The hydrolysis of lactose is catalysed by b-galactosidase as given below

Which of the following could be correct mechanism for this hydrolysis reaction?

A. Nucleophilic attack by the carboxylate group of Glu/Asp on the C-1 carbon atom of the galactose moiety within glucose, releasing glucose and forming an intermediate with the galactose linked to the enzyme through an ester linkage. Water then attacks this carbon atom, displacing the glutamate carboxylate and releasing galactose.

B. Electrophilic attack by the carboxylate group of Glu/Asp on the C-1 carbon atom of the galactose moiety within glucose, releasing glucose and forming an intermediate with the galactose linked to the enzyme through an ester linkage. Water then attacks this carbon atom, displacing the glutamate carboxylate and releasing galactose.

C. Nucleophilic attack by the carboxylate group of Lys/Arg/His or bivalent cation on the C-1 carbon atom of the galactose moiety within glucose, releasing glucose and forming an intermediate with the galactose linked to the enzyme through an ester linkage. Water then attacks this carbon atom, displacing the glutamate carboxylate and releasing galactose.

#Question id: 11827

#Unit 6. System Physiology – Plant

Which of the following enzyme is involved in the rate-limiting step in ethylene biosynthesis?

#Question id: 11828

#Unit 6. System Physiology – Plant

Given some enzymes of ethylene biosynthetic pathway and its character;

A) ACC synthase                                                               i) It is an unstable, cytosolic enzyme. Its level is regulated by environmental and internal factors, such as wounding, drought stress, flooding, and auxin

B) ACC oxidase                                                                  ii) It catalyzes the last step in ethylene biosynthesis, the conversion of ACC to ethylene

                                                                                                iii) Its activity can be the rate-limiting step in ethylene biosynthesis

                                                                                                iv) That is encoded by a multigene family that is differentially regulated

                                                                                                v) It is present in such low amounts in plant tissues and is very unstable and also difficult to purify the enzyme  for biochemical analysis

                                                                                                vi) These enzymes belong to the Fe2+/ascorbate oxidase superfamily

Find out the correct combination from the given enzymes and its character?

#Question id: 11829

#Unit 6. System Physiology – Plant

The certain cyclic olefin compounds, have been shown to block ethylene breakdown without inhibiting ethylene action?

#Question id: 11830

#Unit 6. System Physiology – Plant

Not all the ACC found in the tissue is converted to ethylene, ACC can also be converted to a conjugated form, which does not appear to break down and accumulates in the tissue?

#Question id: 11831

#Unit 6. System Physiology – Plant

A volatile compound is a strong competitive inhibitor of ethylene binding______

#Question id: 11832

#Unit 6. System Physiology – Plant

Ethylene production and action can be inhibited by various types of inhibitors, some statements about  the inhibitor is given below, which one of the following is incorrect?