DNA, Protein, and Existential Crises

/in , /by

I explained in an earlier post that your DNA is a manual for how to make you.

A fundamental principle about genetics is that you are born with your specific edition of the DNA manual, and you are stuck with it, whether you like it or not.  The DNA book can’t be edited.  The cells that are reading the book can’t revise and print a new edition.  It’s a one way street.  The information goes from DNA to protein.  DNA doesn’t really care if protein has a better idea of how to do things.

If you inherit a typo in your DNA manual, there it stays.  (Although, the goal of “gene therapy” is to replace the pages with typos.  But that will have to be another post, sorry.)

The flow of information from DNA to protein is sometimes called the “central dogma” of biology.  I don’t refer to it as such, but teachers and textbooks seem to have taken a real liking to the term.  The central dogma in part explains why traits acquired during one’s life won’t be passed to the next generation.  Again, the DNA book can’t be edited by experience.  
So I was merrily going through life with this absolute rule in my head: DNA to protein.  Never the other way around.

But as my high school biology teacher used to say, “always and never are never true in biology.”  

DNA can be changed.  
mind… blown….

Not the sequence exactly, but portions of DNA can be turned “on” and “off.”  From what I’ve read, this only happens during fetal development.  The uterine environment can alter the baby’s DNA.  Not by editing carefully, fixing a typo here, adding a paragraph here.  No.  It’s more like ripping pages out.

I didn’t realize how much comfort I found in the absolute rule that DNA-to-proteins provided me until I discovered this exception.  I felt like someone took my blankie away.  But I have learned my lesson: never get too attached to rules when it comes to biology.  There’s always some cheeky exception.  While I was a little shaken by the news, I was comforted by the simple fact that this is just really cool.  There is a system built in that could in theory prepare a fetus for the world it will be entering.  There are several assumptions at work in that statement, but the idea is tantalizing. 

Most unfortunately, I’ve only heard of detrimental in utero DNA-switching effects.
When a pregnant woman smokes cigarettes, she can actually alter her baby’s edition of DNA to give the baby asthma.  If the fetus is a female, and therefore has her eggs, the next generation, already stored within her, that DNA can be affected as well.  So if a woman pregnant with a girl smokes enough cigarettes, her grandchild will have asthma too.  The gravity of this news weighed on me.

My god, we can ruin two generations at once?!  We’re not supposed to be able to change anything about DNA, and you’re telling me I can alter my grandchildren? Zaaaa!!

If the feedback was going to help the new addition to the world, it would go the other way around.  If a woman was smoking, it should send messages to the baby that “Hey, the air out here is really bad.  You better be able to deal with this.  Make yourself some super lungs.” But then women would have incentive to smoke while pregnant, so I guess the universe works after all.

Survival of the Sickest: The Surprising Connections Between Disease and Longevity (P.S.)I have also heard that if a pregnant woman is eating nutritionally poor food, the baby will be underweight, even if the mother is overeating.  In Survival of the Sickest, Sharon Moelem theorizes that this could be adaptive in the sense that it’s telling the baby, “Hey, there’s no good food out here, so don’t show up hungry,” hence, tiny babies.

This is relatively new information, so the exact mechanism isn’t fully understood, nor is the full list of signals that can turn genes “on” or “off.”

While I gave two negative examples here, that doesn’t mean this only works to that effect.  As we learn more, this phenomenon could explain how huge evolutionary steps could be taken in relatively few generations.

The fact is we often learn how things work by observing what happens when they don’t work.  The road to understanding human biology is paved with disease, injuries, and genetic disorders.  I mean, our understanding of neuroscience for the longest time was based on observations of people with head injuries.  You take what you can get, and that often means learning about the bad stuff first.

Anyway, this discipline that studies how DNA can be turned “on” and “off” is called epigenetics.  Isn’t it just awesome? I know, right? (That was for you, Sharin.)