In this episode of Tiny Show and Tell Us, we break down the complicated science of tides and why some places have massive tidal swings while others do not. We also cover the role of ancient viral DNA in our genomes, and how it seems to be making us less susceptible to cancer treatments like chemotherapy.
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Transcript of this Episode
Sam Jones: Welcome to Tiny Show and Tell Us, the bonus series where you write in with your favorite science story, fact, or piece of news, we read your email aloud, and then dive deeper. I'm Sam Jones, the exec producer of Tiny Matters, and I want to give a big thank you to science writer and chemist Anne Hylden for doing the research for this episode and so many episodes before it.
Today I'm here again with science communicator, George Zaidan.
George Zaidan: Hey, Sam. Great to be here. Before we get into things, just a reminder that Tiny Matters is always looking for you to write in because that is what makes future episodes possible. You can email us at tinymatters@acs.org, or click the Google Form link that we put in the episode description.
All right, let's do this. Now, you went first in episode six-
Sam Jones: I did.
George Zaidan: ... so I can volunteer as tribute this time.
Sam Jones: Lovely.
George Zaidan: Our first one comes from Will, so Will writes, "Did you know that the largest tidal swing in the southeastern United States is in coastal Georgia? During a king tide, the difference between low and high tide can exceed 10 feet. This is due to something called the Georgia Bight," that's spelled B-I-G-H-T, not B-I-T-E, "where a lot of the wave energy from North Carolina down to the tip of Florida flows inwards toward the Georgia Coast. Since the continental shelf extends further out into the ocean than most other states, the waves are smaller, but the tides are much bigger." And then Will shares a link for context.
Sam Jones: First off, can I just say 10 feet? That's wild because I grew up near a river, was not the case. It's like a whole story-
George Zaidan: It's a whole story-
Sam Jones: ... of a building.
George Zaidan: Exactly. It's a whole story of a building. I think for me, I think we just got to start with the tides, because tides, they're way more complicated than most people realize. Now, most people know two things about the tides. This, I knew this, they're caused by the moon, and there's two per day, right? Two high and two low. I watched some videos online to try and figure out what causes the tides and how the causes the tides, and there were no satisfying explanations until I found a video on a channel that I want to shout out because it was really good. It's called Waterlust. It explains the whole thing.
I'm going to give you the super condensed version of it. Unless you are driving right now, listening and driving, close your eyes. Picture the Earth on the left and the moon on the right, and picture them just still being held by large, invisible hands. In real life they're orbiting each other, but this is just a simplified picture.
If those hands let go, the Earth of the moon will be pulled toward each other because of gravity, right? How did you picture that happening? Did you picture two billiard balls moving towards each other?
Sam Jones: Yeah.
George Zaidan: Okay, so let's complicate that picture.
Sam Jones: Oh, no.
George Zaidan: I know.
Sam Jones: I like how also you started off by being, "I think people feel like they understand tides," and I was like, "I'm not one of those people," so let's do this.
George Zaidan: Okay, so gravity gets weaker the further away something is right. This is the wild one. Gravity affects every point on earth independently. What that means is like gravity is pulling on the oceans, gravity is pulling on the lands, gravity is pulling on the trees. It's not that gravity pulls on Earth as a whole, it's that gravity pulls on technically every single atom on Earth independently.
Close your eyes again. Go back to the picture of the Earth and the moon being held by invisible hands, right? Picture the moon's gravity, pulling on all the different points of Earth. Just to simplify it, let's talk about four different points. The point where the earth is closest to the moon.
Let's say that that's some ocean and some land. Do you think that gravity will pull strong there or weak there, the moon's gravity?
Sam Jones: I would think it would be stronger.
George Zaidan: Yes. That'll be the point where it pulls the strongest because closest to the moon.
Sam Jones: Yeah.
George Zaidan: Now think about the opposite point of Earth, the furthest left point in your mind, the gravity there will be...
Sam Jones: Less.
George Zaidan: Weakest, right? Exactly.
Sam Jones: Yeah.
George Zaidan: Now, this is the tricky one. Imagine the top and the bottom of Earth in your mind.
Sam Jones: Oh, no.
George Zaidan: Yeah, I know. Remember that the moon is a lot smaller than earth. What will those points of Earth do, the top and the bottom?
