A

 actin - One of two proteins involved in muscle contraction (see also myosin). Actin is found in both smooth and striated muscle and also serves as an important structural molecule for the cytoskeletons of many eukaryotic cells. 

 adrenal cortex - this is the outer portion of the adrenal gland; it secretes hormones such as hydrocortisone (a glucocortoid) and aldosterone (a mineralocorticoid). Glucocortoids help cells synthesize glucose, catabolize proteins, mobilize free fatty acids, and inhibit
 inflammation in allergic responses. Mineralocortoids regulate the levels of minerals such as sodium and potassium in the blood. 

 adrenal gland - this gland is found above each kidney, and it made up of an outer wall (cortex) that secretes important steroid hormones and an inner portion (medulla) that produces adrenaline (epinephrine) and noradrenaline (norepinephrine).

 Amino acids - are a class of molecules when combined into very long chains form proteins in living organisms. 

 The twenty common amino acids (alanine, arginine, aspargine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine) all share the same basic chemical
 structure. Each individual amino acid is divided into three groups of atoms: an -NH2 amine group, a -COOH carboxylic acid group, an a variable group called the R-group with composition that differs from amino acid to amino acid. For example, alanine and aspargine, two
 different amino acids, have identical amine and carboxylic acid groups but different R-groups. 

 Amino acids are the most basic unit of proteins, which are vital to cell functioning and produced from amino acids in the process of protein synthesis. 

 Amino acid nomenclature has no specified order to it. Most amino acids were discovered before the chemical system of standardized nomenclature came into use, so amino acids tend to be named based on method of discovery (for example, asparagine from asparagus) or
 other amino acids (phenylalanine as a derivative of alanine). 

 adenosine diphosphate (ADP) - ADP is a molecule which consists of the nitrogenous base adenine linked to the sugar ribose and which has a chain of two phosphate groups attached to the ribose in a linear fashion. ADP is used as an intermediate throughoug
 glycolysis. ATP hydrolyzes to produce ADP and free energy. Image: View the chemical structure

 Adenosine Triphosphate - ATP - is a nucleotide that is the primary source of energy in all living cells because of its function in donating a phosphate group during biochemical activities. ATP is composed of adenosine, ribose, and three phosphate groups and formed by enzymatic reaction from adenosine diphosphate and an orthophosphate. ATP provides energy for every reaction in the body from
 blinking an eye to a 500 pound bench press. It is the single most important molecule in all living things since it serves as the currency for energy in biological systems. Image: View the chemical structure