Enzyme Chain to Chain Association. Series of Enzymes In certain cases enzymes act in a series of chemical reactions in a particular order to complete a metabolic pathway such as respiration or photosynthesis. Arrangement The successive enzymes containing these reactions are normally present together in a precise order of reaction such that substrate molecules can be literally handed on‟ from one enzyme to another forming an enzyme to enzyme chain. In this way the products from one step in pathway are transferred to the enzyme catalyzing the next step. Feed Back Inhibition. Feedback inhibition, is inhibition of the activity of an enzyme, by end product of metabolic pathway when it exceeds the limits. Point To be Memorize. Most enzymes do not float about in a kind of cytoplasmic „soup‟ but are attached to membranes systems inside the cell in specific and orderly arrangements. Mitochondria and chloroplasts are good examples of this. Models of Enzymes.

Lock and key Model Induce Fit Model Proposed by Emil Fischer (1890) proposed a lock and Key model to visualize substrate and enzyme interaction. On the basis of new evidences Koshland (1959) proposed its modified form. This is known as induce fit Model. Statement According to this model, As one specific key can open only a specific lock, in the same manner a specific enzyme can transform only one substrate into products(s). According to this model when a substrate combines with an enzyme, it induces changes in the enzyme structure. The change in structure enables the enzyme to perform its catalytic activity more effectively. Flexibility Active site is rigid structure. There is no modification or flexibility in the active site before, during or after the enzyme action and it is used only as a template. Active site is flexible and may be modified during enzymatic actions. Acceptance. Later studies did not support this model in all reactions. This is most accepted model.