b) Four different E. coli strains (1-4) with mutations affecting lac gene expres

Question

b) Four different E. coli strains (1-4) with mutations affecting lac gene expression were grown in medium without glucose but with or without lactose and had the phenotypes shown in the table below. Complete the table to indicate if genes in the lac operon would be transcribed (switched ON) or not transcribed (4 marks) (switched OFF) with or without lactose in mutants 1-4. Without With lactose lac genes lac genes ON or OFF ON or OFF OFF Mutant Mutant phenotype number lactose: wild type 1 Repressor cannot bind to operator 2 Repressor cannot bind allolactose 3 lacl repressor gene is not transcribed 4 lacZ gene has a missense mutation ON Page 9 of 13

Explanation / Answer

2. Repressor cannot bind allolactose OFF ON

3. lacI repressor gene is not transcribed OFF ON

4. lacZ gene gas a missense mutation OFF ON

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