enzyme in biology for engineers subject.pptx

Enzyme ppt

1. Enzyme

2. Mechanism of enzyme action The enzymes act on a substrate by combining with the substrate molecules to form an enzyme-substrate complex. Enzymes (E) have specific active sites for the attachments of substrate (S) molecule where an enzyme can form intimate relationship with the substrate. It is presumed that the enzyme-substrate combination (ES) brings about a deformation in some of the bonds in substrate molecule which favours the reaction to produce a product.

3. Leonor Michaelis  and  Maud Menten  gave an equation in 1913 to explain the mechanism of enzyme action. It depends upon the lowering of  activation energy . 

4. According to Michaelis Menten’s equation, the enzyme-substrate complex can reversibly dissociate into (enzyme plus substrate) and further proceed to give (enzyme plus product ). In a catalyzed reaction or an enzyme’s presence, the substrate rapidly reaches the transition state due to decreased activation energy. The enzyme reduces the energy required (activation energy) for the substrate to form products.

5. For enzymes that exhibit Michaelis–Menten kinetics, plots of velocity-versus-substrate concentration are hyperbolic.

6. Enzyme velocity The rate of an enzyme-catalyzed reaction is often called its velocity. Enzyme velocities are normally reported as values at time zero (initial velocity, symbol V o ; μmol min -1 ). This is because the rate is fastest at the point where no product is yet present as the substrate concentration is greatest before any substrate has been transformed to product. A typical plot of product formed against time for an enzyme-catalyzed reaction shows an initial period of rapid product formation which gives the linear portion of the plot. This is followed by a slowing down of the enzyme rate as substrate is used up and/or as the enzyme loses activity. V  is obtained by drawing a straight line through the linear part of the curve, starting at the zero time-point. The slope of this straight line is equal to V .

7. The Michaelis–Menten equation : where,  K m  = (k2 + k3)/k1 and V max  is the maximum velocity. The Michaelis constant, Km, is equal to the sum of the rates of breakdown of the enzyme–substrate complex over its rate of formation, and is a measure of the affinity of an enzyme for its substrate. The rate of formation of products (the velocity of the reaction) is related to the concentration of the enzyme–substrate complex: v = k 3 [ES] V max  is reached when the entire enzyme is in the enzyme–substrate complex. K m  is the substrate concentration at which v = 1/2 V max . When [S] = K m , substitution of K m  for [S] in the Michaelis–Menten equation yields v = 1/2 Vmax .