Chapter 15
The genetic code is almost universal. Why do you think it is nearly universal? (Page
282)
Answer: The very strong similarity among organisms indicates a common ancestry of the
code.
It is widely accepted that RNA polymerase has no proofreading capacity. Would you
expect high or low levels of error in transcription as compared with DNA replication?
Why do you think it is more important for DNA polymerase than for RNA polymerase to
proofread? (Page 283)
Answer: One would expect higher amounts of error in transcription over DNA
replication. Proofreading is important in DNA replication because errors in DNA
replication will be passed on to offspring as mutations. However, RNA's have very short
life spans in the cytoplasm therefore mistakes are not permanent. The lack of
proofreading allows for faster transcription.
The prokaryotic promoter has two distinct elements that are not identical. How is this
important to the initiation of transcription? (Page 285)
Answer: The promoter acts a binding site for RNA polymerase. The structure of the
promoter provides information as to both where to bind, but also the direction of
transcription. If the two sites were identical, the polymerase would need some other cue
for the direction of transcription.
How can the same gene encode different transcripts? (Figure 15.11)
Answer: Splicing can produce multiple transcripts from the same gene.
How is the wobble phenomenon related to the number of tRNAs and the degeneracy of the
genetic code? (Figure 15.19)
Answer: Wobble not only explains the number of tRNAs that are observed due to the
increased flexibility in the 5’ position, it also accounts for the degeneracy that is observed
in the Genetic Code. The degenerate base is the one in the wobble position.