Using a DNA Sequence:
Teacher Information

(Download the MS Word version of this document.)

Background Information

See Student Worksheet.

Materials

• Autoradiogram showing a portion of the Angiotensin II receptor gene sequence (1 per student)
• Genetic code chart

Procedure

Use the DNA sequence for DNA replication and protein synthesis.

1. Use the simulated autoradiogram to determine the sequence of DNA belonging to a portion of the Angiotensin II receptor. Notice that the autoradiogram has been divided into four columns. The first column represents all guanine nucleotides. The second column represents all adenine nucleotides, the third is all thymine nucleotides, and the last column shows all cytosine nucleotides.
2. Working from the bottom of the autoradiogram, place a ruler under the first nucleotide seen on the autoradiogram. This area is marked with *. Notice how it is the only nucleotide going across all four columns. Record this nucleotide as the first nucleotide found in the gene sequence.
3. Move the ruler up 1 nucleotide. Notice how it is the only nucleotide found going across all four columns. Record this nucleotide as the second nucleotide in the gene sequence.
4. Continue reading the autoradiogram until you have reached the top.
5. With your sequence, complement to form the other strand of DNA.
6. Use this sequence of DNA to have students practice DNA replication.
7. Next, introduce the concepts involved in protein synthesis- an understanding that DNA codes for mRNA, and mRNA carries information for making proteins.
8. Using the DNA strand made from the autoradiogram, have students transcribe the DNA strand into a mRNA strand.
9. Compare mRNA strands produced by the class but do not make any corrections to the strand.
10. Determine the amino acid sequence by using a genetic code chart.
11. Compare amino acid sequences of the Angiotensin II receptor.
12. Discuss how an addition/deletion and a substitution of 1 nucleotide on the DNA sequence affects the protein being made.

Analysis and Conclusions

• The DNA, mRNA, and amino acid sequence read from the autoradiogram is as follows:
  • DNA: AAT GTG GCG GTA TAG AGG AAC AGG ATG GTG TCG TGT TCC AAA TTC ACT
  • MRNA: UUA CAC CGC CAU AUC UCC UUG UCC UAC CAC AGC ACA AGG UUU AAG UGA
  • Amino acid: Leu His Arg His Iso Ser Leu Ser Tyr His Ser Thr Arg Phe Lys
• Students would complement the DNA sequence to show a complete DNA strand. The process of DNA replication can be illustrated with the newly synthesized strand being a different color so that students see that only half of each DNA molecule made is new.
• DNA replicates for cells to undergo cell division.
• 15 amino acids are found in the sequence. Leucine, arginine, serine have different codons for the same amino acid. Leucine codons are UUA and UUG. Arginine codons are CGC and AGG. Serine codons are UCC and AGC.
• tRNA picks up and carries an amino acid to the ribosome where the corresponding mRNA codon is found.
• If amino acid sequences do not correspond to the key, students may have read the sequence incorrectly from the autoradiogram or could have complemented mRNA incorrectly to DNA.
• If the first U on the mRNA is deleted, the amino acid sequence would be: tyrosine, threonine, alanine, isoleucine, serine, proline, cysteine, proline, threonine, threonine, alanine, glutamine, glycine, leucine, serine.
• Deleting 1 nucleotide adjusts the reading frame of the codons, therefore, the possibility of new amino acids being coded for increases.
• Depending on where the substitution is placed, either a change in the amino acid sequence will occur or it will not.