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The lactose present in the growth medium of bacteria is transported to the cell by the action of:
z = β-galactosidase (hydrolysis), y = permease (membrane permeability/entry), a = transacetylase (acetyl transfer). Permease allows entry!
The lac operon consists of three structural genes: z, y, and a. Each encodes a specific polypeptide essential for lactose metabolism in E. coli.
The z gene codes for beta-galactosidase, which cleaves lactose into galactose and glucose. The y gene codes for permease, a transmembrane protein that increases cell permeability to beta-galactosides, allowing lactose uptake. The a gene encodes a transacetylase.
Transport of lactose across the bacterial cell membrane into the cytoplasm is strictly mediated by lactose permease.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Permease increases membrane permeability to beta-galactosides, enabling lactose uptake into E. coli.
RNA polymerase carries out transcription; DNA polymerase carries out replication.
Beta-galactosidase hydrolyzes lactose into glucose and galactose intracellularly.
Transacetylase transfers an acetyl group from acetyl-CoA to beta-galactosides.
Selecting beta-galactosidase because it is the most well-known enzyme of the lac operon.
"The y gene codes for permease, which increases permeability of the cell to beta-galactosides. A very low level of expression of lac operon has to be present in the cell all the time, otherwise lactose cannot enter the cells."
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