In the form of proteins, amino acids comprise the second-largest component (water is the largest) of human muscles, cells and other tissues. Outside proteins, amino acids perform critical roles in processes such as neurotransmitter transport and biosynthesis.n biochemistry, amino acids having both the amine and the carboxylic acid groups attached to the first (alpha-) carbon atom have particular importance.
Ad lib redirects here. For other uses, see Ad lib (disambiguation). Ad libitum (/Ã¦dËlÉªbáµ»tÉm/) is Latin for at one's pleasure; it is often shortened to ad lib (as an adjective or adverb) or ad-lib (as a verb or noun).
Definition of up for Students. 1  1 : in or to a high or higher place or position She put her hand up. 2  2 : in or into a vertical position Stand up. 3  3 : from beneath a surface (as ground or water) Come up for air.  4 : with greater force or to a greater level Speak 1  up. 5 : so as to make more active Stir up the fire.