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0:13
Welcome back to the lecture series on bioenergy, so we are in the module two and we have finished first two lectures where we talked about, the overall scheme of,
0:28
processes which happens in photosynthesis. We describe the light reaction and the dark reaction
0:36
and we talked about photosystem one, photosystem two and the electron transport, and the proton gradient which is created across the thylakoid membrane. So at this stage,
0:52
all my viewers and listeners have an overall idea of what are the processes which are happening in photosynthesis. Now, next two classes what we will do so today, we will be starting our eighth lecture. Now, next two or two-three classes our idea will be to explore each one of those processes, in greater detail so that
1:17
what all the next generation of technologies which are evolving by getting inspiration from them can be clear to all of you. So let us get back to the slide today. We are in to that lecture 8, so essentially in the module 2
1:46
and this is basically this is the third lecture of module 3 by 2. That is why you did like this okay. So now if you remember the first very first reaction what we have dealt with was co2 + h2o making ch2o plus oxygen as a by-product.
2:12
Now fairly early in the 18th century, this reaction was discovered but this, this reaction was not discovered in one shot, there are few landmark discoveries or you can say landmark events which led to the discovery of the photosynthesis. So we will just
2:37
in couple of minutes, we will kind of highlight them that will give you an idea of the timeline when this discoveries did happen okay. Now add one more component to this, was the role of light which is light driven reaction so, if we look at it, it was the evolving of oxygen,
3:01
this part this was by Joseph Priestley
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just putting the name you can cross-check you can go online, and you can figure it out,
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and around 1780, the next major discovery which happens was the role of light,
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which was described by a Dutch scientist his name was Jan Ingen Hous
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so who discovered the role of light. The third one was Jean Senebier so his discovery was with this carbon dioxide what he essentially says let me just put the name Jean Senebier showed that
4:04
co2 is taken up
4:12
in photosynthesis. I am just putting PS for photosynthesis not putting the whole name, then came the role of water out here you see, just in a different color code for your understanding,
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role of water was basically shown by a guy called Theodore De Saussare.
4:40
What he said that he demonstrated that some of the weights of the organic matter produced by plant and of the oxygen evolved is much more than the weight of co2 consumed. And based on the law of conservation of mass by Lavoisier, he predicted that this is nothing but the water okay. And all these so you see Joseph Presley here this is around 1780, very similar Jan Ingen Hous worked at the same time, Jean Sengbier just soon after that and the Theodore De Saussare who talked about
5:18
the role of water and the final contribution was made by Julius Robert Meyer, Julius
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Robert Meyers. So what Meyer says was the plant take in one form of power that is light and produce another form of power called chemical molecules. So essentially it was completely summarized by Robert Myer who said that it is a light energy is converted into a chemical energy. And if you will see it very clearly this is what is happening out here, this is the chemical molecule which is generated and in other words
6:04
this is also a process, natural process of carbon sequestration or carbon capturing because in the environment there are lot of carbon dioxide. So what you are essentially doing, you are capturing the carbon dioxide or the carbon molecules and converting them into big carbohydrate molecules, in other words, you can call this whole process.
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Let me okay, this whole process could fall under
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carbon capturing or carbon
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sequestration which is one of the very emerging challenging field currently that how we can
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sequester lot of this carbon dioxide in the form of air pollutant which are present there. But this brings us to a very different perspective to this whole thing if there is a way one can emulate the photosynthetic apparatus then essentially
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one can think of making food in an artificial chamber. Think of it you have carbon dioxide is in abundance your water in abundance in the sea or the oceans and what you need and you have light in abundance all your three commodities are in abundance. Now if you can push them in one apparatus which will make carbohydrate as the way a chloroplast does. And what we are talking about is that you do not need to grow food in the field, you actually can grow food in a small chamber.
8:01
So these are the kind of dream what mankind is seen in other words, you can actually form biomass if you know what really photosynthesis is doing. So think of it why I am putting thrust on this whole area is that the whole biomass formation is directly related
8:25
to the photosynthetic output which is happening on the floor of Earth as long as the solar energy is available to us. That is why now what we will do from this point on our next journey will take us talking about the architecture of the organelle which is chloroplast.
8:49
We will talk about the structure of the chloroplast, on next slide we will move on to the structure of chloroplast okay, before I draw the structure try to visualize
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those of you have seen Food Corporation of India godowns or something. You must have seen that
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there are gunny bags filled with grains they are stacked over one another like this at some point or other all of you have seen this, if not in real life or at least in a picture, you have seen it okay. We are stacked over one another and there is a closed room inside which these grains are being kept, exactly visualize a similar structure chloroplast is a double membrane structure before I draw this try to visualize in your brain is a double membrane
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structure. In which you will see stacking of those something like a gunny bags all over and there are connected between them so now let me draw it what I was trying to tell you. It will be something like this, so the structure is this is outer layer something like this,
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a structure which dimension is around 2 to 3 micron and on it we will see something like this these are those gunny bags which are present there, the connectors, like this, okay.
