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Mechanism of Thyroxine Action

View the animation below, then complete the quiz to test your knowledge of the concept.






1Which of the following statements about thyroxine is TRUE?
A)it is water-insoluble
B)it is lipophilic
C)it cannot pass through the cell membrane
D)A and B
E)A, B and C



2The thyroid gland secretes
A)large amounts of triiodothyronine but no tetraiodothyronine.
B)large amounts of tetraiodothyronine but no triiodothyronine.
C)large amounts of both triiodothyronine and tetraiodothyronine.
D)large amounts of triiodothyronine and small amounts of tetraiodothyronine.
E)large amounts of tetraiodothyronine and small amounts of triiodothyronine.



3Which of the following statements about thyroxine is TRUE?
A)Both the T3 and T4 forms enter target cells.
B)Inside the target cell, all T3 is converted to T4.
C)Only the T4 form can enter the nucleus.
D)A and B
E)A, B and C



4Thyroxine is brought to target cells via a protein-carrier.
A)True
B)False



5The thyroxine-hormone receptor complex increases the level of transcription of specific genes.
A)True
B)False







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