Correct option is C
Explanation-
Ferritin is an iron-storage protein. The 5' UTR of ferritin mRNA contains a stem-loop structure called the Iron Regulatory Element (IRE). Iron Regulatory Binding Proteins (IRBPs) bind to this IRE in iron-deficient conditions. The binding prevents translation by blocking the scanning and unwinding of the stem-loop by initiation factors like eIF4A. When iron is abundant, IRBP doesn't bind (due to conformational changes), allowing normal translation of ferritin.
Statement A - IRBP-IRE interaction prevents eIF4A from resolving the stem-loop structure, thus preventing initiation of translation of ferritin genes - Correct.
IRBP binding at the IRE blocks eIF4A (a helicase in the eIF4F complex) from unwinding the mRNA's stem-loop. This inhibits translation initiation of ferritin when iron is low.
Statement B - IRBP-IRE interaction recruits eIF4A to the 5' UTR, thus promoting translation initiation - Incorrect.
IRBP actually inhibits translation by blocking eIF4A access. It does not recruit eIF4A or promote translation. This is the opposite of what happens.
Statement C - In presence of ferrous ions IRBP is unable to bind the IRE - Correct.
When iron (ferrous ion, Fe²⁺) is present, it binds IRBP, causing a conformational change so it cannot bind the IRE. This allows normal translation of ferritin to proceed, as IRE is free.
Statement D - eIF4A binds directly at the 5' UTR and disrupts the stem-loop structure, thus promoting translation initiation - Incorrect
eIF4A is part of the scanning complex, but its action is indirect and part of the eIF4F complex. It doesn't bind directly to the 5' UTR in the manner described; the key inhibitor here is IRBP, and the focus of the question is on IRBP-IRE, not eIF4A's own binding affinity.
Correct Option is c - (A and C)
These two statements accurately describe the regulatory mechanism of ferritin translation via IRBP-IRE interaction.
