Lac Operon

Q. In the lac operon of E.coli, which of the following happens when the repressor binds to the operator?

1. Transcription occurs
2. Transcription is blocked
3. RNA polymerase binds to the promoter
4. Transcription is slowed down

Q. Lac operon is the system used by E.coli to

1. Make lactose
2. Breakdown lactose
3. Breakdown lactic acid
4. Both A and B

Q. Lactose operon of Escherichia coli is _______________

1. Monocistronic
2. Inducible
3. Repressible
4. Both B and C

Q. E.coli cells with a mutated Z gene of the lac operon cannot grow in a medium containing only lactose as the source of energy because

1. They cannot synthesise β-galactosidase.
2. The acetyl group from acetyl CoA cannot be transferred to lactose.
3. Lactose cannot be transported from the medium into the cell.
4. The lac operon cannot function at all without this gene.

Q. ‘Lac’ in lac operon refers to

1. Lactic acid
2. Lactose
3. Levulose
4. Lactobacillus

Q. Regarding the assertion and reason, select the correct answer.
Assertion [A]: Lac operon of E.coli is a type of ‘inducible’ operon.
Reason [R]: Lac operon normally remains ‘switched off’, and functions only when the host (whose gut harbours the E.coli) consumes milk.

1. Both A and R are true and R explains A
2. A is true and R is false
3. Both A and R are true, but R does not explain A
4. Both A and R are false

Q. Which of the following represents the correct sequence of genes of a lac operon system?

1. Promoter gene, repressor, structural genes
2. Repressor, structural genes, operator gene
3. Promoter gene, operator gene, structural genes
4. Structural genes, promoter gene, operator gene

Q. Considering lac operon, match the following:

$\begin{array}{cc}ColumnI& ColumnII\\ p.Regulatorgene& i.Bindingsiteforrepressorprotein\\ q.Operatorgene& ii.Code\left(s\right)fortheproteinoftheenzymes\\ r.Promotergene& iii.Code\left(s\right)forrepressorprotein\\ s.Structuralgenes& iv.BindingSiteforRNApolymerase\end{array}$

1. p-ii, q-i, r-iii, s-iv
2. p-iii, q-i, r-iv, s-ii
3. p-iii, q-iv, r-i, s-ii
4. P-iv, q-i, r-ii, s-iii

Q. The Operon regulates the gene expression at what level?

1. Inhibiting transcription of mRNA
2. Inhibiting enzymes
3. Inhibiting passage of mRNA
4. Inhibiting substrate-enzyme reaction

Q. Identify the mismatched pair(s) of the genes related to the lac operon and the respective proteins they code for.

1. LacY- β-galactosidase
2. LacA- β-galactoside transacetylase
3. LacZ- lactose permease
4. All are correct