*Note to readers: Enjoy this previous article by Dr. Jack Brown, who is on vacation this week.
Anthropomorphizing is attributing a human characteristic to something that is not human. It is often a mistake to do this, but it can be used as an effective example to drive home a complex topic.
In attempting to explain the central dogma of molecular biology, I often say DNA is “self-aware.” All information flows from it. DNA directs everything about itself, the cell it is housed in, and the structure, function and behavior of the organism it makes. It even directs that organism to pass it into future generations, ensuring its survival, while the organism perishes.
The process of passing on the DNA can get complicated and costly, just ask a male praying mantis. Passing on the DNA may have cost him his life but biologically speaking, it was worth it. The chicken is just the egg’s way of making another egg.
Explaining why I would call a molecule “self-aware” takes only one story. To make a new cell of any kind, the cell’s DNA must first replicate itself, providing the new cell with a copy of the DNA code. The key in that sentence is “replicate itself.” A major principle of the central dogma is that DNA directs its own replication. The proteins that will do all the work of copying the DNA were made by the DNA.
For DNA to copy itself, it must first be unzipped. DNA exists as two complementary strands base paired together (A-T & C-G). An enzyme (protein) called DNA helicase has the duty of breaking up the A’s from the T’s and C’s from the G’s, thus unzipping the DNA. Once DNA is unzipped, it naturally wants to recoil to get the base pairs back together. So it must be held open by tiny proteins called single stranded binding proteins.
Now that DNA is unzipped and held open, the copying of the code is run by multiple enzymes. Known as DNA polymerases, they do the job of copying the two separated strands, doing their best to ensure the rules (A-T & C-G) get followed to the T, pun intended. One strand of the DNA, called the leading strand, is copied continuously while the other, lagging strand, gets copied in fragments pulled out in loops. The details of the strand differences can be explored online, but if you take a major in biology with me one day you can expect an essay question on this, so heads up! The side that gets copied in fragments must have those fragments sealed back together, and of course, there is another enzyme to do just that — DNA ligase.
I have not described all the enzymes involved in copying DNA, but I do hope you get the point. The enzymes that unzip, hold open, copy and edit DNA are all made by the DNA, which directs its own replication.
I encourage you to Google a few other enzymes involved in DNA replication, primase and topisomerase. Exploring http://biologicalphysics.iop.org/cws/article/lectures/47042.html by Dr. Richard Berry of Oxford can help expand and explain the topic.