The Secret Life of Genes
Ask Science unravels the confusion between genes, DNA, chromosomes, genetics, and other technical terms that are thrown around in science news.
Lee Falin, PhD
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The Secret Life of Genes
We talk a lot about genes, but sometimes it can get a little confusing distinguishing between genes, DNA, chromosomes, genetics, and other technical terms that are thrown around in science news. So today let’s take some time to unravel the confusion.
Once Upon a Time…
Once upon a time, deep inside your cell, was a little molecule called adenine. Some people pronounced his name like add-eh-nin, while other people called him add-eh-neen.
But his closest friends just called him Addy.
.
Addy was pretty happy with his job. He was a nucleotide, one of 4 different types (and in his opinion, he was the best type). The other types of nucleotides were cytosine, guanine, and thymine, but Addy’s mother had always insisted he grow up to be an adenine, like his father.
As a nucleotide, Addy’s main job was to bond with other nucleotides to form DNA, or deoxyribose nucleic acid, the most important molecule in the universe (he admitted that this was a rather subjective opinion, but probably true nonetheless).
Chromosomes
One of the things that Addy liked most about being a part of DNA was how orderly it all was. Early in his life, Addy had been assigned to his chromosome, a massive DNA molecule nestled snugly inside the nucleus of a human cell. Addy always felt that he’d been fortunate to have been assigned to chromosome 17, a close knit group of about 78 million nucleotides.
Of course, just like most of the other chromosomes, there were two copies of chromosome 17: one from the organism’s mother and one from its father, but Addy privately thought he was on the better copy.
Some of Addy’s neighbors felt like chromosome 17 was a bit overcrowded; but whenever Addy heard them complaining about the tight space, he’d just remind his friends how lucky they were not to be stuck somewhere like chromosome 1, which had over 247 million nucleotides, three times as many as they had in chromosome 17.
Still, some of them would lament that they hadn’t been lucky enough to be on one of the other 23 pairs of chromosomes. “Look at chromosome 21,” they’d whine. “Only 46 million nucleotides. So much room to spread out!”
If Addy had possessed eyes, he would have rolled them. Sometimes the other nucleotides forgot that their chromosome, just like all of the others, spent most of its time as a long, stringy mess inside the nucleus.
It was only when the cell was getting ready to divide that the DNA would wind itself up into the long, cylindrical shapes that most people pictured when they thought about chromosomes. (If people thought of chromosomes at all these days.)
Genes
But Addy thought that the reason most of those nucleotides grumbled so much was because they were bored. Only about 2% of nucleotides in the entire collection of chromosomes were part of the elite collection of DNA responsible for encoding genes. Addy didn’t like to brag, but he’d been part of that elite group ever since he first joined chromosome 17.
Addy, along with about 20,000 of his nucleotide colleagues, formed one of the best genes in the cell. The purpose of their gene was to teach the cell how to build a pretty famous protein called p53. You probably read about it, it’ been in all the papers, responsible for cancer suppression and the like…a really important protein. And without Addy and his friends, it wouldn’t exist.
Whenever the cell needed more p53 protein, it would send someone over to Addy’s gene to copy down the instructions on how to make it. You might wonder why they had to copy instructions each time, well the weird thing was that the instructions were actually destroyed in the process of making the protein. Addy didn’t like to criticize how other parts of the cell worked, but he thought it was an awfully inefficient way to go about things.
Proteins
Addy could still remember the first time this happened – seemed like only yesterday. There was a commotion going on somewhere down the line of DNA from where their gene started. A big molecule named RNA polymerase (though he insisted they just call him, Art) had showed up, asking for a copy of the instructions to make p53. Of course they’d been happy to oblige him.
So Art had walked down the line of nucleotides that made up the gene and made a copy of each one. This might seem like an odd way to retrieve instructions, but the fact was that Addy and the other nucleotides which made up the gene didn’t just know the instructions for making p53, they were the instructions for making p53.
For whatever reason, running a copy of their exact sequence through the cellular machinery (a process the higher-ups referred to as translation) would end up forming a protein. Addy could think of more efficient ways to make proteins, but he didn’t ask questions. He had a job to do.
Conclusion
So hopefully that story helped unravel some of the tangled mess of jargon used to describe DNA. To review, our friend Addy was an adenine nucleotide, one of 4 different types of nucleotides that make up DNA molecules.
Each of your cell has 46 pieces of DNA, which we call chromosomes. 23 of those come from your mother and 23 from your father. A small fraction (about 2%) of those chromosomes have the important job of encoding genes, the sequence of instructions which tell the cell how to build proteins.
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Genetic structure image courtesy of Shutterstock.
