Final Review

What is the function of reverse transcriptase?

• To synthesize RNA from DNA

• To synthesize DNA from RNA

• To synthesize proteins from genes

• To break phosphodiester bonds

A bacteria has a mutation that causes the lacY gene to be defective, meaning that galactose permease is inactive. What effect(s) will this have on the bacteria?

• Lactose will overaccumulate in the cell, so gene expression will be constitutive

• Lactose will not be imported into the cell, so gene expression will be constitutive

• Lactose will be imported into the cell, but it cannot be broken down

• Lactose will not be imported into the cell, so transcription will not be induced.

Put the steps of transcription initiation (for bacteria) in the correct order:

• RNAP opens the DNA helix, sigma binds to the promoter, sigma is released.

• Sigma binds to the promoter, sigma is released, RNAP opens the DNA helix

• Sigma binds to the promoter, RNAP opens the DNA helix, sigma is released

• RNAP opens the DNA helix, sigma is released, sigma binds to the promoter

Does transcription begin downstream or upstream of the -35 box in prokaryotes?

• Downstream

• Upstream

Answer explanation

Sigma binds to the -10 and -35 box, so the proceeding transcription must occur downstream (to the right of the operon)

As an undergraduate researcher in the lab, you are attempting to produce protein by utilizing bacterial E. Coli cells. In order to express your protein, a repressor on the lac operon must be removed. Your two options to induce expression are IPTG or lactose. IPTG is almost identical in structure to lactose, but it cannot be broken down by B-galactosidase. Which would be better to use?

• IPTG because it cannot be broken down by B-galactosidase and its concentration will therefore remain constant

• Lactose because IPTG cannot bind to the repressor on the lac operon

• IPTG because it cannot be broken down by B-galactosidase and its concentration will therefore increase overtime

• Lactose because it is most similar in structure to glucose, which provides energy for the cell

A scientist wants to genetically modify a mushroom to resist browning by using CRISPR. When he designs his experiment, however, he adds the wrong base pair to the single guide RNA (sgRNA). What will be the greatest issue with this design flaw?

• The sgRNA will not be able to bind to the tracrRNA

• The Cas9 enzyme will lose its endonuclease ability

• The DNA cannot be repaired after cleaving

• The Cas9 enzyme will not be able to locate the sequence of interest

 Under what conditions is expression greatest in bacterial cells?

• High lactose, low glucose, high cAMP

• Low lactose, high glucose, high cAMP

• High lactose, low glucose, low cAMP

• Low lactose, high glucose, low cAMP

How do you stop transcription of the trp operon in a bacteria?

• Nothing- the default state of the trp operon is 'off'

• Trp (co-repressor) must bind to the repressor

• Lactose must bind to the repressor

• Asp must bind to the operon

A bacteria has a lac operon in which the lacI and lacY gene is mutated. This leads to the inactivation of B-galactosidase (from lacY) and no repressor being synthesized (from lacI). What does this mean?

• Transcription will occur constitutively

• Transcription cannot occur as there will be no lactose in the cell

• Transcription will occur, but only when glucose is imported into the cell

• Transcription cannot occur as there is no repressor

Which of the following is FALSE?

• The trp operon leads to the synthesis of tryptophan, and the lac operon allows for lactose to be metabolized

• The trp operon is the negative control of an anabolic pathway, the lac operon is the negative control of a catabolic pathway

• Lactose induces expression of the lac operon

• The lac operon needs a co-repressor for the repressor to be activated