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So now that is was telling you try to imagine where the grains are kept in gunny bags and these are those gunny bags that will kind of help you to visualize how the structure really looks like,
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like this now if we label this a structure let us put the labeling to them. So this is the, this is the inner membrane and putting the
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inner membrane
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then the yellow shading what I am doing, this is the
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outer membrane so two envelopes in a membrane and the outer membrane then you have something these structures are called thylakoid membranes.
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So if you see the cross section of the thylakoid membrane
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so you must have seen a pillow. So imagine you have the cover of the pillow cover and you remove the cotton from it or any kind of cushioning agent. So it is something like this so if I had to know coming back to the slide if you see this structure very carefully this is structure will be something like
12:15
so there is a hollow part out here this part is hollow okay. So thylakoid membrane is kind of
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inflicted it is kind of you can say it is a saucer-like inflated structure there are saucers like this and underneath it is hollow. So and they have a different function that is why and all these structures asymmetric in other words if you look at the outer periphery, so that is why I am putting different colors. So if this part and this part, inner and outer they have a different property, in property in the sense, their molecular
12:55
arrangement of the different kind of proteins which are present there is entirely different, so most of the biological membrane. What we know off till this day are a symmetric in nature
13:16
and this asymmetry helps most of them to achieve some very unique functions okay. So now coming back to the slides out here, so there are a few other things what we have to mark here, so we talked about the thylakoid membrane and this is spacing between what you see is called
13:41
thylakoid space
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okay. Then these kind of connectors are called stroma or lamellae
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okay and then there is a space in between these two which is called inter membrane space
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okay and this empty space was you see is called stroma, so, overall this is the
14:28
whole architecture of the chloroplast where these reactions are taking place and if you
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guys remember, so, where this photosystem one and photosystem two is located, now, just let me point out in, so photosystem one and photosystem two is kind of suppose this is the inner membrane like this is connecting like this. So now,
14:52
this is where the photosystem one and photosystem two, water splitting clusters all these things are
15:00
decorated around. So, what you see essentially is that so this is where all the
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PS1, PS2 water-splitting and all these things are located, so if you see it is essentially a
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energy transforming membrane where the lighter energy is falling and electrons are ejected and all the phenomena what we have talked in the last two classes it is all happening at that site,
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so this is and that of course if we look at the dimension. So we are talking about a dimension of around you know
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5, 4 to 5 micron and the max or maybe less and within that 4 to 5 micron, much, much smaller are these the smaller units where these kind of reactions are taking place,
15:56
so that was telling you that if one can emulate even ten percent of this kind of structures and make energy harvesting then, pretty much all our global energy problem will be solved,
16:12
this is the kind of challenge where mankind is heading, could we emulate a chloroplast or could you emulate thylakoid membrane,
16:23
is it really possible maybe someday, somewhere okay. So this is the overall architecture which what I want you guys to know kind of you know keep in mind and if you see wanted to know the composition of it the composition is something like this they nearly have equal amount of lipids and proteins okay,
16:44
almost equal amount of equal amounts of lipids and proteins
16:57
and most of the lipids and the total lipids if you look at it, so there are Galactolipids,
17:08
you have sulfolipids and you have phospholipids. These are the different kind of lipids which are present there, so, this is overall and of course, I have already mentioned you that one second,
17:35
this structure also has its own genetic material
17:41
have already mentioned, and that is one of the reason why people say, let this at some point in evolution was and stand-alone organelles which for some XYZ reason
17:57
parasitized and other animals. And today what we see is the plant evolved because of that okay, so, coming back so the next thing what we will be dealing with is once we are done with it so this is what we have talked about now we will talk about the structure of the chlorophyll so, so the chlorophyll molecules how they look like, so, I told you that there are similarities between chlorophyll and hemoglobin told you that
18:26
if you remove the iron from the centers of the porphyrin ring or then it becomes yellow because the whole porphyrin is yellow, similarly, if you remove the magnesium which makes the chlorophyll then it remains as yellow the very moment you put magnesium, it attains the green color, the very moment you put iron it attains the red color okay. So now let us see the structure of the chlorophylls, the light trapping pigment,
18:59
structure of
19:07
chlorophyll, so, the structure of chlorophyll is something like this, you have a coordination
19:18
out here you have the magnesium sitting out here, like this and
19:30
this is the porphyrin structure it is a complex of structure but just follow it, it will you see a lot of symmetrical features in the structure
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okay. Similarly, you have
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okay,
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okay, and in this corner you will see a CH and a methyl group present here,
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then the methyl group present here and there is something called an R. I am just putting it R here that are essentially stand for one second bit
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that are essentially stand for two situation if it is one second if it is CH3 then it is so there are two kind of chlorophyll then it is chlorophyll a and if it is CH 0
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then it is chlorophyll b, okay. So these are the two chlorophyll generally used in very small letter, just correct that chlorophyll b, out here another methyl group present here at this point you have complex structure out here where you see
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carbon and CH3 and out here you have an oxygen attached to it on the other side
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okay. So of the plane, you have a methyl group, hydrogen out here under hydrogen and out here this is where the second level of modification comes
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and there is something called an R this R is again very important for you guys to keep tap and I will talk about the R just in few minutes and it is one small
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this, this bond is wrongly placed here actually this should happen here.
