not in a protein. This is a lipid membrane, right? It's encased in a lipid coating. And this is a crystalline array. And this array is very sensitive and very good at collecting photons. So it's a very efficient light collector. And because of that, these green bacteria can grow in places that are very dim. There isn't a lot of light, but they can still get enough to grow. So chlorosomes do not have proteins in this structure right here in the chlorosome, but they have like a crystalline array of chlorophyll. Okay, if you look at them, here is the chlorosome next to the reaction center. You have this core polypeptide. You have a light harvesting protein, you have a C-type cytochrome, and then you have, again, a BC1 complex. So what happens is the electrons go through these chlorophylls, they dump onto a quinone again, the quinone goes out to the BC1 complex, and you get this cyclic electron transport that pumps protons across the membrane. Now... The way they have things arranged, the electron actually is of high enough energy by the time it gets down to NAD that it can make NADH without any kind of special exceptions. Okay, so that's that. Finally, we have the cyanobacteria. And this is from a Nature article that was discussing the cyanobacteria at Yellowstone. Here's the hot... spring at Yellowstone, and you can see the water here is greater than 95 degrees, and see that it's blue, there's no life. But as soon as it starts to cool down, it's about 75 degrees centigrade, you get these bacterial mass, and they're growing at 75 degrees centigrade, and then they get pretty abundant even at 65 degrees centigrade. And that green and red, that is cyanobacteria. So that's pretty amazing. These are ubiquitous in the environment. You will find them in deserts, in tropical rainforests, oceans, and even thermal hot springs. They are gram-negative, they are obligate phototrophs, and they do oxygenic photosynthesis. This is plant-like photosynthesis, as we talked about, and they form a very tight phylogenetic group, right? They cluster all together in a phylogenetic tree. Their light harvesting complex is a little different, but it's the same idea. You have the photosynthetic machinery in thylakoid membranes, and you have phycobilly proteins, and you have different ones. Phycorethrin, outside, phycocyanin, next, and alpha-cyanin, allophycocyanin, I should say, right next to the reaction center. And as you can see, you're starting with shorter wavelengths, higher energy, and it's transferring down through. and then focused on the reaction center. Why have these different wavelengths? So you can collect more different wavelengths of light. When you have these three different proteins here, you can collect everything from 550 to 650 nanometers. And it all gets focused on the reaction center. And again, the arrangement of the proteins with the higher energy light collectors on the outside, and the lower energy on the inside allows efficient energy transfer to the reaction center. Okay, here's the reaction center. This is a, interestingly, if you sequence the proteins in the green reaction center and you compare them to photosystem 1 in cyanobacteria, there is a significant amount of homology. If you sequence the purple reaction center and you compare that to photosystem 2 In cyanobacteria, there is again a significant amount of homology. There are different numbers of proteins in chemistry, but there's homology there, and it suggests the hypothesis that the cyanobacteria arose when these two complexes transferred into one microorganism. Okay, for this one... I have a little animation. Okay, here's all the different complexes. All right, here we go. Here's photosystem II. Electrons go in here. They go to plastocyanin, or they go to this the cytochrome BC1 complex like, goes to plastocyanin, goes through, and then this goes through. This is non-cyclic photosynthesis here, right, going from here, photosystem II to photosystem I. This is cyclic photosynthesis here. Right? In both cases, protons get pumped across the membrane. Okay, that is... Photosynthesis. What I want you to do, and this will be the last exercise we do today, is I want you to compare retinal based phototrophy to photosynthesis. What are their similarities and what are their differences? So write down as many ideas as you can come up with. Thank you. Okay, we got about a minute left, so here I'll give you the answers that I came up with. Right? Similarities, they both use a proton gradient. They generate ATP versus ATP synthase. They have photopigments and a membrane is required. Differences, photosynthesis has a reaction center. Photosynthesis has light-harving complexes. Retinal has a retinal-based phototrophy, right? RBT is one protein. The photo can generate and reduce NAD to NADPH. The photo can fix carbon dioxide. All right. See you Wednesday.

Okay, welcome back. Hopefully you had a nice restful spring break and off we go. There's only four weeks left in this semester so keep that in mind. Don't let it sneak up on you. Right?

Attendance. I calculated attendance for everyone and then posted the grade. There will be two grades.

grades you see. One is top head attendance. Ignore that one. Well, not ignore it, but it doesn't count towards your grade.

