Discuss the structure of the DNA molecule and how specific features, such
as the sequence of chemical bases and the rules of base pairing, allow the molecule to carry and pass on information related to the inheritance of traits. Have students build a model of DNA with a given sequence of chemical bases.
Note: To assemble, put the connectors in flat and then rotate 90 degrees to lock into place.
The 3D printed parts were designed in Tinkercad.
DNA provides the instructions for building and operating all living things. The DNA instructions are divided into segments called genes. Each gene provides the information for making a protein, which carries out a specific function in the cell. A molecule of DNA (DeoxyriboNucleic Acid) is composed of two backbones and four types of chemical bases.
The backbone is formed by a chain of alternating phosphates and sugars. Each sugar molecule in the backbone provides an attachment site for one of the chemical bases. The four types of chemical bases are: adenine, thymine, cytosine and guanine. They usually are represented by their first letters: A, T, C and G. The bases form pairs in a very specific way: A always pairs with T, and C always pairs with G. A pair of bases is connected by hydrogen bonds.
Each base in the pair is also connected to a sugar compound in the DNA backbone A DNA molecule is often compared to a ladder, with the two backbones forming the sides of the ladder and the base pairs forming the steps, or rungs. However, instead of a straight ladder, DNA looks like a twisted ladder, known as a double helix (“double” for the two backbones). The DNA sequence is the consecutive order of bases on one side, or strand, of the twisted ladder. The other strand has a complementary sequence determined by the base pairing rules. The specific matching of the base pairs, A with T and C with G, provides a way for exact copies of DNA to be made. This process is called DNA replication.
In DNA replication, the double helix ladder is untwisted and the two strands are separated by breaking the hydrogen bonds between the base pairs. Next, two new strands are made by reading each side of the DNA ladder, one step (base) at a time. At each step, the matching base fills in (with its associated sugar and phosphate) to complete the rung and lengthen the new DNA strand. When the process is complete, there are two identical DNA double helices, each containing one original and one new strand.
DNA replication is an important part of the cell division process. Before a cell divides, it first duplicates its DNA so that the new cell will have the same genetic information. The specific base pair matching during replication ensures that exact DNA copies are made.
- Understand that chromosomes are structures in the nucleus of a cell that carry genes
- Understand that genes are smaller units that contain the hereditary code, DNA
- Students will be able to describe the structure of the DNA molecule.
- Students will be able to explain the rules of base pairing.
- Students will understand that information is stored within the DNA molecule in the form of a sequence of chemical bases, each referred to by the first letter of its name (A, T, C and G).
Content Standard C: Life Science - Reproduction and Heredity; every organism requires a set of instructions for specifying its traits; hereditary information is contained in genes, located in the chromosomes of each cell; a human cell contains many thousands of different genes.
Content Standard C: Life Science - Molecular Basis of Heredity; in all
organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, T, C, and G); the chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular “letters”) and replicated (by a templating mechanism); each DNA molecule in a cell forms a single chromosome.
B. AAAS Benchmarks for Science Literacy
The Living Environment: Heredity - The information passed from parents to offspring is coded in DNA molecules.
When isolated from a cell and stretched out, DNA looks like a twisted ladder. This shape is called a double helix. The sides of the DNA ladder are called the backbone and the steps (also called rungs) of the ladder are pairs of small chemicals called bases. There are four types of chemical bases in DNA: Adenine (A), Cytosine (C), Guanine (G), and Thymine (T).
They form pairs in very specific ways:
Adenine (A) always pairs with Thymine (T)
Cytosine (C) always pairs with Guanine (G).
Discuss the structure of the DNA molecule and how specific features, such as the sequence of chemical bases and the rules of base pairing, allow the molecule to carry and pass on information related to the inheritance of traits.
Have students build a model of DNA with a given sequence of chemical bases.
Begin class with a discussion about DNA. Include in your discussion that DNA contains all of the instructions necessary to build and operate a living organism and that DNA molecules can be found inside the cells of all living things.
Show students a diagram depicting what the DNA molecule looks like as you describe its structural features. Inform students about the four-letter DNA alphabet, A, T, C, and G, and describe the rules of base pairing. Explain that information is stored within the DNA molecule in the form of a sequence of chemical bases represented by these four letters.
Reinforce that the structure of DNA and the rules of base pairing enable the
molecule to perform its function of storing heritable information.
This lesson plan can be enhanced by viewing the documentary Raising the Mammoth (parts 1 and 2), which aired on the Discovery Channel .
Print out multiple sets of Helix Backbones and ATCG connectors
A set consists of:
2 - Helix pieces
5 - Connectors
5 - Each of A, T, C, and G nodules
Students should be able to follow directions to make their DNA models, identify the parts of the model, and participate in the class discussion about DNA.
Three points: students followed directions accurately, completed their model completely
and accurately, identified each part of the model, and actively participated in the class discussion about DNA.
Two points: students followed most of the directions accurately, completed their model
but had a couple of errors, identified most parts of the model, and participated somewhat in the class discussion.
One point: students followed some of the directions accurately but were not able to
complete their model, identified some parts of the model, and participated a little bit in
the class discussion.