BIOCHEMISTRY - L. Stryer - 1984

VOLUME 3

Part IV INFORMATION

CHAPTER 26. THE GENETIC CODE AND THE RELATIONSHIP BETWEEN GENES AND PROTEINS

QUESTIONS AND PROBLEMS

1. What Amino Acid Sequence is encoded by the following mRNA base sequence? Assume that the reading frame starts from the 5' end: 5'-UUGCCU-AGUGAUUGGAUG-3'.

2. What is The sequence of the polypeptide formed upon The addition of poly(UUAC) to a Cell-free protein-synthesizing system?

3. Single-stranded tobacco mosaic virus RNA was treated with a chemical mutagen. Mutants were obtained in which Proline at a specific position was replaced by Serine or leucine. Subsequent Treatment of the mutant RNA with the same mutagen led to the appearance of phenylalanine at that same position:

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a) What are the putative codons for these four Amino Acids?

b) Which mutagen was likely used: 5-bromouracil, nitrous acid, or an acridine dye?

4. A protein chemist told a molecular geneticist that he had discovered a new mutant Hemoglobin in which aspartate replaces Lysine.

The molecular geneticist was surprised and told his friend to go back and do some more work in the lab.

a) Why did the molecular geneticist express doubt about the plausibility of such an amino acid substitution?

b) What amino acid substitution would have seemed much more acceptable to the molecular geneticist?

5. Below are the Amino acid sequences of a fragment of wild-type and mutant T4 bacteriophage Lysozyme:

a) Could this mutation have arisen via a single base-pair substitution in the T4 phage DNA? If not, how could such a mutant have been generated?

b) What is the mRNA base sequence encoding the Five amino acids in the wild-type protein that differ from the corresponding sequence in the mutant?

6. The RNA transcript of a DNA region from phage G4 contains the sequence 5'-AAAUGAGGA-3'. This fragment encodes three different Proteins. What are their sequences?