When DNA is undergoing RNA transcription a small portion of the double-stranded DNA unzips, allowing the transcription enzymes access to the nucleotides. RNA only forms on one of the DNA strands and always begins at the codon, or three-nucleotide “word,” TAC. As the RNA is created, it unzips from DNA and floats free. A RNA/DNA model will appear to have a bubble at its center with a partially attached RNA strand.
The Building Blocks
Divide the foam balls into three piles: 60 for the sugar backbone, 30 for RNA transcription section and 40 for the standard DNA strands.
Designate a color for each nucleotide and the backbone sugar. For example, adenosine (A) is orange, thymine (T) is yellow, guanine (G) is green, cytosine (C) is blue, uracil (U) is pink and the sugar is purple.
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Paint the balls from the RNA transcription pile according to the following pattern: 6 as T, 9 as A, 3 as U, 6 as C and 6 as G.
Paint the standard DNA nucleotide balls to represent 10 each of A, T, G and C.
Use white toothpicks to create base pairings of the balls in step 4, connecting A to T and C to G.
Add an additional toothpick across from the central toothpick on either side of the base pair.
Paint the sugar foam balls their designated color.
Create Sugar Backbone Strands
Insert a red toothpick into a sugar foam ball.
Attach another sugar foam ball to the end of the toothpick.
Insert a toothpick perpendicular to the first toothpick.
Repeat steps 1 through 3 until you have eight separate strands, four with 10 sugar balls and four with five sugar balls.
Create the RNA Transcription Portion of the Model
Lay two of the five-sugar chains on the work surface so that the sugars at one end of the strand are touching, forming a 45-degree angle.
Connect the two touching sugars with a red toothpick.
Repeat steps 2 and 3 for the other two strands.
Lay the other angular strand so that the point faces left and attach the nucleotides to the inside of the angle according to the following pattern: (top) TACGGCTATA (bottom).
Lay the other angular strand so that the point faces right and attach the nucleotides to the inside of the angle according to the following pattern: (top) ATGCCGATAT (bottom).
Create the RNA chain with the remaining balls from step 3 according to the following pattern: (top) AUGCCGAUAU (bottom). Connect the chain by placing a white toothpick at a 90-degree angle to the toothpick inserted in step 4.
Lay the RNA chain next to the DNA strand created in step 4.
Connect the five base pairs at the bottom of the RNA strand to the five base pairs at the bottom of the DNA strand using white toothpicks.
Leave the top portion of the RNA strand free.
Finishing the Model
Lay two of the 10-sugar chains parallel to each other on your work surface.
Connect the two chains by pressing the outer toothpicks of a base pair created in step 5 of the “Building Blocks” section into adjacent sugars on the chain, continuing until you have attached 10 base pairs.
Repeat steps 1 and 2 for the two remaining 10-sugar chains.
Lay the RNA portion of the model and the other angular DNA strand side by side with the points facing outward.
Lay one of the double-stranded, 10-sugar DNA strands below the RNA portion and the other above the RNA portion.
Connect the sugar backbones together using red toothpicks.
Place one toothpick a sugar at the bottom end of the RNA/DNA model.
Lay the foam block next to the toothpick end of the model and press the toothpicks into the block.
Hold the model at both ends and lift the model upright.