glycolipids

Glycolipids are another molecule that you find in the cell membrane, and so I'm going to circle one right here. Um, this one here is a glycolipid, so I'm going to write that down here: glycolipid. So, um, again, we can divide this into two. Glyco, glyco is to do with sugars, um, saccharides, and then lipid is to do with fats. So again, that this is, um, a molecule, a name made of two different types of molecules stuck together: a sugar type of molecule from the glyco part and a lipid type of molecule.

So then that's what we see in the structure of the molecule. This molecule has a chain at the top of sugars stuck together. Again, this is an oligosaccharide, it's a short chain. Here's one over here. Look, the green bit poking up is the oligosaccharide, that's this part here, and this oligosaccharide is glued to some lipid tails. You see how it's got like fatty acid tails dangling down? So this is another one of those kind of hybrid molecules, similar to a glycoprotein. The glycoprotein with sugar attached to protein, this is a glycolipid, so it's sugar attached to a lipid. But you can see they look a little similar. They're embedded or kind of, um, stuck in the membrane because of, in this case, because they're tails that the hydrophobic tails like to be amongst the other hydrophobic parts here and away from the water. And then the glyco part, this little chain, is the bit that sticks up a bit like an antenna, like the antennas that we saw for the glycoproteins.

So what is the role of a glycolipid? Well, again, it's a little bit like a glycoprotein and in that is to do with recognition, recognizing or receiving information from the outside. But it's not an actual receptor per se, it's more what we call a marker. It's like a, um, like a name tag for a cell. So, for example, you might have a nametag that says, "Hello, my name is Rachel." This might say, "Hello, I'm one of Rachel's cells." This one might say, "Hey, I'm a liver cell." So taken together, these two tags would say, "Rachel's, Rachel's liver cell."

All right, so why do our cells need to have markers like this? Well, one reason is that your immune system needs to know what belongs to you and is friendly and shouldn't be attacked, and what is foreign, what doesn't belong, and what you need to attack and get rid of. And so your cell, your body relies on these markers to determine what is self, what, what it should be here, like what's a name tag that makes sense, and what's something that we don't recognize.

And another thing is you also need inside your body to recognize cell types. So if you've ever seen like a surgery or something and seen inside of someone's cavity, like the abdominal cavity, everything in there is jammed in tight. There's intestines, and there's a liver, and there's a spleen, and a pancreas, and kidneys, and it's all smushed up together. But when they open up somebody, these parts are separate, like they're not all glued together in one solid mass. The liver is not glued irreparably to the kidneys, they're two separate items. So how does the liver cell know not to stick to the kidney cell, but it knows that it should stick to other liver cells? And that's what they, one of the reasons cells have these markers. So if two liver cells go up to each other, they can detect each other's markers and like, "Okay, you're liver. Okay, you're liver. We should stick together. We're going to build a liver." But if the liver cell comes up against the kidney cell, they can say, "Okay, well, we're both Rachel's cells, so that's okay. But I'm a kidney, you're a liver. We need to not glue ourselves together." And so that's one of the roles of these, of these markers.

This also goes a little bit towards, um, sometimes in a cancer diagnosis, someone will have a tumor biopsied, and it may be a tumor in like the lung or in the femur, like in the big bone in the leg. But the oncologist may say, "This is a metastasis. This is the spreading of a cancer from somewhere else." And you might say, "Well, how'd you know? How did you know this didn't start in the bone and it is a bone cancer?" And they can look at markers on the cancer tumor cells to say, "Okay, well, this, this marker is not a marker that belongs in a bone cell. This is a marker that comes from breast tissue, for example. So maybe this is a metastasis, a spread from a breast tumor that has now lodged itself in the bone, but it originated in breast tissue." So these markers have diagnostic values and they have various roles in, in your body. But that is a glycolipid.