Biochemistry is defined as the chemistry of biology. The science of biochemistry has also been called physiological chemistry and biological chemistry. Biochemistry is concerned chiefly with the chemistry of biological processes; it attempts to utilize the tools and concepts of chemistry particularly organic and physical chemistry, for elucidation of the living system. This chapter covers the review of structure, composition and functions of cell, prokaryote and eukaryote cell organization, and microscope. Biochemistry is used to learn about the biological processes which take place in cells and organisms. Applications of the basic principles of biochemistry are essential to the nursing profession. The correct diagnosis, nursing care plans, treatment, prevention and control of infectious diseases depend on a sound knowledge of medical biochemistry.