Question

(2 pts) You are studying lactose metabolism and have been culturing E. coliin different medias. One media has only glucose, one has only lactose, and a third has both glucose and lactose.

(1 pt)You notice that some of the cultures grown in the presence of both glucose and lactose are metabolizing lactose. Which type(s) of mutation(s) could cause this to occur?

(1 pt)You notice that some E. colicultures failed to grow in the presence of only lactose. You know that normal E. coliare able to metabolize lactose so something must be wrong. Which mutation(s) could explain this?

(2 pts) Why is it advantageous for organisms to be able to regulate their gene expression? Please explain in 1-3 sentences.

     

(4 pts)You are studying how a certain species of grass decomposes in a semi-arid grassland in southern Arizona to get an idea on the C dynamics of the region. You find that after a few months the grass litter you’ve been sampling has a higher abundance of fungi than earlier samplings coupled with a decreased abundance of bacteria. You compare the chemical composition of the earlier litter samplings with the older litter and you find that this species of grass has a high concentration of cellulose and the cell solubles (sugars like glucose) have declined rapidly over the experiment.

(2 pts)You know that cellulase expression in microbial decomposers is contingent on Carbon Catabolite Repressor (CCR) which is a cellulose sensor and works the same as the lacrepressor in E. coli. Would CCR be bound to the operator on the older litter? Please explain why in 1-3 sentences.

Answer 1

1: Mutation in operator and /or regulator gene could make the bacteria to metabolize lactose even in presence of glucose in medium. Mutation in operator gene would not allow binding of repressor protein to it, leading to constitutive expression of lac operone. Mutation in regulatory gene could lead to absence of repressor protein or presence of non functional repressor protein that can no longer bind to operator region to inhibit the expression of lac operon in presence of glucose in medium.
So, operator constitutive mutation and repressor mutation are responsible for use of lactose sugar even in presence of glucose.

2: Super repressor mutation (repressor protein mutation) does not allow binding of lactose (inducer) to repressor protein. It leads to inability of bacteria to turn on expression of lac operon in presence of lactose only.
3: It is advantageous to regulate gene expression to not to waste the cellular energy in expression of genes when the respective enzymes/proteins are not needed by cells.