That just tells you how many times the system has recorded you being here. The other grade is active load. learning points I think I called it.

And that is the get grade to pay attention to. You get 30 points if you're doing fine. If you're not, it'll be below that and you know. I had a student come up and talk to me this morning that said, hey, I've been here every day, but why do I have a zero?

Please get in contact with me over Piazza or class or whatever if the system's having issues. Right, so I know, so that we can work it out. All right, the exam. Exam three will be online. You get one shot at it, right?

It will be available from April 9th to April 12th. You can take it any time during that time, right? So any time during those three days, you can take that exam.

It's up to you when you do it. That will be on regulation and then microbes in the environment. And speaking of microbes in the environment, let's begin. Last week, we ended talking about the different phylotypes in the ocean. The one thing I want you to get from this is that, first of all, we've sampled all the world's oceans now, and there's actually a consortia, the Terra Oceans Foundation, that can accumulate...

this data and we have data from all over the world, but one of the interesting things you see is it's not the same everywhere. The ocean is different depending upon the weather, land masses, et cetera, so that's not surprising since it's different parts of the ocean. However, if you take the data from the Saucer 2 and you look at it and you take those sequences and you take all the different reads that they had, they had tens of thousands of reads, right, almost over.

a million reads. What's a read? That is just a block of sequence that they then assembled. Right? And if you look at them and you can classify these into different organisms, you find again this pattern that I've talked about.

There will be a few dominant genera and then you'll have this long tail of everything else. And you'll see that the oceans... In general, and again, this is a massive generalization, and as I showed you, this changes. But in general, the ocean is dominated by five different species, or genre.

Polygobacter, Prochlorococcus, Synchrococcus, Burkholderia, and Shiwanella. For this class, we are going to focus on the top three and look at what actually they do. Now...

For lakes, we talked about a proteobacteria called AC1 and said that that was 50% of the lakes. It turns out polygabacter, which they used to call SAR11 but has now been isolated, it was isolated, its first isolation was in nature in 2002, and it now is a species. It's called polygabacter ubique because it is ubiquitous.

In the oceans, it can make up to 30, 40% or more of the biomass, the microbial biomass in an area, or the microbial numbers in an area. It is oligotroph. What that means is it grows in low nutrient density. It only grows in low nutrient density.

It grows very slowly. takes 23 days for it to grow from a low populations to a higher population. And that is at 15 degrees centigrade. So it likes it colder, that's its optimum.

It will only grow in seawater medium. What is seawater medium? Seawater medium is they take seawater and they autoclave it, and they use that as their base for the medium.

They don't just use tap. If they use tap water, it won't grow. However, we've been able to, in the recent years, replicate a seawater medium that's incredibly complex. It has all sorts of ions and different things in it that will support the growth of lots of these organisms.

It is a chemo-heterotroph. It will grow on organic compounds, just a variety of organic compounds, amino acids, sugars, things like that. And it's reasonably metabolically capable. It can synthesize most of the amino acids and vitamins and everything it needs. It doesn't have a lot of growth factors.

Here's a little image of it and this bead is one micron. Actually no, that bead is two microns. Let me double check that. Yeah, that bead is about two, is actually one micron. This is a one micron bead and you can see that these are quite small, right?

E. coli will normally be about the width of this bead. So these cells are smaller than E. coli. Now, interestingly, this organism contains proteorhodopsin.

And they think that just like the actinorhodopsin that we talked about before, this is another way of it for generating energy. It can create a proton gradient and generate excess ATP from sunlight. Again, it's not photosynthesis, but it can do that. So that's polygabacter.

The other two that we're going to talk about are pleurochlorococcus and synchrococcus. These are cyanobacteria. They're photosynthetic bacteria. They are present in the open oceans. And they take light and they grow on that.

And they use the two species generally we're going to talk about, a prochlorococcus. These are very small, 0.6 micron cyanobacteria. Again, here is an image of prochlorococcus growing in culture.

And those are very small, 0.6 microns. Again, 0.6 millionths of a meter. They inhabit subtropical and tropical oceans, so 45 degrees north, which is about the latitude of Wisconsin, right, the center of Wisconsin, about 45 degrees north, all the way down to 40 degrees south, so they don't go above that or below that. They can grow at very low light and at deep depths, right?

The other cyanobacteria... is synchrococcus. This is found in all oceans.

This organism is quite larger. Here's, you know, that bar is 20 microns. So this is probably three or four microns for each cell. And then it looks to be about a width of about two microns.

