One of the problems that science textbook authors face is the fact that science is constantly changing. As we learn more about the Creator’s handiwork, we find that the science we have taught as fact is actually incorrect. Sometimes, this is because the experiments upon which those facts are based were in error. Sometimes, it’s because our interpretations of those experiments were in error. Sometimes, it’s a result of making conclusions that go beyond what the experiments actually tell us. The practical upshot of all this is that some of the things you are reading in your science textbooks are wrong.
I recently found out that something I (and most other authors) have taught about DNA is probably wrong. Most people know that DNA is a double helix. As shown in the illustration above, those two helixes wind around each other, with the information-bearing units (called nucleotide bases) inside. In order for cells to use the information in DNA, those helixes have to be separated so that the sequence of the nucleotide bases can be read. That means the helixes need to be held together when DNA is not being used, and then they must be separated when it is time for the cell to read the DNA.
How does that happen? Well, according to most textbooks (including mine), it is because the nucleotide bases form hydrogen bonds with one another. Hydrogen bonds are weaker than true chemical bonds, but they can hold things together. As I say it in my textbook, Exploring Creation with Biology, 2nd Edition:
…the attraction between the atoms in hydrogen bonding is about 15% as strong as the attraction between two atoms that have a true chemical bond linking them. Thus, the hydrogen bonds in DNA are strong enough to keep the two chains together in a double helix, but they are significantly weaker than a true chemical bond. Since they are weaker than a true chemical bond, it is rather easy for the two helixes in DNA to unravel.
This sounds great, but a recent study indicates that it’s probably not true. If nothing else, it doesn’t tell the entire story.
The researchers showed that you can unravel the two helixes in DNA without forcing the hydrogen bonds to break. Instead, all you have to do is change the environment in which the DNA exists. If DNA is in an environment that is mostly water, the two helixes hold together nicely. This is because DNA is hydrophobic, which means it is repelled by water. The DNA stays together in order to avoid the water molecules as much as possible. However, if you add a chemical that makes the DNA’s surroundings more hydrophobic, the DNA will relax, because it doesn’t need to avoid as many molecules. If you make the environment hydrophobic enough, it will relax to the point that the helixes unravel.
Based on their results and results from other researchers, the authors suggest that there are enzymes in the cell’s nucleus that do exactly that. When the DNA is not being read, it is surrounded by a lot of water molecules, so the helixes stay tightly wound around one another to avoid the water molecules. When the cell needs to read a section of DNA, enzymes are brought near that part of the DNA. Those enzymes are partially hydrophobic, and the DNA relaxes. This allows the helixes to unravel so that the information can be read.
This research really surprised me, since I have used the textbook explanation over and over again throughout my years as a science educator. Because of this, I contacted a molecular biologist who is a part of my extended family. I don’t like to bother him too often, because he is retired, but he is one of the most accomplished, brilliant, and humble scientists I have ever met. I asked him if he would take a break from fishing and hunting to let me know what he thought of this “surprising” research.
He basically said that he didn’t find it terribly surprising. He said that years ago, his lab saw that adding a chemical called formamide significantly lowers the temperature at which you need to heat DNA to unravel the helixes. This was good for them, because they wanted to heat the DNA as little as possible. They assumed it was because the formamide was making the DNA’s surroundings more hydrophobic and therefore allowing the DNA to relax, reducing the energy needed to pull the helixes apart. They just never investigated the process to see if they were right.
Now this doesn’t mean the hydrogen bonds between the nucleotide bases in DNA are not important. They allow the bases on each helix to pair up properly, and they may aid in holding the two helixes together. However, the textbook explanation that they are the main reason DNA holds its double-helix shape when it is not being read is almost certainly wrong.
Science is a wonderful way to gain knowledge about God’s creation, but by its very nature, it is tentative. You must always be willing to reevaluate what you have been taught about science, because much of what you have been taught will eventually be shown to be wrong.