Number 26: Jelly Baby DNA

A couple of weeks ago I showed you how to build a passable model of DNA with K'nex. Now for something tastier.

You'll need:

• 2 long sweets like Strawberry Lances or similar
• A few handfuls of soft sweets, like Jelly Babies
• About 10 cocktail sticks .

What to do:

1) Sort the jelly babies into colours. Keep four of the groups and eat the rest.

2) Pair up the jelly babies so that one colour always goes with another. e.g. red with green and yellow with purple.

3) Stick the pairs onto a cocktail stick like you are making mini-jelly baby kebabs.

4) The attach the jelly baby kebabs to the long sweets. Carry on doing this until you have something that looks a bit like a ladder.

5) Pick up your ladder and give it a twist.

Hey presto a model of DNA made from sweets!

So what does it all mean?

DNA contains the information needed to build a living thing. That info is recorded in the form of four bases called adenine, thymine, guanine and cytosine (usually abbreviated to A,T,G and C). In my  model each of the coloured jelly babies represent one of these bases. So lets say yellow is A, purple is T, green is G and red is C. In DNA the base T always pairs up opposite A, whilst C pairs with G. And to represent that I  paired yellow with purple and green with red. 

The DNA molecule then twists up to form a cork screw like (helical) shape, hence the twist I gave it at the end.

Our model of DNA represents just a tiny fragment of a real DNA molecule. In reality DNA could be billions of bases long (and I couldn't get hold of that many jelly babies).

Number 24: K'nex DNA

60 years ago James Watson and Francis Crick were busy trying to figure out the structure of DNA.  So to celebrate the anniversary I thought I'd come up with a series of DNA related activities.

Watson and Crick eventually worked it out the structure by building models of the molecule and comparing them to X-ray pictures collected by Rosalind Franklin.

Watson and Crick built their model from bits of lab equipment and other odds and ends. You can see just how cobbled together it is if you visit  London's Science Museum. Which just goes to show that even Nobel prize winners use whatever they have to hand.

The model shows that DNA is made from two intertwined helices. Sort of like two corkscrew shapes wound around each other. Each helix is made from a backbone of sugar-like molecules bound to phosphates. Then each helix is zipped up to its partner via something called basepairs.

So what else could we use to build a model of DNA? How about K'Nex?


You'll need:

A load of these three K'nex peices (or similar)

These will represent the 3 main parts of DNA. The green pieces are going to be the sugars, the white bits are the phosphates and the blue ones are the base pairs.

To make 1 complete turn of K'nex DNA you'll need 14 green bits, 14 white and 7 blue bits.

What to do.

1) Connect up the 3 green pieces with the 3 white pieces and then 3 green pieces with 4 white pieces, so you have two sections that look like this.

2) Add the blue pieces onto the green pieces, like so.

3) Here's the tricky bit. Connect up the blue pieces to the other section like this.

You should end up with a twisted bit of k'nex model that is starting to resemble the double helix of DNA. 

4) Now just continue to build more of the same and link them together to form as long a strand of k'nex DNA as you can!

The model you've built isn't quite accurate but its still shows some of the important features of DNA. Most importantly it's a double helix  and you might notice that it's also got grooves running around the double helix. One of these is narrower than the other. These are known as the minor and major grooves , DNA has them as well.

If you want to do more DNA related stuff with K'nex you can buy the official model kit or have a look at this great site from Mount Sinai University.