So these are quite a bit larger. They are phylogenetically diverse. There are organisms, synchrococcus species in the genre.

They can grow in freshwater. and there are organisms that can grow in salt water. We're talking about the salt water cyanobacteria.

They are obligate photoautotrophs, right? And they're about 0 to 1.6 micron ovoid cells, although honestly, on this micrograph, they look quite a bit bigger. I'm just giving you quite a quick estimate there. All right, so to summarize, the open oceans is dominated by just...

five genre and the ones that we talked about were three different genre. Polygabacter, Prochlorococcus, and Synchrococcus. And Prochlorococcus and Synchrococcus are cyanobacteria. Now all of these use light as part of their metabolism, at least somewhat, and Prochlorococcus and Synchrococcus are cyanobacteria. So this is a good time to have a big segue into photosynthesis.

All right, so photosynthesis, the general scheme is you use light to create both a proton gradient across the membrane and generate reducing power. The two things that you need out of catabolism, right? And the general scheme is this.

You will have light harvesting complexes shown here. These contain photopigments. These photopigments absorb photons in light and they focus it on a reaction center. That reaction center takes that light and takes a low-energy electron that it gets from somewhere and these will normally be low energy or electrons from like hydrogen or water or hydrogen sulfide. It takes those low energy electrons and boosts their energy.

and then passes it off to a cunon. So it gives it, makes it a high-energy electron, it then goes on to a cunon, and then it goes through electron transport chain, which pumps protons across the membrane, and that electron can either come back to the reaction center to power another cycle through to pump more protons, or it can be dumped onto NADP to make NADPH, which is reducing power. Now I'm giving you a quick summary of that. We're going to go into the details in just a second. In fact, let's do that now.

Let's talk about the different pieces. So the first thing is the light harvesting complexes. These are collectors that supply photons. They're made of protein and pigments. And these pigments will be either chlorophyll or bacterioclorophyll.

And you can see that here. Here's a photopigment here, right? Here's a light harvesting protein in red, and then here's some photopigments bound to this, and those photopigments are pointed in such a direction that they can collect light, right?

So here's the outer membrane at the top, at the bottom here we have the, you know, inner membrane. So these are in the membrane. They'll also have bacteriophyll phyton, which is a chlorophyll-like molecule without the magnesium, or they'll also have carotenoids. These are highly ordered structures, right? Those pigments are held in a specific position.

It's not like wiggling around and floating around in there. It's a very ordered structure that holds the pigments in precise positions. And why does it do that? To collect light.

Here is an example of a light harvesting complex in the purple bacteria. You have all these light harvesting complexes out here. This goes to, this is a peripheral center.

Then you have the core center and then you have the reaction center, right? So the peripheral, the core, and then the reaction center. And all the light collected by these guys, all these photons, are focused on the reaction center.

And so that's what I want you to remember. The light harvesting complex's purpose is to collect light and focus it on the reaction center. Alright, so here is actually the structure of chlorophyll.

You can see the bacterial chlorophyll has a very similar structure to chlorophyll It's just a few of the different carbons are arranged a little differently on it. Same thing It's this ring like structure with a magnesium ion in the center or magnesium in the center, right? Okay, so if you look at chlorophyll that's used in plants and cyanobacteria Here's its absorption spectrum. If you look at bacteria chlorophyll, it has a different absorption spectrum and they kind of absorb at different wavelengths to take advantage of different wavelengths in the environment and to not compete with each other.

So cyanobacteria, right, don't compete with the purple bacteria, which absorb a different wavelength of light. So the chlorophyll's This gives you an example of the structure. All these double bonds are really good at absorbing light, right?

And then that can get transferred. So that's what the chlorophylls are doing. They're helping absorb light.

Carotenoids. Carotenoids, and here's one example of a carotenoid. It's dihydroneurosporine, and it has this long structure. and it has alternating double bonds in it. I don't expect you to recognize or be able to draw that structure at all.

I want you to know what a carotenoid is, and I want you to know the purpose. Common structure is this long alkyl chain with many double bonds in it, right? It can have zero, one, or two cyclic rings at the end, right?

What these guys do, carotenoids aren't really that important in absorbing light. They can do some of that, but what they're really important for is protecting from reactive byproducts. They are widely distributed and they may be a little important in light harvesting.

