DNA and Protein Synthesis

Exercise 1: Modeling DNA

The students must attach the DNA model to this lab report.

Note which nucleotides form pairs—cytosine and guanine, and adenine and thymine form pairs.

Questions

A. The following list indicates the bases on one strand of a DNA molecule. Write in the names of the bases that could pair with each to make the complementary strand.

B. What are the three components of a DNA nucleotide? How do these molecules connect together?

C. What are the four bases found in DNA? Which of these bases pair together?

( Ex p e ri m e n t ) ( DN A an d P rotei n S y n t h e sis )

( ww w . H O L s c i e n c e . c o m ) ( 148 ) ( © H a nds-On L a bs, I n c . )

Exercise 2: The Globin Gene

Procedure

1. Complete the DNA molecule by writing a complementary strand.

Coding Strand: CGT CTC TTC GGA CAC Complementary Strand:

2. Write the mRNA sequence that will be created in the process of transcription. The DNA coding strand has the information for the gene, so the strand must be transcribed. The relationships are slightly different for RNA, because RNA does not have T; therefore, U should be substituted for T. To transcribe DNA to RNA, the pairing relationship is A – U, T – A, C – G, and G – C, respectively.

Coding Strand: CGT CTC TTC GGA CAC

mRNA Strand:

3. Translate the mRNA into amino acids. Use Table 1 as a reference. Remember, when a “stop”

codon is recognized, the protein creation is terminated.

mRNA Strand:

Amino Acids Formed:

Questions

A. How many nucleotides would it take to construct the mRNA coding strand of the β-subunit of the hemoglobin A molecule?

B. How many nucleotides would it take to model the entire β-subunit of the hemoglobin A

molecule?

C. Is the β-subunit of the hemoglobin A molecule a complete DNA molecule (chromosome) or part of one? Explain.

D. What would happen if one of the DNA nucleotides was deleted? What if the first T was substituted for an A? Would a substitution always result in a change? Explain why or why not.

E. Using your newly formed model of DNA from Exercise 1, write the coding strand below. Use the coding strand to determine the mRNA strand and the amino acids formed. Do this separately for Row 1 and Row 2 of your DNA model.

F. Did the new DNA model form any two of the same amino acids?

G. Optional: Compare the amino acids that were formed in this experiment with those of classmates who also performed this experiment. Were there many similarities?