The yeast Gal4 transcription activator comprises two domains: a DNA binding domain and an activation domain. The DNA-binding domain allows Gal4 to bind to appropriate DNA sequences located near genes that are required for metabolism of the sugar galactose. The activation domain binds to components of the transcriptional machinery (including RNA polymerase), attracting them to the promoter, so the regulated genes can be turned on. In the absence of Gal4, the galactose genes cannot be turned on. When Gal4 is expressed normally, the genes can be maximally activated. When Gal4 is massively overexpressed, however, the galactose genes are turned off. Choose correct explanation for this regulation?

A. In order for Gal4 to work properly, the DNA-bound Gal4 recruits many proteins, including RNA polymerase, to the promoter.

B. When there is too much Gal4 in the cell, the free and DNA-bound Gal4 will compete for the limited quantities of these other components.

C. In the presence of excess Gal4, those components are tied up in unproductive complexes with free Gal4, thereby preventing their recruitment to the promoter.

D. cells that massively overexpress Gal4 grow poorly because of the reduced availability of critical components of the transcription machinery.

E. Over concentration of Gal4 prevent suppressors to bind with DNA

#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: 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: 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: 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: 10349

#Unit 6. System Physiology – Plant

Elevated plastid levels of glutamine stimulate the activity of glutamate synthase (also known as glutamine:2- oxoglutarate aminotransferase, or GOGAT). Given below some of the statements about GOGAT, which one of the following is incorrect?

#Question id: 10350

#Unit 6. System Physiology – Plant

Ammonium can be assimilated via an alternative pathway rather than primary pathway which involves the sequential actions of glutamine synthetase(GS) and glutamate synthase(GOGAT), these alternative pathway catalyzes by enzyme known as,