Final answer:
Proteins perform specific functions due to their unique amino acid sequences, which determine their three-dimensional structures, allowing them to bind tightly and specifically to other molecules.
Step-by-step explanation:
The characteristic of a protein molecule that allows it to perform a specific function is its ability to bind specifically and tightly with other molecules. This specificity is due to the unique sequence of amino acids in each protein, which determines its three-dimensional structure and consequently its function. For example, enzymes are proteins that act as biological catalysts to speed up chemical reactions, with each enzyme being highly specific for its substrates. Similarly, antibodies bind to specific foreign particles, marking them for destruction by the immune system. Transport proteins, like hemoglobin, bind and carry molecules such as oxygen throughout the body. The unique folding and shape of each protein allow it to interact with specific molecules, which is essential for carrying out its role in the cell.