Enzyme
There are approximately 40,000 enzymes living in one human cell, each responsible for a chemical reaction. Enzymes are complex 3D protein molecules created by amino acids, forming a unique sequence that produces hydrogen bonds, eventually formulating an enzyme within plants and animals (Boyle & Senior, 2002). Working alongside other molecules, they uphold a stable reaction system. The function of an enzyme is to aid and increase chemical reactions and organise metabolism, while maintaining homeostasis (Geddes & Grosset, 2000). Within living cells hundreds of reactions are occurring, each requiring a particular enzyme. Enzymes act as natural catalysts within the body, by increasing the rate of chemical reactions but not altering its own structure (Boyle & Senior, 2002). There are two models to help describe how an enzyme works: the lock and key hypothesis (appendix A) or an induce fit (appendix B) (Tortora & Grabowski, 2003). Enzymes are very particular, having their own shape with a precise surface construction known as the active site, allowing it to recognise and secure the correct substrate, bolting together like a key fitting a lock, hence the lock and key hypothesis (Tortora & Grabowski, 2003). At any given time within a catalysed enzyme reaction, the number of substrate molecules is greater than the number of enzyme molecules therefore allowing more reactions to take place (Tortora & Grabowski, 2003). The substrate corresponds with the size and shape of the active site so they compatibly fit, this works optimally at correct temperatures and pH levels (Wright, 2000). The reaction will only succeed with the correct substrate molecule attaching to the correct enzyme, creating an enzyme-substrate complex (Geddes & Grosset, 2000). Once the reaction has occurred, the process can repeat itself, leaving the active site free to be used over and over. If the shape of an enzyme is altered by certain malfunctions, pH or temperature for example, then the active site