According to Cooper (1988) '... a literature review uses as its database reports of primary or original scholarship, and does not report new primary scholarship itself. The primary reports used in the literature may be verbal, but in the vast majority of cases reports are written documents.
Reactive oxygen species. Reactive oxygen species (ROS) are chemically reactive chemical species containing oxygen. Examples include peroxides, superoxide, hydroxyl radical, and singlet oxygen. In a biological context, ROS are formed as a natural byproduct of the normal metabolism of oxygen and have important roles in cell signaling and homeostasis.
1. Enzymes catalyse only those reactions that happen naturally. 2. Enzymes are specific: each enzyme is responsible for only 1 kind of reaction, because they are shaped to work with only a certain substrate that matches enzyme's active site. 3. Enzyme changes its conformation when substrate bonds to its active site. This creates stress on the substrate's bond making them easier to break (induced fit model) 4. Enzymes are not changed by the reaction. They are needed in small quantities, because they are reused.