13.  a. and b. 5′ UUG GGA AGC 3′

c. and d. With the assumption that the reading frame starts at the first base,

NH₃ – Leu – Gly – Ser – COOH

For the bottom strand, the mRNA is 5′ GCU UCC CAA 3′ and, with the assumption that the reading frame starts at the first base, the corresponding amino acid chain is

NH₃ – Ala – Ser – Gln – COOH

17.  There are three codons for isoleucine: 5′ AUU 3′, 5′ AUC 3′, and 5′ AUA 3′. Possible anticodons are 3′ UAA 5′ (complementary), 3′ UAG 5′ (complementary), and 3′ UAI 5′ (wobble). Although complementary, 5′ UAU 3′ also would base-pair with 5′ AUG 3′ (methionine) owing to wobble and therefore would not be an acceptable alternative.

22.  Quaternary structure is due to the interactions of subunits of a protein. In this example, the enzyme activity being studied may be that of a protein consisting of two different subunits. The polypeptides of the subunits are encoded by separate and unlinked genes.

26.  No. The enzyme may require posttranslational modification to be active. Mutations in the enzymes required for these modifications would not map to the isocitrate lyase gene.

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29.  With the assumption that all three mutations of gene P are nonsense mutations, three different possible stop codons (amber, ochre, or opal) might be the cause. A suppressor mutation would be specific to one type of nonsense codon. For example, amber suppressors would suppress amber mutants but not opal or ochre.

33.  Single amino acid changes can result in changes in protein folding, protein targeting, or post-translational modifications. Any of these changes could give the results indicated.

41.  If the anticodon on a tRNA molecule was altered by mutation to be four bases long, with the fourth base on the 5′ side of the anticodon, it would suppress the insertion. Alterations in the ribosome also can induce frameshifting.

42.  f, d, j, e, c, i, b, h, a, g.