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So now you see this complex structure and I have not explained you about R what that R stands for now what I will do just follow up this pictures. And let us put what that R means in the next slide, so that R is equal to
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CH 2 CH another CH 3 CH 2, CH 2, CH 2, CH then of the CH3, CH2 twice and here you have CH2, CH2,
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CH3, CH3 so this is what the R group stands for, so, what we have talked about is, there is a chlorophyll a and a chlorophyll b based on that particular position. Where we talked about where
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whether it will be CH0 or it will be a CH3 now we will talk about what distinguishes a chlorophyll a and chlorophyll b let us coming back to the slide, so, this is the second R group. What we have talked about, so, there are two zones one R group I told you out here the box top and the other R group out here which I shown in all right okay. Now so what you see is the absorption spectra, so, if you if I draw the absorption spectra it
24:38
will be it will look like something like this okay. So here you have absorption coefficient
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which is shown in mole and say around out here 10 to the power 5 and absorption 400,
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500, 600 and ending at 700 these are in wave length in nanometers okay.
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So, for chlorophyll a, if you look at it
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we put it in green so for the chlorophyll a the absorption peak is something like this
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if you see this is what is the chlorophyll is absorption is going
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okay. Now if you look at chlorophyll b which I am so let me just this so, this is chlorophyll a and for chlorophyll b you see the absorption it is something different it will be something like this it is slightly shifting and
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so one second let me put this, chlorophyll b okay. So what you observe is that and there is a slight staggering in the wavelength at where chlorophyll a and chlorophyll b are absorbing but what is interesting to know that there are a huge vast part of the spectrum where there are no absorption. These are the peak absorbed done which are taking place at that particular wavelength, now to summarize this particular slide, it
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is so what we are observing is that the absorption spectra of chlorophyll a b and b are different. So
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absorption, these are the take-home message absorption spectra of chlorophyll a and b
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are different this is the first conclusion you have to draw from this and secondly
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light is not appreciably absorbed by chlorophyll-a at 460 nanometer that you can see at 460 nanometers light is not appreciably absorbed by chlorophyll-a
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whereas it is captured by chlorophyll b which has intense absorption at that wavelength. That you can see out here so if you see it around 460 nanometer, so there is a better absorption of chlorophyll, chlorophyll b as kind of to as compared to chlorophyll a
28:12
and these two kinds of chlorophyll complement each other in absorbing incident light okay. So this is the major take-home message and the spectral region from 500 to 600 nanometer is only weakly absorbed by this chlorophyll that you can see out here as far as trying to tell you in the beginning. So if you look at this zone
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there is hardly any kind of absorbance which is happening at that region okay.
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But this does not pose a problem for most green plants okay by contrast light is often limiting factor for cyanobacteria or blue-green algae, red algae the poses accessory, so for such
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blue-green algae or the red algae for them there are other accessory molecules which Nature has devised which ensures that they absorb light at those kind of different kind of wavelengths. So having said this let us summarize this, so what we have observed is that there are two kind of chlorophyll, chlorophyll a and chlorophyll b and their absorption spectra is slightly started but there is a huge shown between 500 and 600. Where there is hardly any kind of absorbance which
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is taking place but apart from it there are several accessory molecules which are available to different species whether it is a blue-green algae, cyanobacteria, red by red algae or whatever
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they are supplemented with a series of such different dyes which absorbs wavelengths at different wave which absorbs light of different wavelengths. So in other words, if you have to kind of imagine it, it is to be something like this as if there are different kind of say you know. So this is the solar energy which is falling on different kind of life forms and they have a different kind of you know,
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so, wave length, one wave length two, wave length three, wave lengths four, five.
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So Nature has equipped most of the life forms with wide array or spectrum of light harvesting pigment by virtue of which it complements the existing panels of chlorophyll a and chlorophyll b but this particular aspect is an inspiration for one of the advanced topic. What we will be dealing with is called dye-sensitized solar cells we will be
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dye-sensitized solar cells we talk about this later, but at this stage, just remember there are wide array of such pigments available in nature. So these are the if I these are the different pigments or natural pigments and dyes
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available in nature which otherwise have a role to support the
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living systems which are there, but those could be an inspiration to develop different kind of another series of solar cells okay, we will come later into this, so, this is the overall understanding what I wanted for you people, for chlorophyll a and chlorophyll b but what is the significance of this chlorophyll a and chlorophyll b. So I will close in here thank you.
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