#Question id: 10348
#Unit 6. System Physiology – Plant
During ammonium assimilation, requires two enzymes converting ammonium to amino acids. Each of which is Glutamine synthetase (GS), given below some statements about GS ;
a) GS transfers the amide group of glutamine to 2-oxoglutarate, yielding two molecules of glutamate
b) it requires a divalent cation such as Mg2+, Mn2+, or Co2+ as a cofactor
c) Plants contain two classes of GS, one in the cytosol and the other in root plastids or shoot chloroplasts
d) The cytosolic forms are expressed in germinating seeds or in the vascular bundles of roots and shoots and produce glutamate for intercellular nitrogen transport
e) The GS in root plastids generates amide nitrogen for local consumption; the GS in shoot chloroplasts reassimilates photorespiratory NH4+
f) Light and carbohydrate levels alter the expression of the cytosolic forms of the enzyme, but they have little effect on the plastid forms.
Which of the following statements is correct?
#Question id: 10347
#Unit 6. System Physiology – Plant
NH4+ is toxic to plants, inhibit dinitrogenase and also interfere energy metabolism by dissociating ATP formation from ETC in both mitochondria and chloroplasts. What will plant cells do to avoid this problem?
a) Plant cells avoid ammonium toxicity by rapidly converting the ammonium generated from nitrate assimilation or photorespiration into nitrate
b) Plant cells avoid ammonium toxicity by rapidly converting the ammonium generated from nitrate assimilation or photorespiration into amino acids
c) The pathway for this conversion involves the sequential actions of glutamine synthetase (GS) and glutamate synthase (GOGAT)
d) The pathway for this conversion involves the sequential actions of Aspartate aminotransferase (Asp-AT) and Asparagine synthetase (AS)
Which of the above statements is incorrect?
#Question id: 10346
#Unit 6. System Physiology – Plant
Nitrite reductase will convert nitrite to ammonium. There are two types of nitrite reductase characteristics given below;
a) Both nitrite reductase consist of a single 63kD polypeptide
b) In leaf chloroplasts and root plastids contain different forms of the nitrite reductase enzyme
c) In shoot nitrite reductase directly dependent on the light reaction by the ferredoxin, it activates nitrite reductase in choloroplast
d) NADPH in the roots is provided by pentose phosphate pathway, it also activate nitrite reductase in the plastids
Which of the correct statement about nitrite reductase characteristics?
#Question id: 10345
#Unit 6. System Physiology – Plant
In Leaf Chloroplasts and root plastids contain different forms of the enzyme, nitrite reductase such as
a) Roots contain fd-dependent nitrite reductase
b) Shoots contain NADPH dependent nitrite reductase
c) Shoots contain fd-dependent nitrite reductase
d) Roots contain NADPH dependent nitrite reductase
Which one of the following is correct combination?
#Question id: 10344
#Unit 6. System Physiology – Plant
Some of the following caracteristics of Nitrite reductase, which one of the is incorrect?
#Question id: 10342
#Unit 6. System Physiology – Plant
Nitrate reductase is an important enzyme for nitrate assimilation. Given below some regulation of nitrate reductase activity through phosphorylation and dephosphorylation.
a) Light, and other environmental factors stimulate a protein phosphatase that dephosphorylates a key serine residue in the hinge 1 region of nitrate reductase and thereby activates the enzyme
b) In Dark, and Mg2+ stimulate a protein kinase that phosphorylates the same serine residues, which then interact with a 14-3-3 inhibitor protein, and thereby inactivate nitrate reductase
c) In Light, and Mg2+ stimulate a protein kinase that phosphorylates the serine residues, and thereby activate nitrate reductase
d) In Dark, and other environmental factors stimulate a protein phosphatase that dephosphorylates a key serine residue in the hinge 1 region of nitrate reductase and thereby inactivates the enzyme
Which of the following statements about regulation of nitrate reductase is correct?