Which of the following is not true of the lac operon?
A. Transcription produces a single polycistronic mRNA containing the lacZ, lacY, and lacA genes.
B. The lacI gene is controlled from the same promoter as the lacZ gene.
C. The Lac repressor protein is constitutively expressed.
D. The operator region regulates transcription through interaction with the Lac repressor protein.
Which of the following steps occurs third during yeast Ty element transposition?
A. packaging of RNA in a VLP along with reverse transcriptase, a protease, and integrase
B. transport of Ty RNA into the cytoplasm where it is translated into VLP proteins
C. transcription of Ty element in the nucleus
D. infection of nucleus with VLP
E. Conversion of mRNA into double-stranded DNA with reverse transcriptase
Which of the following is not true of repairing double-strand breaks by recombination?
A. After invasion of the homologous chromosome, the 3' end of the invading strand acts as a primer for DNA synthesis.
B. The broken ends are processed, with the 3'-ending strand selectively degraded to create 5' overhangs.
C. The 3' single strand extensions invade the homologous chromosome, displacing the homologous strand and base pairing with the complementary strand.
D. As a result of the two strand invasions, the two homologues are linked at two places and are called a branched intermediate.
E. The enzymes required for strand invasion belong to a class of proteins called recombinases.
Exceptions to the genetic code have been identified. Which one of the following is a known exception?
A. A codon might not always encode the same amino acid.
B. A single stop codon, UGG, may be the only stop codon recognized.
C. Alanine codons instead of methionine codons may be used for the initiation of translation.
D. The codons in mitochondria are reversed (e.g., instead of AUG, the methionine codon in mitochondria is GUA).
Which of the following suggested a method of DNA replication to Watson and Crick?
A. The backbone of the DNA helix is antiparallel.
B. Due to complementary basepairing, each strand could act as a template for the other.
C. The DNA helix has a major and a minor groove.
D. The two strands are held together by strong, covalent bonds.
E. The DNA helix is stabilized by hydrophobic stacking.
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