Sam Jones: I'm going to sound so dumb when I say this, like pull centrally?
George Zaidan: Yes, pull. No, that's exactly right. So the top-
Sam Jones: Wait, that's so weird.
George Zaidan: I know. The ocean at the top part of the Earth will be pulled towards the moon, which is down and to the right in your mental image. The opposite will happen in the bottom of the Earth. The ocean will be pulled up and to the right, right?
Sam Jones: Yes.
George Zaidan: And now let's add one last piece of the puzzle, I promise, is the rock of Earth, the solid part of Earth, not the oceans. That is going to get pulled towards the moon, but because it's rock, it's not going to get deformed like the ocean.
Overall, what happens is that all these different parts of earth that accelerate toward the moon at different rates, so the ocean on the right side of Earth is going to bulge outward toward the moon. The ocean at the top and bottom of earth are going to be compressed downwards because they're being pulled down towards that tiny spot of the moon.
This is the most confusing one. Because the rock of Earth is moving towards the moon faster than the ocean on the left side, the ocean on the left side gets left behind relatively in space, so it bulges out.
Sam Jones: Weird.
George Zaidan: You really need an animation to understand this.
Sam Jones: We'll link to this video for sure so people can really look at it.
George Zaidan: I highly recommend it. Overall, the oceans of Earth become an ellipse, and you have the sphere of the rock that rotates inside of this ellipse. That gives you two high tides, which are the bulges on the left, and two low tides, which are the compressions on the top and bottom.
As if that were not complicated enough, other things in our solar system also cause tidal forces. The sun will also cause, so you get overlapping tidal forces of different celestial bodies and you get very, very complicated tides. High, low, sometimes you get two times a month where the tides are extra high and two times a month where they're extra low.
And that's not even considering coastal geography. Will's whole email was like the Georgia Bight has exceptionally high tides, a difference between high and low tide in the southeastern United States. That's basically because, we're going to super shorten this explanation, you have a bay. It's a very, very large bay, and the rising water gets concentrated, the high tide, gets concentrated in the center of that bay, and so you get exceptionally high and low tides.
The same sort of thing happens in the place with the highest tides on Earth, which is the Bay of Fundy in Canada. That is amplified by a whole other thing. That's resonance, that we're not going to get into. It's all covered in this video, which we will link to. But from thinking that I understood tides now I'm like, "Wow, I really don't know a thing about tides, actually."
Sam Jones: I think I was always afraid of trying to understand tides, but this actually makes me feel better, George. Thank you. That was a good explainer, and thank you to whoever made that video. Also must've been a good explainer. Now I know it's not magic.
No, I never thought it was magic, but I think I was always like, oh, this is just... A lot of stuff that has to do with space really confuses me for some reason. Deboki and I sometimes talk about this where we're like write a script that relates to something in space or answer a question and we're always like, "Good job, good job. I know that was hard for you mentally." And I think because I knew that the moon was involved, I was like, "This is going to mess with me and I'm not going to understand it." I feel like most things if I don't understand them, I'm so dedicated trying to figure it out. And for some reason with tides I was like, "Can't do it."
And now it makes more sense. Of course there's always more questions and answers with these kinds of things for me, but it actually makes a whole lot more sense than whatever I was trying to assume it was in the past.
George Zaidan: Yeah.
Sam Jones: Yeah.
George Zaidan: I think that the thing that trips most people up is like, okay, you know that the moon pulls on the Earth's oceans. So then why does the ocean on the back of the earth, far away from the moon, stick out away from the moon? Shouldn't the moon be pulling that toward itself, too? That's the thing that really trips most people up, and this was the best explainer I've ever seen on that front.
Yeah, we'll link the video. It's great. You should watch it. It's 14 minutes about tides, but who doesn't love to go deep?
Sam Jones: Yeah, for sure. Awesome. Well, thank you, George.
George Zaidan: Sure.
Sam Jones: I'm going to talk about something completely different that I'm less afraid of-
George Zaidan: Excellent.
Sam Jones: ... which is odd because I'm going to talk about ancient viral DNA. Okay, so this one, this email was from listener Rick from Broomfield, Colorado. Rick wrote in sharing news about how ancient viral DNA seems to help cancer cells grow and survive in the face of treatments like chemotherapy.
