 Like other biological macromolecules such as polysaccharides and nucleic acids , proteins are essential parts of organisms and participate in virtually every process within cells . Many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism . Proteins also have structural or mechanical functions , such as actin and myosin in muscle and the proteins in the cytoskeleton , which form a system of scaffolding that maintains cell shape . Other proteins are important in cell signaling , immune responses , cell adhesion , and the cell cycle . In animals , proteins are needed in the diet to provide the essential amino acids that cannot be synthesized . Digestion breaks the proteins down for use in the metabolism . 
 Like other biological macromolecules such as polysaccharides and nucleic acids , proteins <a href='drop_aux' title='1'><mark>are</mark></a>essential parts of organisms and participate in virtually every process within cells . Many proteins <a href='drop_aux' title='2'><mark>are</mark></a>enzymes <a href='null_relcl' title='3'><mark>that</mark></a>catalyse biochemical reactions and <a href='drop_aux' title='4'><mark>are</mark></a>vital to metabolism . Proteins also <a href='got' title='5'><mark>have</mark></a> structural or mechanical functions , such as actin and myosin in muscle and the proteins in the cytoskeleton , which form a system of scaffolding <a href='null_relcl' title='6'><mark>that</mark></a><a href='uninflect' title='7'><mark>maintains</mark></a> cell shape . Other proteins <a href='drop_aux' title='8'><mark>are</mark></a>important in cell signaling , immune responses , cell adhesion , and the cell cycle . In animals , proteins are needed in the diet to provide the essential amino acids <a href='null_relcl' title='9'><mark>that</mark></a>cannot be synthesized . Digestion <a href='uninflect' title='10'><mark>breaks</mark></a> the proteins down for use in the metabolism . 
Like other biological macromolecules such as polysaccharides and nucleic acids , proteins essential parts of organisms and participate in virtually every process within cells . Many proteins enzymes catalyse biochemical reactions and vital to metabolism . Proteins also got structural or mechanical functions , such as actin and myosin in muscle and the proteins in the cytoskeleton , which form a system of scaffolding maintain cell shape . Other proteins important in cell signaling , immune responses , cell adhesion , and da cell cycle . In animals , proteins r needed in the diet to provide tdaessential amino acids cannot be synthesized . Digestion break the proteins down for use in the metabolism .