Answers to the To Review and To Think About questions are necessarily brief. In many cases more detailed answers can be gleaned from the text itself. In many cases, too, other answers are possible. For visual comfort in reading these answers, a space has been placed between nucleic acid triplets.
1. Definitions in text.
2. See Table 16.1.
3. DNA replication and transcription take place in the nucleus. Translation takes place in the cytoplasm.
4. See Table 16.2.
5. Possible answers include: editing, multiple functions, transcription factors, and feedback loops. In addition, genes are used over and over and product parts are continuously recycled.
6a. AAU GUG AAC GAA CUC UCA A
b. UGA ACC CGA UAC GAG UAA U
c. CCU UAU GCA GAU CGA UCG U
7a. CGA TAG TCT GTA TTT TCT CCT
b. CAC CGC ATA TGT TTT GGC CCA TCC
c. TCC TTT TGG GGA GAA TAA TAT CTA
8. Refer back to the appropriate diagrams.
9. Answers will vary. Check Table 16.4.
10. Answers will vary. Use Table 16.4 and go backwards.
11. Answers will vary.
12a. CGT TTT GGC GCT AAT AGT TCG AAG
b. CGU UUU GGC GCU AAU AGU UCG AAG
c. arg-phe-gly-ala-asn-ser-ser-lys
d. mRNA code:
CGU GUU UUU UUU UUG UGG GGC GCG CGC GCU
CUA UAA AAU AUA UAG AGU GUU UUC UCG
CGA GAA AAG AG G
arg-val-phe-phe-leu-try-gly-ala-arg-ala-
leu-STOP-asn-ilu-STOP-ser-val-phe-ser-
arg-glu-lys------
e. asparagine becomes lysine
13a. Since purine always pairs with pyrimidine, structural integrity remains constant.
b. A pairs with T, C with G, T with A, G with C.
c. A pairs with U, C with G, U with A, C with G.
d. Begin with methionine
e. Same constant pairing.
f. Pairing is constant.
14. Editing.
15. A defect in protein folding can cause an enzyme not to catalyze a reaction properly, a carrier molecule (such as hemoglobin) not to carry a substance (such as oxygen) properly, or a structural molecule not to form a proper structure. Other answers are possible.
16a. Valine replaced by leucine.
b. Valine replaced by leucine.
c. Shifts to codon to CAG, glutamine -- frame shift continues right on down the row.
d. Adds histidine as 5th amino acid
e. Frameshift to isoleucine at the beginning -- frameshift continues right on down the row.
17. UUC GCU AAA GAC UGU
TO THINK ABOUT
1. The genetic code is the same. Everyone has his or her own unique set of nucleotides (and therefore DNA bases).
2. Most amino acids are coded for by more than one sequence of DNA bases; therefore a mutation might not change the amino acid. In the second case, an amino acid might be changed, but that amino acid might be a part of an edited out portion of the sequence. It would not appear in the final product.
3. Different functions; different needs.
4. Simple math. Two-nucleotide codons could encode a maximum of 16 amino acids. The three-nucleotide codons actually encode a maximum of 64 amino acids. We only have 20 in regular use.
5. Histidine is coded for by CAU or CAC. Arginine has six codes. CGU and CGC would require only replacing the A with a G.
6. Enzyme production, feedback loops, or other similar answers.
7a. Wrong polypeptide.
b. Protein not produced.
c. Protein not produced -- stall.
d. Protein not produced -- stall.
e. Incorrect translation.
8a-c. Answers will vary.
9. Answers will vary.
10. Insertion, frameshift, changing of STOP codon. Other answers also possible.
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