Biology Now, 2e

Answers ■ A19

Figure 10.8

Q1: Which amino acid always begins an amino acid chain? Which

codon and anticodon are associated with that amino acid?

A1: Methionine always begins the chain. The associated codon

and anticodon are AUG and UAC, respectively.

Q2: Each of the codons for stopping translation binds to a tRNA

molecule that does not carry an amino acid. How would the binding

of a stop codon cause the completed amino acid chain to be released?

A2: Because there is no amino acid, the growing protein becomes

detached from the mRNA.

Q3: Given the partial mRNA sequence that you specified in Figure

10.6’s question 3 as being transcribed from the DNA template

strand, what is the amino acid sequence that would be translated?

A3: The partial mRNA sequence ACUCUUCUGGUCCCA ACA

yields the amino acid sequence threonine-leucine-leucine-valine-

proline-threonine.

Figure 10.9

Q1: How many codons code for isoleucine? For tryptophan? For

leucine?

A1: Isoleucine: 3. Tryptophan: 1. Leucine: 6.

Q2: What codons are associated with asparagine? With serine?

A2: Asparagine: A AU, A AC. Serine: AGU, AGC.

Q3: From the partial mRNA sequence that you specified in Figure

10.6’s question 3 as being transcribed from the DNA template

strand, remove only the first A. What amino acid sequence would

be translated as a result of this change? How does that sequence

compare to the amino acid sequence you translated from the

original mRNA sequence? Bonus: What kind of mutation is this?

(Hint: See Chapter 9.)

A3: The partial mRNA sequence CUCUUCUGGUCCCA ACA

yields the amino acid sequence leucine-phenylalanine-tryptophan-

serine-glutamine. There is one less amino acid, and each of the

amino acids is different. Bonus: Deletion.

Figure 10.10

Q1: Why is an insertion or a deletion in a gene more likely to alter

the protein product than a substitution, such as A for C, would?

A1: Because an insertion or deletion causes a “frameshift,” so

every single amino acid from that point on is likely to be different,

as opposed to a substitution, where, at most, one amino acid

changes.

Q2: Which would you expect to have more impact on an organism:

a point mutation as shown here, or the insertion or deletion of a

whole chromosome (discussed in Chapter 8)?

A2: The loss or addition of an entire chromosome, with all the

genes on it, is likely to have far more impact on an organism than a

mutation within a single gene.

Q3: Which mechanisms in a cell prevent mutations? (Hint: Refer

back to Chapter 6 if needed.)

A3: Checkpoints in the cell cycle prevent (or at least repair)

mutations.

Figure 10.11

Q1: As illustrated here, at what control point is transcription

regulated?

A1: Control point 2.

Q2: What is a possible advantage of regulating gene expression

before transcription, versus after?

A2: The cell does not waste time and energy producing mRNA

transcripts that it will not use.

Q3: If you wanted to up-regulate production of the hemagglutinin

protein in a tobacco plant carrying the hemagglutinin gene,

at which control point(s) would that be possible? Justify your

reasoning.

A3: Control points 1–4 all could have an impact on the amount

of hemagglutinin being produced by a cell. The levels of DNA

compaction, transcription, mRNA degradation, and translation

all work together to increase or decrease the production of

hemagglutinin. Modifying any one of these or any in combination

can have a large impact on production.

CHAPTER 11

END-OF-CHAPTER ANSWERS

1. c


2. b


3. c


4. biogeography: 4, fossil record: 1, DNA sequence similarity: 2,
   embryonic similarity: 5, homologous traits: 3


5. d


6. b


7. adaptation, natural selection


8. In artificial selection, humans choose which organisms
   survive and reproduce. In natural selection, the environment
   determines which organisms survive and reproduce, by
   selecting for individuals with more beneficial inherited traits
   and against individuals with less useful ones.


9. d


10. species Y


11. d


12. All (or most) of the current continents.

ANSWERS TO FIGURE QUESTIONS

Figure 11.3

Q1: What is selective breeding, and how does it work?

A1: Selective breeding is the process by which humans allow

only individuals with certain inherited characteristics to breed.

Generation after generation, the selective breeder chooses which

individuals mate and pass their traits to offspring.