He was actually inspired to write in after hearing a Tiny Show and Tell in episode 65, where actually I shared work showing that a lot of this parasite called an amoeboid parasite, a lot of its DNA — almost, I think the majority of its DNA actually — comes from these really large ancient viruses. And so Rick saw that or heard that and wrote in saying, "I have to share this news about how ancient viral DNA seems to help cancer cells grow and survive treatments like chemo."
George Zaidan: That's wild.
Sam Jones: Let's talk about this ancient viral DNA, more human endogenous retroviral elements, or HERVs. I don't know if people in the field call them HERVs, but it's H-E-R-V-S, so I'm calling them HERVs. Apologies to cancer researchers if that's not how you guys do things, but we're going to shorten it, so HERVs. So I think really this requires a short explainer on what it means for something to be endogenous and what a retrovirus is.
George Zaidan: Please.
Sam Jones: First, retroviruses. These are viruses that can use their RNA genomes, so their genome made up of RNA, but they can use it to actually make DNA. Typically, we have DNA codes for RNA. In this case, the viruses will actually get their RNA into a cell and then trick the host cell into expressing that as DNA to make viral proteins. And so they hijack the cell's machinery, use it against itself to make copies of a virus. Very sneaky.
Real bummer because so because that new DNA is now present in the nucleus of the cell, it can be replicated and carry on each time the cell divides. That's why retroviruses like HIV can't be eradicated from a patient. Once they're infected, they can only be controlled because they're in there. They've integrated into your genome. What happens is HIV gets in, a protein called reverse transcriptase, it actually transcribes the viral RNA into DNA. And then that DNA is brought into the cell nucleus where your chromatin is, which is really just like your bunched up DNA. HIV has this protein called integrase, and it integrates the HIV DNA into your DNA.
And so this is very similar. I mean, depending on what the virus is, there's going to be variations in what proteins or enzymes are playing a role in that integration and the other processes to lead to the integration.
And then when we talk about endogenous, because again we're talking about human endogenous retroviral elements or HERVs-
George Zaidan: HERVs, yep.
Sam Jones: Yes, the word endogenous refers to something that arises from within an organism. For example, if someone says, "Oh, endogenous expression of a protein," it means your cells are producing that protein.
Back to HERVs. These are bits of viral DNA that have been incorporated into the human genome, even though they originally of course came from viruses. These leftover bits are sometimes simply called endogenous retroviruses or retroviral fossils, which I actually like that.
George Zaidan: Yeah, that's a great name.
Sam Jones: Yeah, yeah. They make up about 8% of our genome.
George Zaidan: What?
Sam Jones: Yeah, which is a lot more than I thought.
George Zaidan: Wow.
Sam Jones: Yeah, yeah, yeah. Just because they make up 8% of our genome doesn't mean they do things, but it's still... That's a lot of real estate.
George Zaidan: I mean, I remember hearing at some point that the difference between two different species can be a couple percent of DNA, and so this is way more than that. Wow, okay.
Sam Jones: Yeah, which is fascinating. Actually it's interesting that you just mentioned because a cool fact for you, endogenous retroviruses provide some really compelling proof that humans and chimpanzees shared a common ancestor since we have many of these bits of viral DNA in the exact same places in our genomes.
George Zaidan: Wow, okay. That is super fascinating.
Sam Jones: Yeah, yeah, and so I just hinted at not all this is super important. Some of it's considered "junk" DNA, but some of it does serve functions in our body like placenta formation and some immune response stuff as well.
There are a bunch of different studies articles that have looked at HERVs' roles in human health. Researchers have found that stretches of viral DNA that are embedded in the human genome can produce proteins that actually can help block infection by viruses.
George Zaidan: What?
Sam Jones: Yes. Yes, yes, yes.
George Zaidan: Why? How?
Sam Jones: It's pretty wild. I wonder if it was a thing where it was a viral survival. There's so many viruses that other viruses compete with that that's... That's where my brain goes.
George Zaidan: It's almost like...
Sam Jones: Survival of the fittest virus?
George Zaidan: Yeah, and people who come into a house and they're like, "Okay, done. Nobody else can survive here. We're going to arm the security system." That was a really weird metaphor. I don't know why I went there.
