Large molecule formed by amino acids that directs chemical reactions in the body.
The four functions of proteins:
Structural support - often when attached to parts of the cell's scaffolding or cytoskeleton
Recognition - binding sites on some proteins can serve to identify the cell to other cells, such as those of the immune system
Communication - receptor proteins, protruding out from the plasma membrane, can be the point of contact for signals sent to the cell via traveling molecules, such as hormones
Transport - Proteins can serve as channels through which materials can pass in and out of the cell