Reading the DNA Code Using the APH DNA Twist Model

By Laura Hospitál on Feb 03, 2017

Students make their own keys describing the tactile and color surfaces of the nitrogen bases of the model (as shown in the picture on the right). Students who will not benefit from the information about the color may only describe the tactile surface.
Students use these keys to "read" the DNA molecule and to "write" the appropriate code for the corresponding strand of DNA (using base-pairing rules). Finally students will complete a short worksheet in which one strand of the DNA is given and the corresponding strand must be determined.  If students are not yet familiar with DNA base-pairing rules, these should be taught prior to this actiivty. 


  • DNA - deoxyribonucleic acid- molecule found in all living things that holds the code for inherited characteristics
  • double helix - the spiral staircase structure of the DNA molecule
  • nucleotide - in a nucleic acid chain, a subunit composed of a sugar, a phosphate, and a nitrogenous base
  • base pairing rules - the rules stating that thymine bonds with adenine and guanine bonds with cytosine in DNA



Making the Key 

See key attached as a guide.

As students enter the room have the DNA Twist model ready for each student. 

  1. Tell students that they will make a key to use for today's activity of the DNA model to help them "read" the DNA molecule
  2. Have students make a key with the following information: (See picture)
    • Guanine - blue, bumpy
    • Cytosine - yellow, smooth 
    • Adenine -  white, sandy
    • Thymine - brown, banded

Using the Key 

  1. After students have made the key, explain that DNA is read up and down rather than left to right like English. Explain that if we could cut the molecule down the middle, we would be reading the bases on one side.
  2. Guide students to "read" the nitrogen bases from bottom to top on the right hand side of the molecule and to write down this list of bases. 
  3. Students will use the base-pairing rules - A=T and G=C to write out a complementary strand to the right hand strand. 
  4. Students can check their work by using the left hand side of the DNA molecule as a guide.
  5. Now that students have practiced writing out a complementary strand of DNA using the base-pairing rules, if time allows, have them practice using the attached worksheet


Younger students and more modified high school classes may not complete the DNA Base-Pairing Activity after the initial introduction. 

NGSS Standards:

Middle School - Growth, Development and Reproduction of Organisms

LS3.A: Inheritance of Traits
  • Genes are located in the chromosomes of cells, with each chromosome pair containing two variants of each of many distinct genes. Each distinct gene chiefly controls the production of specific proteins, which in turn affects the traits of the individual. Changes (mutations) to genes can result in changes to proteins, which can affect the structures and functions of the organism and thereby change traits. (MS-LS3-1)

High School : Structure and Function 

LS1.A: Structure and Function
  • Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1)
  • All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. (HS-LS1-1) 

High School - Inheritance and Variation of Traits

LS3.A: Inheritance of Traits 
  • Each chromosome consists of a single very long DNA molecule, and each gene on the chromosome is a particular segment of that DNA. The instructions for forming species’ characteristics are carried in DNA. All cells in an organism have the same genetic content, but the genes used (expressed) by the cell may be regulated in different ways.  Not all DNA codes for a protein; some segments of DNA are involved in regulatory or structural functions, and some have no as-yet known function. (HS-LS3-1)

Collage of DNA twist model


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