1. Attenuation is a regulatory mechanism that has been wellstudied in the E. coli trp operon, involved in tryptophanbiosynthesis. Which of the following accurately describesattenuation?
A: The goal of attenuation is to suppress the expression ofbiosynthetic enzymes when the end product of the pathway isavailable.
B: The attenuator is a stem loop structure at the 5´ end of themRNA transcript that resembles the structure of thefactor-independent termination sequence.
C: When tryptophan levels are low, the trp operon transcript isattenuated before the operon's structural genes aretranscribed.
D: Attenuation allows fine-tuning of the levels of mRNA transcriptfrom the trp operon in response to small changes in theavailability of tryptophan.
E: The trpL mRNA contains a \"stall\" sequence for the ribosome thatincludes two adjacent trp codons.

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2. Which of the following are true statements concerning thesimilarities and differences between prokaryotic and eukaryotic DNAreplication:
A: Prokaryotes use DNA polymerase III as the primary replicativeenzyme, whereas eukaryotes use DNA polymerase I.
B: Most prokaryotes replicate a single chromosome from a singleorigin of replication, whereas eukaryotes have thousands of originsof replication spread over multiple chromosomes.
C: In eukaryotes, DNA replication is continuous, whereasprokaryotes replicate their DNA discontinuously in a process thatgenerates Okazaki fragments.
D: Eukaryotic DNA replication is more complex than prokaryoticreplication, because eukaryotes must dissociate and replicatechromatin as part of the process.
E: A homodimer of DNA polymerase III catalyzes the replication ofboth leading and lagging strands in prokaryotes, whereas twodifferent DNA polymerases are required to replicate the leading andlagging strands in eukaryotes.

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3. Ammonia is toxic and must be converted to urea in order to beexcreted. The following statements describe the process:
A: ammonia is transported into the liver as either alanine orglutamine.
B: transamination is a key step in the release of ammonia fromglutamine.
C: urea is formed and excreted primarily by the kidneys.
D: alanine carries ammonia waste from muscle to the liver; once inthe liver, alanine is converted via pyruvate to glucose, which maybe returned to the muscle.
E: carbamoyl phosphate is a key intermediate in the conversion ofammonia to urea.
F: urea is ultimately formed by hydrolysis from ornithine