Mini Quiz 4: Lac operon

What is meant by an operon in DNA?

• A collection of genes that perform the same function

• A functioning unit of DNA containing a cluster of genes controlled by a single regulatory signal or promoter

• A region on DNA which can affect the whole organism

• A process where genes in an organism can affect other genes

The lac operon is found in ___ and the proteins produced are involved in metabolism of ____.

• human colon cells ; glucose

• fungi ; galactose

• plants ; starch

• bacteria ; lactose

In the presence of lactose, the lac operon will be switched ​ (a)   , ​ (b)   of structural genes will be transcribed and the ​ (c)   will be produced.

• on
• mRNA
• enzymes
• DNA
• off
• tRNA
• promoter
• RNA polymerase
• operator
• repressor

Reorder the following

• No transcription of structural genes occur, no enzymes are produced.

• lacI gene is transcribed and translated into repressor protein.

• RNA polymerase is unable to bind to promoter.

• In the absence of lactose, repressor protein binds to operator.

Which of the following statements are FALSE?

• In the presence of lactose, lac operon is switched on.

• Lactose will convert into allolactose before binding to repressor.

• Enzymes beta-galactosidase, permease & transacetylase are not produced in the presence of lactose.

• In the presence of lactose, RNA polymerase can bind to promoter of lac operon.

What happens to the lac operon if the lacI gene is mutated?

• Repressor protein may be non-functional.

• Structural genes cannot be transcribed.

• RNA polymerase cannot bind to promoter.

• It does not affect the lac operon.