In this video, we're going to introduce chloroplast structure. Chloroplasts actually have two membranes, just like the mitochondria, and so the chloroplast is going to have an outer chloroplast membrane and an inner chloroplast membrane. Now, unlike the mitochondria, which does have folds and cristae in its inner mitochondrial membrane, the chloroplast membranes do not have folds or cristae, and so neither of the chloroplast membranes have folds or cristae. If we take a look at our image down below, we can get a better understanding of the chloroplast structure. Notice on the left-hand side, we're showing you a micrograph of these plant cells and notice that each of these green structures represents a chloroplast. If we zoom in, notice on the right we're showing you a typical representation of a chloroplast. The chloroplast has two membranes; they have an outer membrane that goes around the entire perimeter and then an inner membrane as well. Notice that the inner membrane, unlike the inner membrane of the mitochondria, does not have any folds or cristae.
Within the chloroplast, specifically in this region right here, you'll notice that there are these green pancake-looking structures throughout, and each of these green pancake-looking structures are actually referred to as thylakoids. The thylakoids can be defined as interconnected pancake-shaped sacs made of membranes found within the chloroplast. It's also important to keep in mind that these thylakoids are hollow on the inside and consist of a membrane, but inside the thylakoid is a hollow space called the thylakoid space.
A stack of these thylakoids is referred to as a granum, and the plural form of granum is grana. The grana are really just referring to stacks of thylakoids. The granum can be thought of as green pancake stacks within the chloroplast. There's also a region known as the stroma that is important; it is the innermost region of the chloroplast, and so the stroma is going to be analogous to the mitochondrial matrix. The stroma is going to contain chloroplast enzymes, chloroplast ribosomes, and chloroplast DNA as well. The chloroplast is going to have its own independent DNA that's separate from the DNA of the nucleus and is also going to have its own ribosomes and enzymes, separate from the enzymes and ribosomes of the rest of the eukaryotic cell.
This concludes our brief lesson on chloroplast structure which is going to be important to keep in mind as we move forward in our course, especially when we get to talk about photosynthesis, since the chloroplast is the site of photosynthesis for plant cells. I'll see you all in our next video.