Course Icon


Biology Lab: AP Investigation #3 - DNA Sequences and DNA Modeling

SO Icon

Lab Exercise

Creating A DNA Model to demonstrae DNA replication

Concept: DNA replication is possible because of the unique double helix structure and limiting connections allowed by the pyrimidine and purine base pairs. Large two-ring purines take up more space than the shorter single-ring pirimidines. Cytosine and guanine require 3 H-bonds; thymine and adenine require two. So the only possible combination pairs are AT and GC.

Goal: To understand DNA sequencing and replication by investigating a mapped DNA Sequence.

AP Exam preparation -- Doing the AP version of this lab:

Please read through the 2012 AP Biology Lab Manual, Investigation #3: Comparing DNA Sequences to Understand Evolutionary Relationships with BLAST. Most of the materials are online and you should be able to complete the entire lab without a problem. If for some reason you are unable to do so, you may perform one of the alternate labs below, or you may decide to perform it in addition to Investigation #3.
There was no equivalent lab in the 2002 Biology Lab Manual.

Alternative Lab #1

If you are unable to complete AP Investigation #3, then if at all possible, perform the Illustrated Guide to Home Biology Experiments, Lab III-5 Extracting, Isolating, and Visualizing DNA; this lab is (to my mind) even more interesting than the AP #3 lab, since it allows you to extract and view DNA yourself.

Be sure to complete and include in your final report any questions including in the lab instructions.

Alternative Lab #2

Goal: To understand DNA sequencing and replication by modeling a sample DNA sequence and performing "replication" on the model.


DNA modeling kits are available from Carolina Biological supply; but you can be as inventive as you like (I always go for edible components when possible; it is a family tradition to consume the evidence). The following is a suggestion, but whatever materials you chose, you will need 6 distinct colors and some kind of connector:


  1. Create a single strand of DNA. Link each white to two reds and one of the bases (orange, green, blue or yellow) with the toothpicks or pretzels. You should make a strand at least 10 white beads (10 red) long.
  2. Create a strand of DNA to match the first, remembering that A and T go together and G and C go together.
  3. Put the strand together with your connectors.
  4. Record your strand as pairs: AT, AT, TA, GC, TA, GC, GC (it doesn't matter what they are, exactly).
  5. Now, decide which is the 5'-3' and which is the 3'-5' side.
  6. Starting at one end, split all the bases apart except for the last one.
  7. On the 5'-3' side, starting at the last remaining joined pair of bases, add the appropriate set of bases, riboses and phosphate equivalents.
  8. For the 3'-5' side, build the entire 8-9 nucleotide strand required to match it, in the 5'-3' direction.
  9. Add the pre-assembled strand to the 3'-5' side.
  10. Break the final pair and examine your two new strands. They should be the same as the original.

Why do you think that assembly always occurs in the 5'-3' direction?


You may wish to take photographs of your models. Identify the sequences you created and map them to an amino acid sequence.

You may consume your model, assuming you made it from edible components.