BIOLOGY I/MEZZETTI A Design Your Own DNA Molecule de nin MA STANDARD 3.1: Describe the basic structure (double helix, sugar/phosphate backbone, linked by e complementary nucleotide pairs) of DNA (A) – LEARNING OBJECTIVES: ___ 1. Explain the principal function of DNA. ___ 2. Describe the structure of DNA. ___ __ BACKGROUND: Th  DNA = Deoxyribonucleic Acid ym  DNA is made of nucleotides ine  Nucleotides contain a base (A, T, G, or C) + deoxyribose sugar + phosphate (T) The 4 different bases form base pairs: - Adenine binds with Thymine ___ Guanine binds with Cytosine ___  The shape of DNA is a double helix with a right-handed spiral turn (like a twisted ladder) ___ with the steps representing the base pairs and the sugar+phosphate backbone as the hand ___ rails. In our model, the colored chenille stems represent the phosphate (P) groups and the __ white portion that wraps around the colored stems represents the sugar groups (S) (see diagram below). Guanine (G) – PRE-LAB: Complete 10-1 Worksheet ______Materials (per pair): Cytosine Important: Pick 2 pipe cleaners of two different colors; pick 4 different colors of beads. Put (C) – the color of the pipe cleaners and beads in the chart below before you start. Then as you go ______place the colors on the lines that correspond to the parts of the DNA molecule. _____  2 ______12” pipe cleaners  2 ______12” pipe cleaners  12 ______6mm beads (A)  12 ______6mm beads (G)  6 ______6mm beads (T)  6 ______6mm beads (C)  scissors  ruler Procedures: 1. Cut each ______pipe cleaner into six 2 inch sections. 2. The pony beads represent the 4 different bases: 3. Because A and G molecules have 2 rings, you will use 2 beads for each of these molecules. Use one bead for T and C molecules, which have only one ring. 4. Thread beads representing an Adenine and Thymine base pair onto one of the 2-inch ______pipe cleaner. (Remember to use 2 beads for A and one bead for T). Prepare 6 of these segments. 5. Prepare 6 Guanine and Cytosine base pairs, using 2 ______beads for G and 1 ______bead for C.

6. Connect one ______pipe cleaner segment to the ______pipe cleaner approx. 1 cm

from the top. Wrap the end of the ______pipe cleaner around the colored pipe cleaner. Connect the other end to the second colored pipe cleaner (see photo). This is where you can be creative with the genetic code - you can choose to make your own DNA sequence! 7. Follow the same procedure for the remaining yellow segments and beads. Add each consecutive base pair (______pipe cleaner segment) approximately 1 cm from the previous base pair. 8. When all 12 base pair segments have been added to the DNA molecule, you should have a molecule that looks like a ladder. 9. To make your double helix, twist your model slightly so the molecule forms a spiral. DNA molecules have a right-handed helix shape that winds in one direction (see diagram on next page). You can figure out the direction by sliding the fingers of your right hand along backbone. If it is right-handed, your thumb should be moving forward while you do this. 10. CONGRATULATIONS! You have created your own unique DNA molecule. The sequence of the base pairs in the DNA ladder is what makes different DNA molecules unique, and is what the Human Genome Project and other genome sequencing projects are all about. Compare your DNA molecule with other DNA molecules. How are they similar? How are they different? 11. Extension: Create a model of RNA using a ______beads for uracil.

DNA model with a right-handed helix Figure from Access Excellence (www.accessexcellence.org Modified from:

http://www.life.uiuc.edu/hughes/footlocker/