Biomolecules Test - 89

Isoenzymes are an unique example in which the same reaction may be catalyzed by two or more different molecular forms of an enzyme. The multiple forms, called isozymes or isoenzymes, may occur in the same species, in the same tissue, or even in the same cell. The different forms of the enzyme generally differ in kinetic or regulatory properties, in the cofactor they use (NADH or NADPH for dehydrogenase isozymes, for example), or in their subcellular distribution (soluble or membrane-bound). Isozymes may have similar, but not identical, amino acid sequences, and in many cases they clearly share a common evolutionary origin. One of the first enzymes found to have isozymes was lactate dehydrogenase (LDH), which, in vertebrate tissues, exists as at least five different isozymes separable by electrophoresis. However, isoenzymes follow the same general mechanism of enzyme action, i.e., decreasing the activation energy of substrates for a reaction.

Enzymes are biological catalysts. The multitude of biochemical reactions that make cellular metabolism possible are due to enzymes. The isolation and crystallization of urease by James Sumner in 1926 provided a breakthrough in early enzyme studies. Sumner found that urease crystals consisted entirely of protein, and he postulated that all enzymes are proteins. In the absence of other examples, this idea remained controversial for some time. Only in the1930s, was Sumners conclusion widely accepted, after John Northrop and Moses Kunitz crystallized pepsin, trypsin, and other digestive enzymes and found them also to be proteins.

The curve shows the effect of substrate concentration on the rate of enzyme catalyzed reaction. It shows that increasing substrate concentration increases the rate of reaction until a point comes when all the active sites of enzyme molecules are saturated with substrates and increasing the substrate concentration has no effect on the rate of reaction. The presence of enzyme inhibitor would reduce the reaction rate. The formation of enzyme complex is shown in the graph of the free energy level of the reaction mixture to the progress of the reaction. The  graph is showing the relation between the rate of reaction and substrate concentration, not the pH of the reaction mixture. Thus, the correct answer is option A.

The building up and breaking down of protoplasm involves two main process anabolism and catabolism which together forms metabolism. Proteins are always present in living matter and therefore play an important role in the anabolic and catabolic activities of protoplasm.

According to Chargaff’s rule, in all cellular DNAs, regardless of the species, number of adenosine residues is equal to number of thymidine residues which means that A = T; and the number of guanosine residues is equal to the number of cytidine residues; G = C. Hence that the sum of the purine residues equals the sum of the pyrimidine residues; i.e., A + G = T + C. Here [G] = 32% therefore, % of [C] is also 32%. Thus, [A] + [T] = 100 - 64 = 36 %. [A] = 18% and [T] = 18%. 

According to the given graph, reaction start at the temperature 10 degree and the reaction rate is increased as the temperature is increased from 10 degree to 40 degree. It may be result of increased kinetic energy of the reactant molecules which in turn increase the collisions. The reaction rate is decreased as the temperature is increased above 40 degree and come to a halt at 70 degree. It may be due to altered enzymatic structure as higher temperatures.

Arginosuccinase (argininosuccinate lyase) catalyzes the formation of arginine and fumarate from argininosuccinate, the last step in the biosynthesis of arginine. 

Isolation of protoplasts is readily achieved by treating cells/tissues with a suitable mixture of cell wall degrading enzymes. Usually, a mixture of pectinase or macerozyme (0.1-1.9%) and cellulose (1-2%) is appropriate for most plant materials. Hemicellulase may be necessary for some tissues.