Which stop codon has been found to encode selenocysteine?
Answer: C
Correct answer: UGA
UGA is normally a stop codon, but in a particular structural context - a stem-loop called the SECIS element in the mRNA - it is read instead as selenocysteine, the twenty-first amino acid. A dedicated tRNA and elongation factor are needed, and the mechanism shows that the code is not quite as fixed as it looks.
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Which of the following defines an open reading frame (ORF)?
Answer: D
Correct answer: A possible gene predicted by DNA sequencing
An open reading frame is a stretch of sequence running from a start codon to a stop codon with no stop in between - long enough that its occurrence by chance is improbable. Finding one in a newly sequenced genome is evidence of a probable gene, which is how most genes in a sequenced genome are first identified.
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Puromycin halts translation because it structurally resembles ________.
Answer: C
Correct answer: an aminoacyl-tRNA
Puromycin mimics the aminoacyl end of a charged tRNA, so the ribosome transfers the growing chain onto it. The resulting peptidyl-puromycin cannot be translocated and falls off, releasing an incomplete polypeptide.
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__________ states that only valid data will be written to the database.
Answer: A
Correct answer: Consistency
Consistency requires that a transaction take the database from one valid state to another, preserving every integrity constraint - keys, referential integrity, and application rules such as an account balance never going negative. A transaction that would violate one is aborted.
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The Oracle RDBMS uses the ____ statement to declare a new transaction start and its properties.
Answer: B
Correct answer: SET TRANSACTION
Oracle uses SET TRANSACTION to begin a transaction explicitly and set its properties - read-only or read-write, and the isolation level. Oracle needs no BEGIN: a transaction starts implicitly with the first DML statement, and SET TRANSACTION is used when the properties must be declared. BEGIN TRANSACTION is the SQL Server form.
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Which phage always carries a small piece of E.coli genome?
Answer: B
Correct answer: Mu
Phage Mu is a transposon as well as a virus: it integrates at random sites in the host chromosome, and when it excises it carries away a short piece of adjacent E. coli DNA. That is why every Mu particle contains a little host genome - and why Mu is such a useful tool for making insertion mutations.
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Negative regulation of protein synthesis is accomplished by
Answer: C
Correct answer: the binding of a repressor to the DNA
Negative regulation works by preventing transcription: a repressor protein binds the operator, a stretch of DNA beside the promoter, and physically blocks RNA polymerase from moving on. Removing the repressor - as lactose does with the lac repressor - is what turns the gene on.
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The genetic code is described as degenerate because ________.
Answer: D
Correct answer: most amino acids are specified by more than one codon
Degeneracy means 61 sense codons encode only 20 amino acids, so most amino acids have several synonymous codons. Crucially the code is not ambiguous: a given codon always specifies the same amino acid.
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Transaction processing is associated with everything below except
Answer: C
Correct answer: Confirming an action or triggering a response
Transaction processing records business activity, maintains the data and produces reports from it. Confirming an action or triggering a response belongs to a real-time or decision support system rather than to transaction processing as such - which is concerned with capturing and storing what happened.
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Which of the following is not a transaction state?
Answer: D
Correct answer: Compensated
The states of a transaction are active, partially committed, failed, aborted and committed. There is no “compensated” state - a compensating transaction is a separate transaction run afterwards, not a state of the original.
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