But what they're really important for is protection. So when light is hitting chlorophyll molecules and light harvesting complexes in the reaction center, it will excite electrons, right? And that electron is excited out of the magnesium. What the hope is is that then that goes on to a bacterial pheophyton. and then that goes on to a quinone, and then out through the electron transport chain.

Sometimes side reactions happen, especially if oxygen is present, and the electron is donated to form singlet oxygen. You first form this triplet state of chlorophyll, which is bad, right? You get this electron hopped up into a high orbital, and then that can react with oxygen and form this singlet oxygen.

The quinone... ... is there to quench this triplet state of chlorophyll.

So if the magnesium electron hops up to this triplet state, the chlorophyll is there to grab that electron and calm it down. And what it does is it goes back and forth in that carotenoid and all those double bonds in that big orbital that forms. And it slows it down, it runs out of energy, and then it gets handed back to the magnesium line. So are you guys familiar with antioxidants?

It's a big thing. You need to eat antioxidants and protect yourself from reactive oxygen species. That's what a lot of these antioxidants are.

They're plant-based chemicals such as carotenoids, which carrots have a lot of. beta-carotene that actually have this protective role and can deal with reactive oxygen species. It's the same thing that's happening in these reaction centers.

So the chlorophyll is actually ideally positioned to do this. This is the reaction center from rotavacrys spheroides. I have shown you two chlorophyll molecules and how they're positioned.

This is what's called the special pair. This is where all the photons are focused, right, to make that excited electron. And right here in orange is the carotenoid. It's perfectly positioned to be able to intercept any kind of side reactions that you don't want, such as this triplet state of bacterial chlorophyll.

Okay, there's lots of different photopigments that are involved. Here are example of a whole bunch of carotenes, right, that are involved in photo protection, right. They're photo protection and they absorb at different wavelengths.

Again, this is for illustration only. It's giving you examples of different carotenoids. And you can see, right, here's some with no rings on either side. Here's some with two.

Here's one. Here's beta carotene. Here's alpha carotene with just one, etc. What I want you to remember about carotenoids are that they're very important in protecting the complex from the triplet state of oxygen or other reactive oxygen species.

Okay, so I've told you that pigments in photosynthesis... are very carefully held and they're held in specific positions. I've told you that the carotenoid is arranged in a certain place, I've told you the special pair is in a certain place.

Why? Light harvesting pigments are near the outside of the cell. Pigments in the reaction center are positioned to allow efficient transfer of light energy and the rapid transfer of that energy into an energized electron. Light energy travels a downhill path to the reaction center.

What does that mean? A downhill path is the... The parts of the reaction center that are farther away, or the light harvesting complexes that are farther away, have a shorter wavelength and higher energy, and they can transfer that energy to those closer in that can absorb longer wavelengths, which are lower energy. Okay, so if we go back to this figure, right? This outside light harvesting complex, this absorbs energy, this is again the purple bacteria, at about 807 nanometers.

The inside light harvesting, light harvesting one absorbs energy at 850 nanometers and then that gets donated to the reaction center. You can see those here, 805 and 870. So right there. Okay, so the reaction center. This is where the light energy is focused. Again, here's the reaction center from rhodobacter sororities, and this is a purple non-sulfur bacteria.

We'll talk about that. The pigments, they have a special pair. That's the bacterial chlorophyll that create the excited electron from magnesium that goes through the electron transport chain.

They have carotenoids for protection. They have bacteriophyton and namhin iron and quinones. And again, these last three are involved in the electron transport chain.

Okay, so what happens? Okay, so you have this magnesium ion at energy state zero. It gets hit by energy, and then it gets excited. to a higher energy state. Then that electron goes through the electron transport chain.

So the light energy of the photons is what drives the electron to a higher energy state, to a higher electron potential. In the purple bacteria, and the reaction center is at 870, It actually raises it from electron volts of about 500 millielectron volts to minus 1,000 millielectron volts. So it gives it very high energy, then it hits bacterioclorophyll, then it hits bacteriophyll phyton, then it goes through some quinones, and then it goes through the cytochrome bc1 complex. And that's diagrammed over here.

Here is the electron here in the chlorophyll, right? It goes through bacterioclorophyll right here. Then it goes to bacteriophyll phyton.

Then, you know, then it goes into quinone A and then quinone B. The quinone comes out. And now this is the same thing that we just discussed in respiration, the cytochrome BC1 complex. The quinone comes out.

