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-
They cannot synthesize functional beta-galactosidase
They cannot transport lactose from the medium into the cell
The lac operon is constitutively active in these cells
In the presence of glucose, E. coli cells do not utilize lactose
the lac operon in E. coli contains three structural genes: z, y, and a . The z gene specifically codes for the enzyme beta-galactosidase (\beta -gal), which is responsible for the hydrolysis of lactose into its monomeric units, galactose and glucose . The bacteria utilize these monomers as a source of energy . If the z gene is mutated, the cell cannot synthesize functional beta-galactosidase, rendering it unable to break down lactose . Consequently, in a medium where lactose is the only available energy source, the bacteria will fail to grow . Mastering these operon mechanics is a high-priority strategy, as NCERT textbooks provide the foundation for approximately 95% of NEET Biology questions .
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