If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content
Current time:0:00Total duration:7:20
ENE‑1 (EU)
ENE‑1.B (LO)
ENE‑1.B.1 (EK)

Video transcript

when we study science its natural to just categorize a whole series of things it's just being really really unimaginably small so when people say hey atomic scale or molecular scale or protein or a cell you often just group that together and say oh those are really really really really small things but what I want to do in this video is get an appreciation that even though all the things I just mentioned are really small there's actually a huge difference in the sizes of those things and hopefully that'll give us an appreciation for how complex something like a cell can be how it can have all of this machinery how it can actually be a living organism or part of a living organism and so at this scale this is a this is my little rendering my drawing of a water molecule you have the oxygen atom in the right over here in this purplish color and then you have two hydrogen molecules bonded to it and this is going to be roughly 0.275 nanometers and just to remind ourselves a nanometer is a billionth of a meter and just to get ourselves an appreciation of that so let me so this is one billionth one billionth one billionth of a one billionth of a meter that's a nanometer and if you want to even attempt to visualize that that would be a millionth of a millimeter so one let me write this one one-millionth one millionth of a millimeter and I actually like using this one because a millimeter is about as small as as I can on a reasonably on a reasonable basis visualize but then it's at a millionth of that so this definitely goes well beyond at least my capabilities of visualization so that would be the diameter or the width of a of a water molecule but now let's go to the next scale up we've talked a lot about proteins and this is our friend the this is this right over here is our friend hemoglobin and just so you get a sense of scale the width of hemoglobin is going to be about five nanometers or five billionth of a meter now that seems super small so in some ways it's okay to categorize that into your super small part of the brain but it's good to appreciate this is much larger than a water molecule if a water molecule were on this scale I pre drew it this little thing over here that was that's my attempt at drawing a water molecule at this same scale so even when you go from something like a water molecule to a protein you're already going dramatically up in size and dramatically up in complexity and we've talked a lot about protein structure how can they can take on all these interesting shapes and do fairly surprising and complex things inside of biological systems but now let's go let's go the the next scale up and the next scale up I'm going to go to a virus and what I've attempted to draw here this is a fairly well-known virus this is HIV and it's actually one of the larger viruses and its diameter is roughly 120 120 nanometers so if we were to if we were to if we were to draw this hemoglobin this hemoglobin protein at the same scale as we've drawn this virus this thing right over here would be the hemoglobin protein and we wouldn't even be able to see the water molecule at this scale right over here but this is still really really small this is 120 billionth of a meter so this is this is still this this is this is still unimaginably small but now let's go up to the let's go up to the next scale so this creepy picture right over here this is a t-cell this is a depiction this is a if you want to see the whole thing that is a t-cell right over here this is a t-cell and this creepy picture this all the blue that's the t-cell and what you see in yellow that's the HIV virus emerging taking advantage of this t-cell so so that's why it's so creepy it's using that cells machinery to to reproduce itself but you immediately see on this picture how small the HIV virus is compared to the actual T cell each of these each of these small little things each of these small things is an HIV virus which we already saw is a lot bigger than something like a hemoglobin protein and so hemoglobin protein you wouldn't even be a you know on this scale maybe it would be a pixel if if that and on a similar scale as this t-cell you have a you have things like red blood cells and this is actually a comparison the side by side this is using an electron this isn't losing an electron microscope you see a red blood cell right over here and you see a T cell there roughly roughly on this the same the same size or at least the same order of magnitude size and a red blood cell is going to be six to eight micrometers micrometers wide so this is six to eight millionths of a meter so if we were to if we were to just take seven as the average seven millions seven seven millionths of a meter over here we're talking about a millionth of a millimeter now we're talking about seven millionth of a meter and just to get an appreciation for size we already compared the virus the HIV virus to this cell we're seeing it directly as they emerge from this cell but each of these red blood cells are going to contain roughly 280 million hemoglobin molecules so here so there's going to be 200 each of these there's going to be 280 million of these so 280 million that's not million million hemoglobins in each one of these so hopefully this starts to give you an appreciation for even though we categorize cells as these unimaginably small things they're actually far larger they're they're they're they're ginormous compared to things even like even like large even proteins and especially when you think of things on the molecular or the atomic scale and that's why cells are so interesting they actually have a lot of complexity to them but just have an appreciation also for house about how small cells are even though we've just described these red blood cells and these T cells there's you know there's these kind of worlds unto themselves there are these incredibly complex things if I were to if I were to draw the width of a human hair on this screen right now relative to the scale of these red blood cells it would be about as wide as this video so from if I want to draw a human hair it would go from there roughly to there there's actually a lot of variance in the width of a human hair but the width of a human hair would be just about like that if you look at the scale of if you looked at the scale of this picture right over here if you looked at these scales it would be much much much bigger and I encourage you you know we can think okay width of a human hair pluck a hair out look at it put it on a piece of paper it's hard to even discern the width but we're saying that that with compared to these these red blood cells would actually be here the entire width of the screen we've already said these red blood cells EC cells these are all comes with these are worlds unto themselves when you think of it from a viral or especially at a at a molecular scale
Biology is brought to you with support from the Amgen Foundation
AP® is a registered trademark of the College Board, which has not reviewed this resource.