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6.2: Using Gene Expression DNA Codes for Proteins – Student Edition (Human Biology)

Difficulty Level: At Grade Created by: CK-12

Draw students' attention to the key ideas by using posters or overhead transparencies.

Emphasize that DNA has two primary functions: replication for cell division and providing the coded information in genes for the production of specific proteins.

Introduce protein synthesis by having students complete Mini Activity: Run to the Ribosome. For the DNA role, use cards with a different color on each side: one color to represent the DNA code and the other color to represent the messenger RNA code.

Follow up with Activity 5-1: Making Protein.

Select appropriate Projects if time permits.

At the end of the section refocus students' attention on the key ideas.

Run to the Ribosome The following activity is an excellent activity to use in preparing students for Activity 5-1. This activity is strongly recommended. We placed it here, rather than in the student edition, due to the need for teacher involvement in getting students started.

  1. Locate the space where this activity will take place. Use a string, chalk, or tape to represent the cell membrane. Mark off a smaller circle inside the larger cell membrane to represent the nucleus (for example, a circle 3 meters in diameter). Place a chair inside the cytoplasm to represent the ribosome.
  2. Select 1 person to represent DNA, 1 person to represent mRNA, and 5 students to represent tRNA. The rest of the students represent amino acids.
  3. In order for the DNA to specify the production of a protein, the DNA selects 3-letter codes. DNA writes each code on a \begin{align*}5” \times 7”\end{align*} card.
  4. Each tRNA selects one of the 3-letter codes held by DNA and records the complementary triplet on a \begin{align*}5” \times 7”\end{align*} card. For example, if the 3-letter code is GUA, the complementary triplet would be CAU.
  5. The amino acids each make a name tag and write one of the 5 codes recorded by tRNA. Have all amino acids and tRNA assemble in the cytoplasm.
  6. DNA stacks the cards in a sequence. Now the race begins. DNA gives mRNA the code sequence (stack of cards). The mRNA leaves the nucleus taking the code (stack of cards) to the ribosome (chair) in the cytoplasm and places the cards on the floor in the sequence determined by DNA.
  7. Each of the 5 tRNAs finds an amino acid having the same code on their name tag. The tRNAs take their amino acid to the ribosome. Each tRNA has the amino acid stand on the appropriate card. The tRNA leaves the ribosome.
  8. The amino acids hold hands forming a protein (polypeptide chain). The completed protein leaves the ribosome.

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