Sam Jones: Yeah, it's like Last of Us viruses.
George Zaidan: What's Last of Us?
Sam Jones: The Last of Us?
George Zaidan: I don't know what that is.
Sam Jones: The show/video game that it was adapted from that was like a sensation?
George Zaidan: I don't. I don't really...
Sam Jones: Wow, George.
George Zaidan: I don't video game because when I was a kid I got addicted to them and it was bad. And so I quit.
Sam Jones: I don't video game, but they turned it into an HBO series and it's incredible. They won a lot of awards. It's probably one of my favorite things I've ever watched. But it is scary. It does involve some zombies, but it's essentially about a pandemic that's caused by a fungus. I can't believe that we're having...
Okay, we have to get back to retroviruses. George, you need to look up The Last of Us after this. Go watch it.
George Zaidan: I'll go watch it, okay.
Sam Jones: Where were we?
George Zaidan: I feel like I've interrupted you 16 times in this.
Sam Jones: It's okay. It's okay. Retroviruses, HERVs, we're getting back to Rick's news. Researchers of the University of Colorado at Boulder have found a link between HERVs and cancer cell survival. Cancer cells, they're already known to express a lot of genes that they're really not supposed to, and that's part of what makes them dangerous. It's just not entirely clear what's turning on that expression. Why are they doing this? It turns out that viral DNA could actually be playing a role.
And so what this group did was they analyzed data sets of gene activity in 21 different cancers, and they looked specifically at activity in these ancient viral sequences, these HERVS. And then they did an experiment using CRISPR to cut six of those sequences out of colorectal cancer cells just to see if there would be any effect if you took those out in these cells being more susceptible to treatment.
In removing one of those sequences in particular, it seemed to turn off a DNA repair sequence. That made the cancer cells more likely to die by DNA damaging therapy, including radiation. That's part of the thing is these cancer cells, I mean there's so much variation and it depends on the cancer, but a lot of times it's like these cells are... What is the right word for it? They're tough, right? They have these mechanisms that normal cells wouldn't to prevent die off. And so they have these proteins and things that will actually help with DNA repair. You hit them with radiation and there's stuff in there that would repair.
What these researchers are finding is that some of the sequences that are coding for things that make these cells so tough, if you get rid of them, they will be easier to kill off. In those sequences, not always, but it seems like a lot of them come from this viral DNA that's integrated.
George Zaidan: Fascinating.
Sam Jones: Yeah, and so learning more about gene expression and cancer cells could really pave the way for more targeted therapies in the future that would make standard therapies like chemo work more effectively.
If you knew you were coming up against some virally encoded protein that's going to make immunotherapy or chemotherapy less successful, could you also block that protein? Or could you find a way of silencing the expression of endogenous retroviruses themselves?
It's very exciting. It's one of those things where you're like, "I don't understand. Why are these cells not responding? This should be killing them." But you have these ancient sequences of viral DNA that are helping those cells produce proteins that are then making it so these therapies are less effective. How can we mess with that is what researchers are now thinking.
George Zaidan: That's super cool. It's especially cool because it sounds like this experiment in one stroke illuminated something fundamental about what's happening and also provided maybe an avenue for us to make our cancer treatments better.
Sam Jones: Yeah, absolutely.
George Zaidan: Very cool.
All right, that's it. Thanks for tuning into Tiny Show and Tell Us, a bonus episode from Tiny Matters, a production of the American Chemical Society.
Sam Jones: To be featured in a future episode, send us an email with your tiny show and tell at tinymatters@acs.org, or click the Google form link in this episode's description. See you next time.
- Video: How tides really work
- Bay of Fundy: the home of the world's largest tidal range
- Where is the highest tide?
- Learn about the Georgia coast and its unique tidal ecosystem
- Human endogenous retroviruses in development and disease
- Switching Sides: How Endogenous Retroviruses Protect Us from Viral Infections
- Human endogenous retroviruses: our genomic fossils and companions
- Origins and evolutionary consequences of ancient endogenous retroviruses
- Ancient viruses fuel modern-day cancers
- Endogenous retroviruses mediate transcriptional rewiring in response to oncogenic signaling in colorectal cancer
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