The electrons are donated, but some of them end up, because of the spatial arrangement, going outside the cell, and the protons, right, they get picked up, they go outside the cell, and then the electrons end up on a cytochrome, and then cytochrome C2, and that donates them back. So what I want you to remember from this diagram is that light actually brings that electron's energy up from a pretty low level, 0.5 electron volts, up to minus one, and then it goes through a series of electron carriers, and it ends up donating through the cytochrome BC1 complex, which ends up pumping protons across the membrane. Now, we talked about this mechanism before when we talked about respiration. it's the same mechanism.

Right? So light is used to raise the energy electrons. That high energy electron goes through electron transport chain and ends up pumping protons across the membrane. And it actually ends up using proteins that you're familiar with already. Okay, and this is just another summary of the same process.

Now, you can actually look at this. This is a crystal structure of this. This is the reaction center. Here's the bacterial chlorophyll here, right? Then it goes into a bacterial pheophyton.

It goes into a non-heme iron right there, and then it goes onto the quinone, and this quinone in blue ends up going out into the cytoplasm. So they've actually figured out this in great detail. Alright, so the essential parts of any photosynthetic organism are a light harvesting complex, a source of electrons, you gotta get your electrons from somewhere, a reaction center where the light is focused, an electron transport chain that creates a proton gradient, And that proton gradient is then used to make ATP through ATP synthase.

Finally, you need an exit path for the electrons that results in the synthesis of NADPH, right? Reduced NAD. Alright, so those are the essential parts of photosynthesis.

Okay, after that long summary, let's see how you're doing. Okay, what I want you to do is arrange the following proteins in the purple bacteria electron transport chain. The numbers in parentheses are the electron potential in milli-electron volts of each complex. And you can talk to your neighbors to figure this out.

Thank you. Okay, 10 seconds. All right, here are the responses. And the most common response was just to order them by number, right? The highest energy is the excited electron in the bacterial chlorophyll.

And as you can see, you go down the thing. The one error here is this should not be there. It should be at the bottom.

So the correct answer is here, right? It goes back to your pheophyton, then quinoa A, then quinoa B, then cytochrome BC1, then cytochrome C2, and it ends up as the unexcited electron on the bottom. So good.

Most people got the right answer there. Okay, I want to ask... Okay, we'll keep going then. Alright. Alright, so from there we have now several types.

We've given you the general scheme of how photosynthesis works. I'm going to introduce you very briefly to the three different types of bacteria that you can find and they can do photosynthesis and they can be broken into two groups. Anoxygenic, that means it does not generate oxygen.

Okay, don't confuse that. with like aerobic or anaerobic, right? Anoxygenic means that it does not generate oxygen. Oxygenic means it generates oxygen. Those are the two types, anoxygenic and oxygenic.

Anoxygenic, again, does not generate oxygen. They use many different things for sources of electrons, things like hydrogen sulfide. Organic acids such as malic acid, succinic acid, oxalic acid, right?

Hydrogen they can use as sources of electrons. These will be things like the purple bacteria, the green bacteria, and the heliobacteria, right? Oxygenic, during the process of photosynthesis, they generate oxygen.

This is plant-like photosynthesis. They will use water as their source of electrons and the group that we'll talk about here is the cyanobacteria. Alright, so some general information about each group. The purple bacteria, these are found in freshwater and marine environments. If you go into Lake Mendota in the summer, And if you take a plastic tube, almost like a big straw, and you drive it down about 10 meters and pull it up, about 3 meters down, you'll find a line of purple sulfur bacteria growing.

So they're always in Lake Mendota. So are the cyanobacteria. You see those because the whole thing turns green.

So the water does. They're gram-negative rods or spirilla. Here's some examples of different organisms. This is rhodomicrobium vanellii. You don't need to know these.

I think this is rhodosudomonas. And this is, let's see if I got it written down. I do, yes.

Rhodomicrobium vanellii is on the left, rhodosudomonas is in the middle, and rhodosudomonas, these are both rhodosudomonas, so I was right, different species. These are all members of the alpha, beta, or gamma proteobacteria. So really interestingly, The proteobacteria is this really large group of genetically similar organisms by 16S ribosomal RNA, but the capability to photosynthesize is kind of distributed throughout the group in certain genre.

There's not like a special isolated group. They do their photosynthesis, the electron donors will be hydrogen sulfide. Hydrogen or organic acids such as malic acid or succinate, right? They will oxidize sulfur to sulfate and they'll obtain their carbon from CO2 organic acids or carbon monoxide.

