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CHAPTER 15
Concept check questions (in figure legends)
FIGURE 15.1
Concept check: Which disease occurs when homogentisic acid oxidase is defective?
Answer: Alkaptonuria occurs when homogentisic acid oxidase is defective.
FIGURE 15.2
Concept check: What is the enzymatic function that is missing in the strain 2 mutants?
Answer: The strain 2 mutants are unable to convert O-acetylhomoserine into
cystathionine.
FIGURE 15.3
Concept check: Describe the role of DNA in the synthesis of a polypeptide.
Answer: The role of DNA is to store the information that specifies the amino acid
sequence of a polypeptide. It is a storage role.
FIGURE 15.5
Concept check: Which two amino acids do you think are the least soluble in water?
Answer: Tryptophan and phenylalanine are the least soluble in water.
FIGURE 15.7
Concept check: What type of bonding is responsible for the formation of the two types
of secondary structures?
Answer: Hydrogen bonding promotes the formation of secondary structures in proteins.
FIGURE 15.9
Concept check: Explain how the use of radiolabeled amino acids in this procedure
helped to reveal the genetic code.
Answer: Only one radiolabeled amino acid was found in each sample. If radioactivity
was trapped on the filter, this meant that the codon triplet specified that particular amino
acid.
FIGURE 15.10
Concept check: What are the two key functional sites of a tRNA molecule?
Answer: A tRNA has an antiocodon that recognizes a codon in the mRNA. It also has a
3’ acceptor site where the correct amino acid is attached.
FIGURE 15.12
Concept check: What is the difference between a charged tRNA versus an uncharged
tRNA?
Answer: A charged tRNA has an amino acid attached to it.
FIGURE 15.13
Concept check: How do the wobble rules affect the total number of different tRNAs that
are needed to carry out translation?
Answer: The wobble rules allow for a smaller population of tRNAs to recognize all of
the possible mRNA codons.
FIGURE 15.15
Concept check: Explain how mRNA plays a role in all three stages.
Answer: A site in mRNA promotes the binding of the mRNA to the ribosome. The
codons are needed during elongation to specify the polypeptide sequence. The stop codon
is needed to terminate transcription.
FIGURE 15.17
Concept check: Why does a bacterial mRNA bind specifically to the small ribosomal
subunit?
Answer: The Shine-Dalgarno sequence in mRNA is complementary to a region in the
16S rRNA within the small ribosomal subunit. These complementary sequences
hydrogen bond with each other.
FIGURE 15.18
Concept check: What is the role of peptidyl transferase during the elongation stage?
Answer: Peptidyl transferase catalyzes the peptide bond formation between amino acids
in the growing polypeptide chain.
FIGURE 15.19
Concept check: Explain why release factors are called “molecular mimics”.
Answer: The structures of release factors, which are proteins, resemble the structures of
tRNAs.