Answers To Review Questions

1. C. 5' CAGUUCCUAUAAGCUA 3'. Transcription generates RNA (not protein, which is made at the next step, translation, outside the nucleus in eukaryotes). RNA is synthesized in the 5' to 3' direction, and the sequence of the newly synthesized strand is complementary to that of the template DNA strand.

2. E. It is the a factor that binds the promoter sequence and then brings the other subunits onto the DNA.

3. B. The terminator sequence in DNA comprises a GC-rich region followed by a string of adenines. Concerning other answers: (C) stop codons exert their effect during translation, not during transcription. (D) The sequences TTGACA and TATATT, the -35 and -10 boxes, are found in the promoter region of prokaryotic genes, not at the end. (E) Processed eukaryotic RNA terminates with the sequence AAUAAA and a poly-A tail up to 250 nucleotides long, separated by about 20 bases. The presence of uracil should have been enough to tell you that this was not DNA!

4. E. The lac operon is transcribed when lactose is present, generating allolactose, which binds to the repressor, preventing its binding to the promoter, AND if glucose is absent, causing an increase in the cAMP concentration and therefore allowing the cAMP-CAP protein to bind to the lac promoter region.

5. D. The corepressor is tryptophan itself, and the trp operon is only transcribed when tryptophan is absent and therefore needs to be made by the cell. When tryptophan is present at a sufficiently high concentration (viz. A), then it binds to its aporepressor (B, C), which then binds to the promoter, preventing transcription.

6. E. All these processes occur before eukaryotic mRNA is translated at the ribosome.

7. B. RNA polymerase II transcribes protein-coding genes in eukaryotes. DnaB is part of the machinery of DNA replication that assembles, at the appropriate time, at the origin of replication—not at a promoter.

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