Protein
Proteins have a variety of shapes and functions.
Fibrous, hydrophobic proteins like keratin and collagen have hydrophobic amino acids on their surface and are not soluble in water.
Proteins associated with the cell membrane have a layer of hydrophobic amino acids
sandwiched between layers of hydrophilic amino acids.
Protein function as carrier molecules like hemoglobin, as antibodies, and as enzymes.
Proteins are also
embedded in membranes where they function in transport or signal transfer.
Enzymes
Enzymes are an important class of proteins that catalyze biochemical reactions without being consumed in the reaction. Enzymes speed up reactions by lowering the energy required by the system to initiate the reaction. Reactions can be exergonic (release energy) or endergonic (require energy).