The thyroid gland produces thyroxine and
a. growth hormone
b. glucagon
c. norepinephrine
d. androgens
e. calcitonin

The correct answer is E. The thyroid gland produces thyroxine and calcitonin.

Explanation:

Calcitonin is a linear peptide hormone composed of 32 amino acids that are involved in the regulation of calcium and phosphorus metabolism. It was discovered in the thyroid of the pig in 1963.

This hormone is produced in the parafollicular cells of the thyroid gland and its function consists in the reduction of blood calcium levels (Ca2 +), opposing the action of parathyroid hormone.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.