Basically you need to show 3 things in a simple DNA model: phosphate, ribose sugar and the nitrogenous base. And it should connect something like this...
P for Phosphate
S for sugar
B for base
P****P
|****|
S-B-B-S
|****|
P****P
|****|
S-B-B-S
etc [Note: * means nothing just filling up the space cause the diagram came out retarded]
Notice for B there is for possible base A,C,T,G
A pairs with T and
C pairs with G
so maybe in your case, use different type of pasta to represent different things and join them together like that diagram above. Then put a key to it.