Delivered on: 16 OCT 2023
The thylakoid membrane of a chloroplast is an internal system of interconnected membranes, that carry out the light reactions of photosynthesis. This lecture delves into the intricate structure of the thylakoid membrane, a key component of the chloroplast. The thylakoid membrane is a busy factory where the magic of photosynthesis occurs. It houses various protein complexes that work together to capture sunlight and convert it into chemical energy.
The lecture highlights the importance of the thylakoid membrane's organization. Different protein complexes, such as Photosystem II, Photosystem I, cytochrome b6f, and ATP synthase, are strategically located within the membrane to ensure efficient energy transfer and conversion. The lecture also discusses the role of light-harvesting complexes in capturing sunlight and passing the energy to the photosynthetic protein complexes.
By understanding the thylakoid membrane's structure and the functions of its components, we gain a deeper appreciation for the complexity and efficiency of photosynthesis.
Video Transcript:
Okay now we go deeper now into the thylakoid itself. So, you got your chloroplast then you got your thylakoid here. Now we go to the thylakoid membrane. So, it is a membrane okay we are talking deeper, okay?
I just want to to put things into perspective now you know the plasma membrane of a cell, right? Now you are inside the cells inside an organ in inside a membrane so there are many layers of inside, inside, inside, inside, this is super super super small.
Okay we are talking about maybe not nanometer we are talking about picometer right now so so so small okay.
When talk about membrane, thylakoid is also a membrane the important thing to know is that the thylakoid membrane contains this thing.
The integral membrane protein meaning that the membrane of thylakoid, I enlarge this okay there is a protein in here this is protein in here and this is called the integral protein.
Okay the membrane is made up of two lipid layers so this is lipid layer okay and the lipid layer when you enlarge this head and tail structure, phosphatidylcholine you will have the hydrophobic region sorry hydrophilic region, water loving region and the hydrophobic region.
Okay this thing here so this thing here is arranged in such a way there are some parts will be hydrophobic some part will be this is important because hydrophobic region repels water.
Okay repels water and it ensure that things do not get solubilized easily things do not get merged together.
Like the water right you have you have water you put one color in one color in later you get a new color because water is soluble. It mixes everything so this hydrophobic region prevents that from happening.
So that other structure can be present in it without being disturbed right okay. So, what do I expect you to know from here just that the fact that this is integral membrane protein.
Some protein actually only present on the surface you only get here okay some protein are only on this side some protein is actually attached like that.
So you can imagine that the surface of a membrane not only the surface of a cell any membrane is actually a very very busy area have imagine that this table is a surface of a membrane it's full of antenna it's full of holes it's full of gates. it's a b busy busy place.
It's like think of something I'm thinking I'm I'm thinking of a of of a busy maybe like a you know you know some urban area got boulevard by the side you got shops and then suddenly you got your trash can suddenly you got your hub to wait for your grab to come and and then there is a telephone to call the police in case you got chased by a bad guy and then there's also a place for you to jump to the next boulevard that kind of thing. It's a busy busy place okay and that also apply to the thylakoid membrane.
And then look at here. This is the thylakoid membrane this thing here that gets even deeper now super super zoom actually scientists do not have the image the actual image for this this is like a model of it they tried to get it but the image still looks fuzzy.
I think they have the microscope now to get all the deep in here but they reserve it for the NASA they don't want to release the image for us.
Okay so this is a thylakoid disc, you see it is connected. On the surface of the thylakoid disc the thylakoid membranes I want you to know these things there are four proteins that is involved in the photosystems in thylakoid membrane four proteins.
Photosystem 2, Photosystem 1, Cytochrome b6f and also ATP synthase these are all proteins. Remember you have um learn about the photosystem, right?
What is photosystem actually? Photosystem is actually protein it is a protein okay. It's not alone one protein no. It is a main protein structure and then other protein attached to it to make it functional.
Okay so you can see in this image here these are the labelling photosystem 2 one protein cytochrome B6f one protein photosystem1 protein, ATP synthase one protein then you will see the dimer here.
LHC1, LHC means light harvesting complex one meaning that this subunit of a protein is meant to be attached to since the number is one is meant to be attached to photosystem one here. That's why the labelling become like this. The cartoon version of it you have PS1 protein flanked or sandwiched by a pair of LH C1 dimer.
Dimer means the subunit got two components to it. Di- m
eans two MER- in science MER like polymer monomer and so on, the word mer means building block or smallest unit of something. So it can be anything monomer polymer dimer Trimer and so on. M E R yeah not Mur that's not it.
Okay and another thing that you need to understand here about the localization of the protein. This is very important localization of the protein you can read a bit more later. I can highlight here is that, remember that the lamellae. Lamellae means filaments because this tubing looks like a filament.
Lamellae, you got two types of lamellae now grana lamellae, stroma lamellae. That's what you have here the middle region here is the grana lamellae this the one that is taking here one 2 3 grana lamellae.
Then you got the edge of it before you found the stroma lamellae. It's very important to understand here that photosystem and the other two proteins the ATP synthase and cytochrome b6f they have what we call as protein localization.
Meaning that these four proteins do not appear randomly on the lamellae. No. They are actually concentrated in one places. For example, like this one photosystem 2, photosystem 2 you will find them predominantly in grana lamellae this one here.
This what colour. Is this I don't know can I complain to this book? Do proper colouring. How to call this colour this is green this is also green. Ah greyish green ah greyish green, brighter green yeah bluish green. okay bluish green so the bluish green the that is the photo system to you will see that they are only present in the grana lamellae predominantly.
Okay but the photosystem one together with its associated light harvesting complex LHC1, they are predominantly found in the edge of grana lamellae but more and more in the stroma lamellae. Very important.
Yes however for the cytochrome b6f in here, what colour is this? cyan I call it cyan for the cytochrome b6f the cyan, you can see that it's pretty much everywhere. It's here on this grana lamellae edge of grana lamellae and the ATP synthase.
ATP synthase is also present in a random distribution okay so why this is important? So that the energy transfer between these protein by energy I means electron. There are in the most efficient manner ever. Because this thing all these uh photosystem they will be activated somehow meaning that they receive energy.
In order to ensure that they get activated in the most efficient manner possible they need to be positioned in the strategic location. That's the reason okay.
Imagine if um…let's see I can make a hypothetical situation. Okay imagine if this photosystem one PS1 protein is located right in the middle of the folding here. Meaning that it's kind of dark and gloomy space in there it will not have access to the final molecule which is present in abundant in stroma. You see? photosystem one at the end of the road it needs to pass the electron to an electron acceptor molecule this molecule by the way it's called NADP+. It needs to pass eventually to this thing this thing will accept and becomes NADPH.
This NPDP+ is present in the stroma. Stroma is this region the…what colour is this? Yellowish light yellowish region if it's in here, can it have easy access to NADP? Not easy not easy so inefficiency will occur. That's why the design has been in such a way you photosystem one and your light harvester complex stay on the edge of grana lamellae or even better stay in the stroma lamellae. Get expose to the soap of the chloroplast so that when you are ready send electron to an NADP right away and then you get your reducing molecule.
Reference book: Plant Physiology and Development 7th Edition
by Lincoln Taiz, Ian Max Møller, Angus Murphy, Eduardo Zeiger
Full video: https://www.youtube.com/watch?v=dYs_TczAsM0
Attribution 4.0 International — CC BY 4.0 - Creative Commons
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