Answer to Question 1
No; muscles grow in response to the demands placed on them either through use in daily life/one's occupation or through resistance training. An adequate, balanced diet supports this growth in response to use, but research has not demonstrated an advantage for supplements in addition to diet.
Answer to Question 2
Protein functions as a structural component of muscle, bone, connective tissues, organs, red blood cells, hemoglobin, hair, and fingernails; as enzymes; as a component of hormones; in the maintenance of body tissues; as a carrier to transport substances in body fluids; as an energy source; and in immunity.