The building of a model of DNA will allow you to better understand the statement " Thestructure of DNA is integral to its function". Although the same chemical substance,DNA, is found is every living cell, you can visualize the many different ways the fournitrogen bases could be sequenced to provide endless variety and diversity. Also, thefunction of DNA is more apparent. The pairing of the nitrogen bases allows the DNAmolecule to replicate and pass on the instructions for heredity with great precision.
27 toothpicks5 side tear strips form continuous feed computer paper2 pieces of 16 gauge wire, each 70 cm longTransparent tapeHot glue gunMarkers: blue, orange, yellow, purple and greenA section of 1 1/2 inch plastic pipe
1. Construction of the deoxyribose/phosphate sides:
a. With a green marker, color the side strips as illustrated on the right. The green squares represent the deoxyribose sugar molecules (deoxyribose C5H10O4 ).
b. The remaining white areas represent the phosphate molecules.
a. With a purple marker, color 15 toothpicks 2/3 of their length. This representsthe double ringed nitrogen base adenine.
b. Use the yellow marker, complement of purple, to color the remaining 1/3 ofthe toothpick to represent thymine. The base pairing of A and T are determinedby the sharing of two hydrogen bonds.
c. Color 12 toothpicks, 2/3 their length, blue, representing guanine. Color theremaining 1/3 length the complement, orange, representing cytosine. The basepairing C and G are determined by the sharing of three hydrogen bonds.
The order of the nitrogen bases is what determines what protein will be coded for.
The DNA molecule, which you will construct, codes for the transcription of aprotein called oxytocin. Oxytocin is a protein that initiates labor and lactation inhumans.
a. It may be necessary to straighten the wire by pulling it through a small hole ina piece of wood.
b. Tape one side of each paper strip for support, this also prevents the strips fromtearing. Pierce a hole in each deoxyribose molecule to allow for insertion of thenitrogen bases (toothpicks).
c. Mark the 5th, 15th and 25th deoxyribose molecule (green square). Tape the wireonto the paper strips. (Not too securely, the wire needs to move slightly whentwisting it later).
Take your strips and wire at this point to the teacher fortwisting. As the wire and strips are wrapped around the plastic pipe, the 5th, 15thand 25th deoxyribose are positioned in a vertical line.
d. You and your partner are now ready to begin inserting the nitrogen bases. Turnone of the side strips 180 degrees (end for end). This will ensure that each end ofthe DNA model as a deoxyribose molecule and a phosphate group. (3' and 5' itemof the grading rubric). Use a piece of masking tape to label the left-hand side ofthe double helix (DNA model). As you proceed, follow the sequence below andinsert the appropriate nitrogen base into the deoxyribose molecule on the left-hand side strip. Insert the other end of the toothpick into the right-hand side strip.
As the toothpicks are positioned one at a time, place a small drop of glue, using a
HOT glue gun, onto the end of the toothpick. Allow the glue to cool (only takes a
moment) to prevent the ends from detaching from the side strips, before going on
to the next nitrogen base. CAUTION: HOT GLUE GUNS ARE HOT. THE
GLUE IS HOT TOO.
e. The base triplets above complete the gene responsible for the coding ofoxytocin. The amino acid sequence for oxytocin is: cysteine, tyrosine, isoleucine,glutamine, asparagine, serine, glycine, leucine, glycine.
Finish the model with any left over nitrogen bases, in any order you wish. Lookthrough the ends of the model and observe the anti-parallelism of the double helixmolecule. (Another item on the grading rubric.)
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