One of my friends in graduate school was doing research on rhodobacter soroides and he was, or rhodosporin rubrum actually. You don't need to remember that. But he was trying to demonstrate. Their ability to grow in the presence of carbon monoxide, so he had to grow these huge vats of these bacteria. It was this giant fermenter that was, you know, eight feet, you know, eight, seven, eight meters tall, right?

And they had a light in the center of it, and they had to feed carbon monoxide in it. But they had to be very careful not to feed too much carbon monoxide, so it bubbled out. And one time in the lab...

Everybody started feeling nauseous and it's like they had turned the carbon oxide up too high. So fortunately I wasn't in the lab that day. So here's what you it's very easy to isolate these guys.

You can take water from Lake Mendota and you just put it in a medium that has succinate in it and make it anaerobic. Succinate cannot be fermented. And then you expose it to light. The only thing that will be able to grow that...

Are these bacteria? And you can get all different species, and these are just some examples of vials I pulled after letting these incubate for about two weeks in the presence of light. One thing that's really interesting about the purple bacteria is they can grow under, they are not limited to photoautotrophy.

They can grow photoautolithotrophically on CO2, hydrogen sulfide, and light under anaerobic conditions. But they can also grow with carbon monoxide as their carbon source. They can grow photo-hetero-organotrophically.

Using succinate as their carbon source and their source of electrons, but using light as their energy source But you can also just grow them in plain old media You can streak these out on media and grow them in the dark and they'll do grow just fine As long as you provide a carbon source and they can grow on all sorts of that things in fact, the purple bacteria are pretty versatile they can grow on sugars and Alkanes and all sorts of crazy stuff that you can give them that makes them great model systems for doing research in this area. Okay, so they're light-hypersensing complexes. Their photosystem is housed in an intercytoplasmic membrane, an ICM.

So this is a transmission electron micrograph and they've taken the cell and like sliced it down the middle. And you can see that their membranes, there's little tubes that are pushed into the cytoplasm. to expand the membrane so that you can put more of these light harvesting complexes into the membrane. You have peripheral light harvesting complexes, you have core light harvesting complexes, and they surround the reaction center as we showed in the diagram earlier. Right, so we talked about how light goes around and around, it goes through the cytochrome BC1 complex.

pumps protons across the membrane. The one thing that we didn't talk about is how do they get reduced electrons, right? So the energy source, these do not have a high enough electron potential to actually, after they get to the quinone, donate the electrons to NAD to P to make NADPH.

Okay, so that if you under standard conditions, Quinones will not donate electrons to NADP. So what does these organisms do when they need reducing power? They do something pretty amazing. They take advantage of Le Chartier's principle.

They shut down the cyclic electron transport, so they stop pumping protons. So then reduced quinones build up to very high level, and it shifts the equilibrium. So now it can donate electrons to NADPH, or NADP.

So I thought that was worth mentioning. Not going to test you on that, but I think it's a really interesting thing that they can regulate where the electrons go and shut off electron transport when they need more NADP, or the proton pumping when they need more NADP. Okay. The other group is the green bacteria.

The green bacteria, unlike the purple bacteria, are obligate phototrophs. They only grow photoautotrophically, right? They harvest light via the chloroform. And unlike, again, the purple bacteria that are scattered throughout the proteobacteria, the green bacteria will cluster into a distinct group. And they are not closely related to other phototrophs.

If you take their 16S ribosomal RNAs, you sequence them and you line them up in a tree of life, they will all cluster together in one group. I've given a bunch of examples of the different organisms, and you know they're kind of neat to look at. Some of them will actually accumulate sulfur globules.

Outside the cell, some will accumulate sulfur globules inside the cell, but I don't expect you to remember any of these names. I am going to focus a little bit on the chlorobaceae, which are green sulfur bacteria, and talk about their physiology as an example. Okay, these are strict anaerobes. They can only grow under anaerobic conditions. They are obligate photoautolithotrophs, and their electron donor...

All can use hydrogen sulfide. Some can use hydrogen gas or thiol sulfate as their source of electrons. But in the environment, they're probably using a lot of hydrogen and hydrogen sulfide. All right, the reason I'm focusing on them is they have a very interesting light harvesting complex.

It's called a chlorosome. Now, this diagram is a little bit upside down, right? The outside is here.

