Visualizing structural dynamics of thylakoid membranes
We found that stroma and grana thylakoids are connected at the grana margins by and Karen Davies, Bastian Barton, and Götz Hofhaus for scientific advice. Spatial relationship of photosystem I, photosystem II, and the light-harvesting . membranes in plants: quasihelical model of the granum-stroma assembly. A granum is a stack of thylakoids in the chloroplast. The stroma is the gel-like material that surrounds the grana inside the chloroplast. The stroma surrounds the grana, so that the products of the light dependent stage needed in the light independent stage can diffuse easily into.
And this right over here is considered a separate organelle. So you get this thing that looks like this, and I'll just do it the best that I can draw it.
What is the relationship between Granum and Stroma
And this right over here is called the endoplasmic reticulum. So this right here is endoplasmic reticulum, which I've always thought would be a good name for a band. And the endoplasmic reticulum is key for starting to produce and then later on package proteins that are either embedded in the cellular membrane or used outside of the cell itself.
So how does that happen? Well, the endoplasmic reticulum really has two regions.
- Endoplasmic reticulum and Golgi bodies
- What is the relationship between the granum and the stroma?
It has the rough endoplasmic reticulum. And the rough endoplasmic reticulum has a bunch of ribosomes. So that's a free ribosome right over here. This is an attached ribosome.
These are ribosomes that are attached to the membrane of the endoplasmic reticulum.
So this region where you have attached ribosomes right over here, that is the rough endoplasmic reticulum. I'll call it the rough ER for short. Perhaps an even better name for a band. And then there's another region, which is the smooth endoplasmic reticulum. And the role that this plays in protein synthesis, or at least getting proteins ready for the outside of the cell, is you can have messenger RNA-- let me do that in that lighter green color-- you can have messenger RNA find one of these ribosomes associated with the rough endoplasmic reticulum.
And as the protein is translated, it won't be translated inside the cytosol.
botany - Difference between thylakoids and lamellae in a chloroplast? - Biology Stack Exchange
It'll be translated on the other side of the rough endoplasmic reticulum. Or you could say on the inside of it, in the lumen of the rough endoplasmic reticulum. Let me make that a little bit-- let me draw that a little bit better.
So let's say that this right over here, that right over here is the membrane of the endoplasmic reticulum. And then as a protein, or as a mRNA is being translated into protein, the ribosome can attach.
And let's say that this right over here is the mRNA that is being translated. Let's say it's going in that direction right over here. Here is the membrane of the ER. This right over here-- and actually, the way I've drawn it right over here, this is just one bilipid layer. So let me just draw it like this.
I could do it like this. And this is actually, this bilipid layer is continuous.
It's continuous with the outer nuclear membrane. So let me just make it like that so you get the picture. And then at some point in the translation process, the protein can be spit out on the inside.
As it's being translated, it can be spit out on the inside of the endoplasmic reticulum. So this is the lumen. This is the ER lumen right over here. So we're inside the endoplasmic reticulum here.
Here we're outside in the cytosol. So that way you get the protein now, inside the ER.Chloroplast structure and function
Inside the endoplasmic reticulum, and it can travel through it. And at some point, it can bud off. So let's say, imagine the protein is right over here.
And the smooth endoplasmic reticulum has many functions, and I won't get into all the depth of how it's involved. But at some point that protein can bud off. So let me draw a budding off protein. So let's say this is the membrane of the endoplasmic reticulum.
And a protein, let's say, ends up right over here. And then it can bud out. So it could go from that to-- let me do that same color. It could go from that to that-- I think you see where this is going-- to that, and then to that. And then it could go to something like this. Now it has budded out. And when you have a protein, or really you have anything that's being transported around a cell with its own little mini membrane, we call this a vesicle.
So now it'll bundle up, and now it is a vesicle. Now, this vesicle can then-- let me draw some of these vesicles holding some proteins, so let me draw that-- can then go to the Golgi apparatus, which I'll drawn in blue right over here as best as I can.
So the Golgi apparatus. This is not-- obviously there could be better drawings of something like this. And then they can essentially do the reverse process, and they can attach themselves to the Golgi, oftentimes the Golgi body, named after Mr. Golgi who discovered this. And then the proteins, once they get into the inside of the Golgi body, then they essentially go into a maturation process so that they're ready for transport outside of the cell, or maybe to be embedded into the cellular membrane.
So this right over here is the Golgi body, or a Golgi body or Golgi apparatus. Here we demonstrate structural dynamics of thylakoid membranes by live cell imaging in combination with deconvolution.
We observed chlorophyll fluorescence in the antibiotics-induced macrochloroplast in the moss Physcomitrella patens. The three-dimensional reconstruction uncovered the fine thylakoid membrane structure in live cells.
The time-lapse imaging shows that the entire thylakoid membrane network is structurally stable, but the individual thylakoid membrane structure is flexible in vivo.
Our observation indicates that grana serve as a framework to maintain structural integrity of the entire thylakoid membrane network. Both the structural stability and flexibility of thylakoid membranes would be essential for dynamic protein reorganization under fluctuating light environments.
Photosynthetic organisms have developed flexible machinery for effective light energy use 12. In higher plants, cyclic electron transport is stimulated by the association of chloroplast NADH dehydrogenase-like complex with PSI When PSII is damaged, disassembly of PSII occurs after its migration from the stacked, appressed membranes, or grana, to the single-layer, stroma-exposed membranes, or stroma lamellae, where PSII subunits are replaced 20 Based on these facts, the structure and arrangement of thylakoid membranes have to be flexible for such protein reorganization to be taken place in response to changing light environments.
The structure and arrangement of thylakoid membranes have long been studied since the first observation using light microscopy by Hugo von Mohl in The grana inside chloroplasts are already identified by light microscopy as dense, dot-like structures Introducing electron microscopy has deepened our understanding of the structural complexity of thylakoid membranes, showing the remarkable architecture in which stroma lamellae connect to grana in the helical configuration 232425 Recently, electron tomography has determined the three-dimensional 3D structure of thylakoid membranes in higher plants 2728revealing the distinctive image of the junctional connections between grana and stroma lamellae.
Visualizing structural dynamics of thylakoid membranes
Intriguingly, the junctional slits where stroma lamellae connect grana show significant structural variations 2728reflecting the variability of the membrane structure. Therefore, to demonstrate the dynamic aspect of thylakoid membrane structure in vivo, the visualization by live cell imaging is essential. In this work, we used conventional confocal microscopy to observe chlorophyll Chl fluorescence structures inside chloroplasts.
Previous studies have already shown Chl fluorescence images of chloroplasts in various green algae and higher plants 29 Although confocal microscopy exhibits Chl fluorescence structure in live cells, the fine membrane structure is hardly visible by conventional confocal microscopy due to the diffraction limited resolution