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The characteristics of dna and the use of the model of dna structure in classrooms

Ask students to brainstorm traits they have that are passed on from their parents, such as eye color, hair texture, and facial characteristics. Then ask them how these traits are passed on from one generation to the next. The answer is DNA, or deoxyribonucleic acid. Explain that all organisms carry an elaborate blueprint containing the information necessary to develop and maintain life. This "manual of instructions" is located in a chemical molecule called DNA.

DNA is found within a person's genes. Genes are small structures found in chromosomes, structures within the nucleus of cells. Tell students that DNA works something like the alphabet. While the alphabet has 26 letters, DNA's "alphabet" has only four letters.

These letters are guanine Gadenine Acytosine Cand thymine T. Just as the 26 letters of the alphabet can be used to form millions of words for communication, DNA's alphabet can be combined to form codes with more than five billion combinations of G's, A's, T's, and C's.

The differences in these combinations result in differences among human beings. The DNA molecule consists of two strands that form a double helix, a spiraling shape much like a twisted ladder. The DNA molecule has a sugar component, a phosphate component, and four different bases—adenine, thymine, cytosine, and guanine. To help students understand how these components fit together to form DNA, have each student make a model of DNA with fishing line, dried pasta, and different-colored pipe cleaners.

First, give each student 2 pieces of line, 18 pieces of pinwheel pasta, 16 pieces of ziti pasta, and different-colored chenille stems pipe cleaners. Explain that the pinwheel pasta represents the sugar component, the ziti pasta the phosphate, and the chenille stems each of the bases. Tell students to start with the pinwheel pasta and alternate with the ziti pasta as they thread the pasta on the line.

On each line, they should string nine pieces of pinwheel pasta alternating with eight pieces of ziti.

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Wrap the line around the final piece of pasta at the end of each line so that the pasta does not fall off. After pasta has been strung on both lines, each line should have a total of 17 alternating pieces of pasta. Have students lay the two lines side by side. Then give students the "code" for the chenille stems—the blue stem represents adenine; the green stem, thymine; the purple stem, cytosine; and the orange stem, guanine.

DNA Structure

Explain that the bases in DNA are found in pairs and that adenine always pairs with thymine and cytosine always pairs with guanine. Have students represent these base pairs with twisted chenille stems. First, have them twist the eight blue stems and eight green stems together, making a total of eight blue-green stems, about 2 inches long.

Likewise, have them twist the eight purple and eight orange stems together, making a total of eight purple-orange stems, about 2 inches long. Students will find that the chenille stems twist together easily. Now, have students create a "ladder" using the pasta lines as the sides and the twisted chenille stems as steps.

Beginning at the top, students should connect the two ends of a twisted chenille stem to the top pasta pieces on the two lines. Then use a second chenille stem to connect the next two pasta pieces directly across from each other.

They should continue building their ladder, one step at a time, until they have connected the bottom two pieces of pasta. Remind them that they can place the twisted chenille stems in any order. The blue-green stems do not have to alternate with the orange-purple stems. After all the stems have been woven, the DNA model is complete. Using the DNA models, discuss the following questions with the class.

To enhance the discussion, you may want students to look up additional information in other resources. How do the bases pair up in a DNA molecule?

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How does your model help you figure this out? What differentiates one DNA molecule from another? How do you think a DNA molecule makes an exact copy of itself? How does its structure help it do so? Assign the Take-Home Activity Sheet: Then go over the vocabulary words to make sure that students have mastered them.

Adaptations Have older students use this topic to integrate art and science. Instruct them to design and create a DNA model using materials of their own choice.

Suggested materials include stained glass, clay, beads, buttons, wood pieces, recycled materials, and food items. They should include a key that explains what each item represents.

After students have completed their models, have them display the models in the classroom.