The inside is here. So this is under the membrane. Light hits this, and it's absorbed, and it's focused then on the reaction center right down here, right?

It's just under the cytoplastic membrane. And the bacterial chlorophyll C that's in here is not in a protein. This is a lipid membrane, right?

It's encased in a lipid coating. And this is a crystalline array. And this array is very sensitive and very good at collecting photons.

So it's a very efficient light collector. And because of that, these green bacteria can grow in places that are very dim. There isn't a lot of light, but they can still get enough to grow. So chlorosomes do not have proteins in this structure right here in the chlorosome, but they have like a crystalline array of chlorophyll. Okay, if you look at them, here is the chlorosome next to the reaction center.

You have this core polypeptide. You have a light harvesting protein, you have a C-type cytochrome, and then you have, again, a BC1 complex. So what happens is the electrons go through these chlorophylls, they dump onto a quinone again, the quinone goes out to the BC1 complex, and you get this cyclic electron transport that pumps protons across the membrane.

Now... The way they have things arranged, the electron actually is of high enough energy by the time it gets down to NAD that it can make NADH without any kind of special exceptions. Okay, so that's that. Finally, we have the cyanobacteria.

And this is from a Nature article that was discussing the cyanobacteria at Yellowstone. Here's the hot... spring at Yellowstone, and you can see the water here is greater than 95 degrees, and see that it's blue, there's no life. But as soon as it starts to cool down, it's about 75 degrees centigrade, you get these bacterial mass, and they're growing at 75 degrees centigrade, and then they get pretty abundant even at 65 degrees centigrade. And that green and red, that is cyanobacteria.

So that's pretty amazing. These are ubiquitous in the environment. You will find them in deserts, in tropical rainforests, oceans, and even thermal hot springs.

They are gram-negative, they are obligate phototrophs, and they do oxygenic photosynthesis. This is plant-like photosynthesis, as we talked about, and they form a very tight phylogenetic group, right? They cluster all together in a phylogenetic tree. Their light harvesting complex is a little different, but it's the same idea.

You have the photosynthetic machinery in thylakoid membranes, and you have phycobilly proteins, and you have different ones. Phycorethrin, outside, phycocyanin, next, and alpha-cyanin, allophycocyanin, I should say, right next to the reaction center. And as you can see, you're starting with shorter wavelengths, higher energy, and it's transferring down through. and then focused on the reaction center.

Why have these different wavelengths? So you can collect more different wavelengths of light. When you have these three different proteins here, you can collect everything from 550 to 650 nanometers.

And it all gets focused on the reaction center. And again, the arrangement of the proteins with the higher energy light collectors on the outside, and the lower energy on the inside allows efficient energy transfer to the reaction center. Okay, here's the reaction center. This is a, interestingly, if you sequence the proteins in the green reaction center and you compare them to photosystem 1 in cyanobacteria, there is a significant amount of homology.

If you sequence the purple reaction center and you compare that to photosystem 2 In cyanobacteria, there is again a significant amount of homology. There are different numbers of proteins in chemistry, but there's homology there, and it suggests the hypothesis that the cyanobacteria arose when these two complexes transferred into one microorganism. Okay, for this one... I have a little animation.

Okay, here's all the different complexes. All right, here we go. Here's photosystem II.

Electrons go in here. They go to plastocyanin, or they go to this the cytochrome BC1 complex like, goes to plastocyanin, goes through, and then this goes through. This is non-cyclic photosynthesis here, right, going from here, photosystem II to photosystem I.

This is cyclic photosynthesis here. Right? In both cases, protons get pumped across the membrane. Okay, that is... Photosynthesis.

What I want you to do, and this will be the last exercise we do today, is I want you to compare retinal based phototrophy to photosynthesis. What are their similarities and what are their differences? So write down as many ideas as you can come up with.

Thank you. Okay, we got about a minute left, so here I'll give you the answers that I came up with. Right? Similarities, they both use a proton gradient.

They generate ATP versus ATP synthase. They have photopigments and a membrane is required. Differences, photosynthesis has a reaction center.

Photosynthesis has light-harving complexes. Retinal has a retinal-based phototrophy, right? RBT is one protein.

The photo can generate and reduce NAD to NADPH. The photo can fix carbon dioxide. All right.

See you Wednesday.

Transcript for:Microbes and Photosynthesis Insights

Transcript for:
Microbes and Photosynthesis Insights