In a typical regulation of gene transcription in bacteria, the expression of gen
ID: 262405 • Letter: I
Question
In a typical regulation of gene transcription in bacteria, the expression of gene Y is under the control of protein X. Protein X cannot bind to the gene Y’s promoter unless a specific signal (Sx) converts X into an activated form (X*). Upon binding to the promoter, X* activates the transcription of gene Y.
1) Consider a slightly more complicated regulation network (illustrated in the diagram below) where both activated forms proteins X and Y (X* and Y*) are needed to activate the expression of gene Z AND X* is needed to activate the expression of gene Y. Signal Sx and Sy trigger the conversion of X and Y into X* and Y* respectively. Gene activation can only occur when the activators (X* or/and Y*) reaches a specific threshold of concentration.
a) Assume that gene X is under the control of a constitutive promoter and the input signal Sy is already present. Describe how the expressions of protein Y and Z change over time when the input signal Sx is introduced. Be as specific as possible.
b) A mutation in gene Y increases the concentration threshold at which Y* activates the transcription of gene Z. What would be the consequence of this mutation on the expression of protein Z over time? Briefly explain.
2) When Sx has been present for an hour, the amount of Z and Y have reached steady state (rate of production and degradation are equal). On the following diagram draw carefully the change in amount of protein Y and Z when the input signal Sx is suddenly removed (Z and Y degradation occurs at identical rate). Make sure to respect the timescale. Assume that the deactivation of X* is immediate when Sx is removed. Briefly explain.
3) Imagine that Y is a repressor of gene Z (repression occurs when Y* reach its repression threshold) while the rest of the regulation network shown in part 1) remains the same. Describe the change (if any) of the expression of proteins Y and Z when the input signal Sx is introduced (assume that Sy is already present).
Steps Binding of X* to gene Y's promoter Transcription & translation of gene Y ~1millisecond 1 second 5 minutesExplanation / Answer
Ans-1-A Before the introduction of Sx all the three genes will be non functional as Sx is the first activator of the reaction so as we introduce Sx in the reaction it will activate gene X and only then the reaction will start and the expression of gene Y and Z will occur. So before introduction of Sx there will be no expression , expression will only be possible after the introduction of Sx.
Ans-1-B This type of mutation will lead to the delay in the expression time of the gene Z as a large amount of Y* will be required to express the gene Z. More concentration means more time so it will lead to delay as compared to normal concentration of gene Y*.
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