Question

Ferritin coding Transferrin coding 222 in -AAAAA-3 5 -AAAAA-3 IRES IRES FER TFR FER TFR FER TFR FER TFR Low iron High iron Low iron Western blot Northern blot Set 1 Set 2 Set 3 Set 4 (fig52) The top of the figure above shows the mRNAs for both Ferritin (FER) and the Transferrin Receptor (TFR), showing the locations of the iron response element stem-loops (IREs). Below the mRNA diagrams are sets of northern and western blots for FER/TFR that correspond with the scenarios below. Match the northern/western blot set to the scenario. FER and TFR mRNAs are normal, as diagrammed above. TER IRES (AU rich), replaced with FER IRE sequences (FER mRNA remains normal). [Choose] [Choose] Set 2 Set 1 Set 4 none of the above Set 3 [Choose] < FER 5'UTR replaced with TER 5'UTR (TER mRNA remains normal). < IREBP no longer inactive with high iron concentration. [Choose]

Answer 1

First option is going to set 3 because Western blot of of this set shows low irons have no ferritin protein but high irons have .and low iron have transferrin receptor protein and high iron level don't have transferrin .it is because in low iron, cytosolic aconitase (iron regulatory proteins) binds to the 5 'utr regions and translation is blocked .but when iron concentration is high, aconitase binds with iron and don't sit on 5'utr region and blocking of translation is withdrawn .

In case of transferrin , 3'UTR have iron responsive elements(IRE) .

This ire is bound by aconitase similarly but when aconitase is bound the mRNA of transferrin remain stable because it protect from nuclease digestion of 3'mrna. And if iron high, aconitase release and the protection is also withdrawn and thus mRNA become digested .

Now, if you see Northern blot, whether low or high concentration of iron is , ferritin mrna is present because ferritin translation is affected by iron level not the stability of its mRNA.

But transferrin mRNA stability is related with iron level that why when iron is higher , no mRNA of transferrin is present because then mRNA of transferrin will be digested by nuclease.

Set 2 goes with scenario 4 because then, ferritin mrna will be as it's level is not related with free iron concentration.

mRNA of transferrin will also be present in both cases because , in higher iron concentration, aconitase will not be released and thus mRNA will be protected.

In case of protein level, transferrin will be present in both cases because translation of transferrin is not related with iron level(it's translation is controlled because it's mrna stability is controlled by iron level).

But, in case of ferritin, ferritin mrna is translated when iron level is higher because then aconitase is released but,in this case inactivation of aconitase is inhibited so it will be always bound to the 5' UTR of ferritin mrna and thus translation of this will be always blocked.

Scenario 3 is indicated by set 4 because if TFR 5'utr is placed in place of FER 5'UTR, THEN, THIS UTR WILL NOT BIND THE ACONITASE AND THUS FER MRNA WILL ALWAYS BE TRANSCRIBED AND THUS FER PROTEIN WILL ALWAYS BE EXPRESSED.

BUT, TRANSFERRIN MRNA WILL BE PRESENT IN LOW IRON CONCENTRATION BECAUSE OF PROTECTION BUT IN HIGHER IRON CONCENTRATION, ACONITASE WILL BE WITHDRAWN AND MRNA STABILITY WILL BE LOST AND THUS ,IN HIGHER CONCENTRATION OF IRON, TRANSFERRIN PROTEIN WILL. ALSO BE ABSENT.

SCENARIO 2 goes with NOTHING because ferritin mrna is normal so, its mRNA will be present and not dependent on iron concentration.

And it will be expressed when iron level is high, as it is on the northern and western blot data. This data is right .

But if you see , the transferrin mRNA in northern blot, you can see that transferrin mRNA as well as protein is always expressed .

This can only be possible if IRE REGION OF TRANSFERRIN IS ALWAYS BOUND WITH ACONITASE WHICH WILL PROTECT MRNA.

BUT THIS IS NOT POSSIBLE IF IRE OF FERRITIN IS REPLACED IN PLACE OF and even it bind ACONITASE then also , in higher level of iron aconitase will be detached and mRNA and thus protein will not be present.

Even, if the replaced ire don't bind the ACONITASE then, TRANSFERRIN mRNA and protein will not be present whether iron concentration is low or higher because mRNA will be digested.

But in set 1 , TFR IS EXPRESSED IN BOTH CASES.

THANK YOU