Estimates vary, but some scientists believe that the DNA found in just one gram of cells
can store up to 455 exabytes of data. To put this into perspective, based on an average
computer storing 500 gigs, you would need nearly one billion computers to store that
same amount of information digitally. Pound for pound, when it comes to storage capacity,
man-made technology simply does not come remotely close to what DNA is capable of.
So how does it work and how do we even know how it works? In today's lesson, we'll explore this
topic as we describe how DNA was discovered, explain its structure, and evaluate how this
structure relates to DNA's function of storing information. Let's get into it.
When Friedrich Miescher accidentally discovered DNA, or, deoxyribonucleic acid, in the 1860s, the
function of this molecule was unknown. It was not until 1944 that Oswald Avery confirmed that DNA is
the genetic blueprint, or, instructions, for our cells. However, because it is so small, scientists
had a very difficult time understanding its structure or how it worked. Fast forward to 1951,
and scientist Rosalind Franklin took pictures of DNA using a special method involving X-rays.
Using these pictures, scientists James Watson and Francis Crick proposed a theory that explained
DNA structure. Remember, a theory is a scientific explanation that is backed by a lot of evidence,
and Watson and Crick's model for DNA is still used to this day.
What they proposed is that DNA is a double-stranded molecule
that is shaped like a double helix, which is a structure that looks like a spiral staircase.
The genetic instructions are stored in nitrogen bases, which form these steps of the staircase.
There are four nitrogen bases in DNA and they are adenine, thymine, cytosine, and guanine,
which can be abbreviated as A, T, C, and G. These bases are always bonded in pairs within DNA, with
A always bonding with T, and C always bonding with G. The order of these nitrogen bases determines
how a cell operates, what resources are built, and how many. You can think of these sequences of A,
T, C, and G as the language of DNA, kind of like the order of letters written on a page
has meaning, or, how the order of ones and zeros, or, binary code, is the language of computers.
The genetic codes that make life possible are incredibly complex, so there can be
billions of these nitrogen bases in just one cell. Now, I don't know about you, but if I
needed instructions on how to build something and my instruction book had billions of pages,
I'd never get anything done. Luckily for us, our DNA has an incredible organization system that
helps our cells stay on track. For starters, DNA is integrated into chromatin, which is a
thread-like structure made out of proteins called histones and DNA. The protein helps pack the DNA
so that it can be neatly folded and made available when it is needed by the cell. Additionally,
all of this chromatin is divided into large sections called chromosomes. A chromosome is
a structure made out of chromatin that helps cells better organize genetic information. Chromosomes
come in pairs of two and humans usually have 23 pairs for a total of 46 chromosomes.
You can see the visual representation of an organism's chromosomes using a karyotype,
which is a map of the number and appearance of all of the different chromosomes in an organism.
Scientists use karyotypes to better understand how DNA is organized in living things.
It is important to remember that while DNA is stored in the nucleus of our cells and other
eukaryotic organisms, single-celled prokaryotes, organisms like bacteria, don't have a nucleus,
which means their DNA floats freely in their cytoplasm. Prokaryotes can get away with this
lack of organization because their genetic code is way simpler than that of eukaryotic life forms,
often consisting of just one single chromosome's worth of DNA. Ah, to live such a carefree life.
Okay, we have now covered the basics of DNA structure. We've learned that many scientists
have contributed to our understanding of how DNA works, including Rosalind Franklin, James Watson,
and Francis Crick. Additionally, we've learned that DNA is shaped like a double helix, or, spiral
staircase, with its sequences of nitrogen bases forming the steps of the staircase. The order of
these nitrogen bases is the language of DNA and determines which resources are made by the cell.
We've also learned that DNA is bundled up into a structure called chromatin,
which helps keep the information stored in DNA organized. And this chromatin can be further
organized into chromosomes, which are mapped out visually as karyotypes by scientists. Finally,
we've reviewed that only eukaryotic organisms store their DNA in a nucleus while prokaryotes
let their DNA hang out freely in the cytoplasm. in our next lesson, we'll take a deeper dive into
protein synthesis, which is how DNA tells our cells what resources to make. Until then, I'm
Caroline, and remember, life is full of wonders so keep learning and don't ever stop wondering.