1. Syllabus to be covered till 31 st November Naindeep Kaur Resource person Biotech(E)- first year

2. Enzymes Enzymes are biological molecules that catalyze(i.e., increase the rates of) chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates sufficient for life. Enzyme activity can be affected by other molecules. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, pressure, chemical environment (e.g., pH), and the concentration of substrate.

3. The catalytic activity of many enzymes depends on the presence of small molecules termed cofactors. an enzyme without its cofactor is referred to as an apoenzyme; the complete, catalytically active enzyme is called a holoenzyme. Cofactors can be subdivided into two groups: metals and small organic molecules. The enzyme carbonicanhydrase, for example, requires Zn2+ for its activity Glycogen phosphorylase, which mobilizes glycogen for energy, requires the small organic molecule pyridoxal phosphate (PLP). Cofactors that are small organic molecules are called coenzymes. Often derived from vitamins, coenzymes can be either tightly or loosely bound to the enzyme. If tightly bound, they are called prosthetic groups.

4. Loosely associated coenzymes are more like cosubstrates because they bind to and are released from the enzyme just as substrates andproducts are. The use of the same coenzyme by a variety of enzymes and their source in vitamins sets coenzymes apart from normal substrates, however.

6. The Active Sites of Enzymes Have Some Common Features 1. The active site is a three-dimensional cleft formed by groups that come from different parts of the amino acid sequence. 2. The active site takes up a relatively small part of the total volume of an enzyme. 3. Active sites are clefts or crevices. 4. Substrates are bound to enzymes by multiple weak attractions. 5. The specificity of binding depends on the precisely defined arrangement of atoms in an active site.

7. Enzymes Decrease the Activation Energy.

8. The Michaelis-Menten Model Consider an enzyme that catalyzes the S to P by the following pathway: Our starting point is that the catalytic rate is equal to the product of the concentration of the ES complexand k 2. The rates of formation and breakdown of ES are given by: To simplify matters, we will work under the steady-state assumption. In a steady state, the concentrations of intermediates, in this case [ES], stay the same even if the concentrations of starting materials and products are changing. This occurs when the rates of formation and breakdown of the ES complex are equal. Setting the right-hand sides of equations 11 and 12 equal gives

9. By rearranging equation 13, we obtain Equation 14 can be simplified by defining a new constant, K M, called the Michaelis constant: Note that K M has the units of concentration. K M is an important characteristic of enzyme-substrate interactions and is independent of enzyme and substrate concentrations. Inserting equation 15 into equation 14 and solving for [ES] yields Now let us examine the numerator of equation 16. The concentration of uncombined substrate [S] is very nearly equal to the total substrate concentration, provided that the concentration of enzyme is much lower than that of substrate. The concentration of uncombined enzyme [E] is equal to the total enzyme concentration [E]T minus the concentration of the ES complex.

10. Substituting this expression for [E] in equation 16 gives By substituting this expression for [ES] into equation 10, we obtain The maximal rate, V max, is attained when the catalytic sites on the enzyme are saturated with substrate that is, when [ES] = [E]T. Thus, Substituting equation 22 into equation 21 yields the Michaelis-Menten equation:

13. Competitive inhibitionIn In competitive inhibition, the inhibitor and substrate compete for the enzyme (i.e., they can not bind at the same time).Often competitive inhibitors strongly resemble the real substrate of the enzyme For example, methotrexate is a competitive inhibitor of the enzyme dihydrofolate reductase, which catalyzes the reduction of dihydrofolate to tetrahyd rofolate.

14. Uncompetitive inhibition In uncompetitive inhibition, the inhibitor cannot bind to the free enzyme, only to the ES-complex. The EIS-complex thus formed is enzymatically inactive. This type of inhibition is rare, but may occur in multimeric enzymes.

15. Non-competitive inhibition Non-competitive inhibitors can bind to the enzyme at the binding site at the same time as the substrate,but not to the active site. Both the EI and EIS complexes are enzymatically inactive. Because the inhibitor can not be driven from the enzyme by higher substrate concentration (in contrast to competitive inhibition), the apparent V max changes. But because the substrate can still bind to the enzyme, the K m stays the same.

16. Biological function Enzymes serve a wide variety of functions inside living organisms. They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases. They also generate movement, with myosin hydrolyzing ATP to generate muscle contraction and also moving cargo around the cell as part of the cytoskeleton. Other ATPases in the cell membrane are ion pumps involved inactive transport. Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies. Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase.

17. An important function of enzymes is in the digestive systems of animals. Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines Different enzymes digest different food substances. In ruminants, which have herbivoros diets, microorganisms in the gut produce another enzyme, cellulase, to break down the cellulose cell walls of plant fiber. Amylases from fungi and plants:Production of sugars from starch, such as in making high-fructose corn syrup.In baking, catalyze breakdown of starch in the flour to sugar. Yeast fermentation of sugar produces the carbon dioxide that raises the dough.

18. Rennin, derived from the stomachs of young ruminant animals (like calves and lambs):Manufacture of cheese, used to hydrolyze protein Glucose isomerase: Converts glucose into fructose in production of high-fructose syrups from starchy materials. These syrups have enhanced sweetening properties and lower calorific values than sucrose for the same level of sweetness. Restriction enzymes, DNA ligase andpolymerases:Used to manipulate DNA in genetic engineering, important in pharmacology,agriculture and medicine. Essential forrestriction digestion and the polymerase chain reaction. Molecular biology is also important in forensic science.