Question

Describe the effect of chloramphenicol on induction.

If chloramphenicol is added at the same time as lactose, how would this affect the induction of B-galactosidase by lactose?

Answer 1

Chloramphenicol was discovered after being isolated from Streptomyces venezuelae in 1947. Its chemical structure was identified and it was first artificially made in 1949, making it the first antibiotic to be made instead of extracted from a micro-organism.

Chloramphenicol is a nonionized, highly lipophilic compound. It enters bacterial cells by passive or facilitated diffusion and binds primarily to the 50S ribosomal subunit but may also bind to the 30S subunit. As a result bacterial protein synthesis is inhibited.Chloramphenicol can also bind to the mammalian ribosome (70S) that resembles bacterial ribosomes and interfere with mitochondrial protein synthesis. This is particularly relevant in erythropoietic cells.

In E. coli, the enzyme B-galactosidase is an important catalyst in the breakdown of the 12 carbon sugar lactose into two 6 carbon sugars, glucose and galactose. The breakdown of lactose provides an important source of energy for the bacteria.The antibiotic chloramphenicol prevent translation of the message encoded in the m-RNA of B-galactosidase . Chloramphenicol prevents m-RNA from attaching to the ribosomes. Once chloramphenicol is added to the bacterial culture no additional B-galactosidase will be produced, but any already present will continue to function normally.