Question

Most amines are ________, meaning they dissolve in water and therefore cannot cross the cell membrane. The ________ hormones are an exception because they are ________ and can easily cross the cell membrane.

Answer 1

Answer: 1. Lipophobic

              2.Thyroid

              3.lipophilic

Explanation:

 Chemical messengers can be classified by their chemical characteristics including their solubility in water and their chemical structure.  

Depending on their solubility in water they can be classified in two groups:

• Hydrophobic (lipophilic) - Molecules are lipid soluble and can easily cross the plasma membrane.

• Hydrophilic (lipophobic) - Molecules that are water soluble and do not readily cross the plasma membrane.

Depending on the chemical structure  

Amino Acids are lipophobic.

Amines are derived from amino acids and contain an amine group (-NH2, known as the amino group). An important group of these are the catecholamines which contain a 6 carbon ring (catechol) and are derived from tyrosine. These include dopamine, norepinephrine and epinephrine. The thyroid hormone is derived from tyrosine.  All except thyroid hormones are hydrophilic. The thyroid hormone is lipophilic (hidrophobic)