Sketch the main elements of an inducible operon, such as the lactose operon, and explain the functions
of the operator and promoter regions. What will be an ideal response?
Concepts to Consider: An operon is a set of functionally related structural genes and the DNA
sequences that control them. The operator sequence overlaps part of the promoter region and is
upstream from the structural genes. In the absence of lactose, the lactose repressor binds to this region,
blocking RNA polymerase from binding to the promoter site so that the genes are not transcribed.
When lactose is present, some molecules of lactose are converted into allolactose, which binds to an
allosteric site on the repressor such that it can no longer bind to the operator sequence. This allows the
RNA polymerase to bind to the unblocked promoter region and the structural genes of the operon to be
transcribed. As a result of this control sequence, the gene products of the lactose operon are produced
only when needed.
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What will be an ideal response?
The envelope of the flu virus is made of
a. cellulose b. capsid protein c. phospholipids d. peptidoglycan and capsid protein e. phospholipid and capsid protein