Final answer:
A hydrophobic amino acid is insoluble in water and tends to avoid contact with it, grouping with other hydrophobic amino acids. They are important in protein structure and function, especially in creating the three-dimensional form and in proteins that span cell membranes.
Step-by-step explanation:
Understanding Hydrophobic Amino Acids
A hydrophobic amino acid is characterized by its tendency to be insoluble in water, often featuring aliphatic or aromatic side chains such as Ala, Val, Leu, Ile, Pro, Met, Phe, Trp. These amino acids exhibit hydrophobic interactions, where the 'R' groups (side chains) aggregate away from water, exhibiting repulsive forces towards water and attractive forces between each other. These hydrophobic amino acids are key contributors to protein structure, as they often orient themselves towards the interior of proteins, away from aqueous environments. This behavior is crucial for the formation of the protein’s three-dimensional structure, particularly in membrane-spanning proteins. Hydrophobic amino acids contrast with hydrophilic amino acids, which are soluble in water and include Gly, Ser, Thr, Cys, Tyr, Asp, Asn, Glu, Gln, Lys, Arg, His.
The hydrophobicity of these amino acids influences protein folding and function. For example, in proteins that cross cell membranes, hydrophobic amino acids tend to line up along the membrane-spanning regions, stabilizing the protein within the lipid bilayer. Furthermore, the aromatic amino acids—phenylalanine, tyrosine, and tryptophan—contribute to the property of proteins known as fluorescence, due to their ability to absorb and emit light.