Tag: DNA

The DNA bases are now fully colored: red with green and blue with yellow. Green and blue are always the longer bases. The ends of each base pair are hidden behind the topmost strands of DNA backbone.

How to (correctly) draw DNA

Hello good friends! Here are two fun facts about me:

The combination of these two items means I get very (very) bothered by incorrect rendering of DNA.  Would you like to know how to draw DNA correctly?  Well, you are in the right spot.  Let’s get started.

Draw an X.  It should be 1.5 times wider than it is tall.  If you are drawing by hand, use a ruler.  The proportions are important here.

A black 'X' which is 1.5 times wider than it is tall.

Now draw a lot of Xs on top of that one, so you get a nice ziggity-zaggity pattern.

Seven Xes arranged vertically, stacked so that they touch and make a criss-cross pattern.

To illustrate my next point, it’s important to tell the two strands apart, so we’re going to use our magic poof button and color one strand red and one strand blue:

The same zig-zag pattern as before, but one zig is red and the other zag is blue.

poof

Right now the spacing between the two strands is exactly even, but that doesn’t happen in real DNA.  Perhaps you have heard of the major and minor grooves.  Well, we’re going to move the red strand down about 50% of an X-height so that there is unequal spacing between the two strands1:

There are still two vertical zig-zags, one red and one blue. They are slightly vertically offset to represent the major and minor grooves of the DNA.

Voila!  Now we have our skeleton to start drawing the DNA ribbons.  For each leg of the DNA, we’re going to draw a ribbon shape over top it.

The red and blue strands are now at 50% opacity. An s-shaped ribbon segment is drawn in black over one of the straight lines on the red strand of the DNA skeleton.

Practicing drawing consistent squiggles for your ribbons; I find the more evenly I can draw my ribbons the better the finished product looks.  Draw ribbons for both strands.  I like to do one strand first and then the other.

As before, the skeleton zig-zags are at 50% opacity. The same S-shape has been copied, rotated, and translated so that a full black ribbon covers the red strand from top to bottom. The X-skeleton is no longer shown. Ribbons for both the red and blue strands are completely drawn; they have been color-coded red and blue to help differentiate which strand is which.

Now comes a really fun part!  We’re going to erase some of the lines to show which parts of the strands are on top of the other strand.  BE CAREFUL.  There is a wrong way to do this.

Allow me to explain.  There’s this idea in chemistry called chirality.  The fancy definition for this is “non-superimposable mirror images.”  Let’s break that down for easier digestion.  “Mirror images” is easy enough to understand.  If you take a molecule and swap it left-to-right, you have its mirror image!  Easy peasy.

What about “non-superimposable”?  That means that if you take the molecule’s mirror image, no matter how you rotate, translate, or send wishful vibes at it, it won’t match up perfectly with the original.  A good example on the macro-scale is a pair of gloves.  You have a right glove and a left glove, and they can mirror each other, but you’ll never get them to stack on top of each other perfectly.  In chemistry, we actually use the terms “right-handed” and “left-handed” for molecules, to illustrate the exact same concept.

Chirality is very important in biology.  Sugar is chiral:  one mirror image will feed your brain, the other will do absolutely nothing for your body.  It’s even more important with pharmaceuticals:  often one enantiomer2 will save your life and the other is poison.  No bueno.

DNA is a chiral molecule.  That means that how we choose which way the helix turns is important: one way you will live to see another day, the other and your complete genetic blueprint is lost.  Pay attention to the pretty picture:

The red and blue ribbons' insides are now filled opaquely, with less saturated red and blues. The twist of the helix is much more apparent: the strands in front go from right-to-left as they go top-to-bottom. A large arrow overlays the image pointing in the same direction.

This DNA is “right handed”: as the helix twists from top to bottom, the DNA twists from right to left.  That means that if you choose a strand in the front of the DNA, it should go top-right to bottom-left3 and NOT the other way around.

Whew!  That was a lot of work!  But now we have the DNA ribbons (aka backbone) completely drawn.  Next up: adding bases!  Let’s pencil them in:

The same ribbons as before are depicted, but without the arrow. Instead, ten base pairs are depicted. Each base pair is a rounded rectangle with a division 1/3 of the way across its length. The first and fifth base pair are depicted only as circles, over top where the red and blue ribbons cross.

There are some important things to note about the base pairs:

  • They come in pairs.  Each little log I’ve drawn represents two bases.
  • Some of the bases are longer than the others.  Each pair is made up of a short base and a long base.
  • There are exactly ten (10) base pairs per full helical turn.  Exactly.  The best way I’ve found to draw this is to put a little circle where the two strands overlap, and put exactly four base pairs in-between.  The circles won’t show up in the final drawing, but they’ll help you space things out.

Ready to finish up?  I’ve erased the parts of the bases that are covered up by the backbone, and colored them so they look all nice and paired up.  Remember that adenine (a big base) will always pair with thymine (a little base), and guanine (a big base) will always pair with cytosine (a little base).4  Color accordingly.

The DNA bases are now fully colored: red with green and blue with yellow. Green and blue are always the longer bases. The ends of each base pair are hidden behind the topmost strands of DNA backbone.

And now for something (slightly) different

Now, my dearest readers, you have all the tools to count the errors of the DNA depicted in Jurassic World:

Let’s tally the sins, shall we?

  1. This DNA is far too thin: it should be about half as tall as it currently is.
  2. The grooves are evenly spaced.  No major or minor groove.
  3. WRONG CHIRALITY!  Aaaaaah!
  4. I count ~20-24 base pairs per helical turn.  Neeewp newp newp.

And now we know why Addie wanted to flip a table during certain scenes of Jurassic World.  Or basically any time DNA is depicted in the media.  Don’t be that guy:  learn to draw DNA correctly.  (plz for me)

 


I adapted this tutorial from two places:

 

2017-01-03 Addie 1