V. Materials. To be procured by each student: Genetic code VI. Procedure 1. Assume that a segment of a protein-coding gene has been sequenced and one strand (strand A) of that segment is shown below. The component nitrogenous bases are designated by capital letters corresponding to the first letter of their names. 5'-TTCTTGTCATACTGCTGGCTGCCCCACCAGCGAATGGTGACAAACAAG-3' Determine the sequence of nitrogenous bases in the complementary strand (strand B) and indicate both strands (A & B) as Figure 3.1. Label the two strands and their respective 5' and 3' ends. 2. Suppose that the two strands (A & B) have separated to serve as templates for DNA replication. Suppose further that each DNA strand is replicated starting from a 3- nucleotide RNA primer that is complementary to one end of the strand. a. To which end (5' or 3') of the A strand would the primer attach and what would be the primer's sequence? b. To which end (5' or 3') of the B strand would the primer attach and what would be the primer's sequence? Write separately the A and B strands on the space provided for Figure 3.2. Label their 5' and 3' ends and then, show the RNA primer sequence attached to one end of each strand. Also label the 5' and 3' ends of each RNA primer. Use an arrow to indicate the direction of DNA synthesis in each strand. 3. Assume that strand B is part of the transcribed strand of the gene. If strand B is transcribed, what would be the corresponding sequence of nitrogenous bases in the RNA transcript? Abbreviate the names of the bases as before (use U for uracil) and indicate the sequence as Figure 3.3. Label the 5' and 3' ends. 4. Assume that the segment of the gene under consideration is part of an exon; that is, the whole segment is translated. If the first three bases in the transcript constitute one codon, how many codons in all are there in the transcript? Indicate the codons in the second column of Table 3.1. Start with the codon at the 5' end of the transcript. In the third column, indicate the anticodons that can recognize each codon considering the wobble of the genetic code. In the fourth column, indicate the ammo acid. corresponding to each codon if the RNA transcript is translated. 5. Suppose that the segment of the gene considered above contains an intron; that is, its RNA transcript has a portion bordered by the consensus splicing signal sequences: GU at the 5' end of the intron and AG at the 3' end. If so, how long is the intron? Write out the sequence of that intron as Figure 3.4. Label its 5' and 3' ends. 6. Answer the study questions. 2