Question

In a haploid eucaryotic organism, you are studying to enzymes that perform sequential conversions of nutrient A supplied in the medium: A-(E1)-> B-(E2)-->C. Treatment of cells with mutagen produces 3 different mutq types with respect to these functions. Mutants of Type 1 show no E1 function; allType 1 mustations map to a single locus on likage group 2. Mutatior of Type 2 show no E2 function; all type 2 mutations map to a single locus on linkage group VIII. Mutations of Tye 3 show no E1 or E2 funcion; all tyoe 3 mutants map to a single locus on linkage group 1

A. compare this system with the lac operon of E.coli pointing out the similarities and defferences.

B. If you were to intesify the mutant hunt, would you expect to find an functionmutant types? explain.

C. why does it appear that the Operon Concept as we understanf it to function in bacteria is not applicable in higher organisms.

Answer 1

a.) Comparison between the given system and lac operon of E.coli -

Similarities :

1. The initial stages of lactose metabolism in E. Coli is similar to the given system. The lac operon consisted of three structural genes out of which lacZ encodes beta galactosidase and lacA encodes beta galactosidase trans-acetylase. LacA can be compared to E1 and LacZ to E2 in the pathway of lactose metabolism.

2. LacA and LacZ act sequentially, one after the other just like E1 and E2.

Differences:

1. Unlike E1 and E2, LacA and LacZ are transcribed under the same promoter and are present at the same locus. E1 and E2 are present on different chromosomes since they are in different complementation groups.

2. Unlike E1 and E2, LacA and LacZ form a single polycistronic mRNA and are translated together.

b.) Yes, if the mutant hunt is intensified, we might obtain mutants from parallel pathways leading to the formation of C. We might also obtain certain mutants which might bypass the given pathway and for C even when E1 or E2 are not functional.

C.) In bacteria, the genes are organised in clusters, transcribed as a single polycistronic mRNA and then co-transported to form dufferedi peptides. But such gene organisation is not found in eukaryotes where the genes contain introns and exons and each gene is under the regulation of a different regulatory region. For example a mutation in the regulatory gene of lac operon would disrupt the function of all the enzymes coded by its structural genes. But such a aituasitudoes not generally arise in eukaryotes due to the difference in gene organisation. Hence, the cincecoof an operon does not apply to eukaryotic organisms.