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Key Ideas

  • The genetic information contained in cells is stored in DNA molecules and copied accurately so that each daughter cell receives the same information.
  • The genetic code is represented by sequences of triplet nucleotides in the DNA molecules.
  • Different cell types in your body use or express different portions of your DNA called genes. Genes code for the production of specific proteins in the cell.
  • The transcription of mRNA and its translation at the ribosomes are the processes involved in making proteins.


Students learn about DNA and the information it stores in the genetic code. They explore the physical structure of DNA. Then they learn how it is replicated by building and manipulating a model of a DNA double helix. Students also isolate DNA from thymus tissue to observe its texture and study other physical properties of the molecule. They investigate the process by which the mRNA code is transcribed from the DNA code for a gene, and then how mRNA is translated into protein at the ribosomes.



\checkmark describe the composition and structure of DNA.

\checkmark demonstrate how DNA replicates.

\checkmark explain the roles of DNA, mRNA, tRNA, and amino acids in making protein.

\checkmark describe how the genetic code is expressed in different cells.


amino acids, codon, DNA polymerases, double helix, genes, helicase, messenger ribonucleic acid (mRNA), nucleotides, replication, RNA polymerase, transcription, transfer RNA (tRNA)

Student Materials

Activity 4-1: Removing DNA from Thymus Cells

  • Activity Report
  • Safety goggles
  • Sample of fresh thymus cells in a beaker; Sand; Liquid soap, clear, in a beaker with an eyedropper; Water in a beaker with an eyedropper; Alcohol; Cheesecloth square (several layers, 15 \times 15 \ cm); Mortar and pestle; Test tube; Small funnel; Test tube rack; Wooden skewer; Forceps; Eyedropper; Permanent marking pen; Paper towels; Black construction paper, 4 \times 4 \ cm; Transparent tape; Microscope, slides, and cover slips

Activity 4-2: Building and Using a DNA Model

  • Resource
  • Activity Report
  • Scissors; Paper; 6 different sets of colored paper; Tape

Teacher Materials

Activity 4-1: Removing DNA from Thymus Cells

  • Activity Report Answer Key
  • Serrated knife for cutting the thymus tissue
  • Extra student materials, especially cheesecloth, skewers, test tubes, and fresh thymus cells

You can substitute glass for the stirring rod.

Methylene blue stain can be used to stain the thymus nuclei in Step 5.

Optional: DNA visuals, including models and/or posters

Model of a cell with a large, distinct nucleus

Picture of a human torso to show the location of the thymus gland

Activity 4-2: Building and Using a DNA Model

  • Activity Report Answer Key
  • Models and diagrams of DNA molecules and nucleotides

Advance Preparation

See Activities 4-1 and 4-2 in the Student Edition.

Activity 4-1: Removing DNA from Thymus Cells

  • Purchase fresh thymus tissue, also called sweetbreads, from your local butcher. You can freeze the thymus tissue if you do not plan to use it right away.
  • Cut the thymus tissue into 2 cm cubes using a clean knife.
  • Keep all solutions cold prior to activity.

Activity 4-2: Building and Using a DNA Model

  • You can have students color the sugars, phosphates, and nitrogen bases as follows. Or you can copy them on the indicated colors of paper.
  • 60 deoxyribose sugars (white)
  • 60 phosphates (orange)
  • 15 of each of the four nitrogenous bases:
    • adenine (red), thymine (blue), cytosine (yellow), and guanine (green)
  • Allow ample time to pre-cut the template pieces.

Interdisciplinary Connections

Math Relate the repeating patterns of triplet nucleotides in DNA to other mathematical patterns.

Social Studies Investigate and write about the history and uses of the Morse code.

Language Arts Write a narrative describing the “synthesis of a protein.”

Enrichment Activity

Enrichment 4-1: Making Protein

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