ABSTRACT
Proteins are biological molecules that perform a wide array of tasks in cells. For example, antibodies are proteins that protect cells from foreign invaders. Transcription factors are proteins that turn genes on and off at the proper times. Enzymes are proteins that catalyze the thousands of chemical reactions that occur in cells. Recall from Chapters 22 to 25 that enzymes also are used as essential tools that allow biotechnologists to manipulate nucleic acids. Proteins are important in the research laboratory and in biotechnology companies where they are produced in large quantities for medical and industrial applications.
