The lambda repressor binds as a dimer to critical sites on the bacteriophage lambda genome to keep the lytic genes turned off, which allows the bacteriophage lambda genome to be maintained as a silent resident in the bacterial genome. Each molecule of the repressor consists of an N-terminal DNA-binding domain and a C-terminal dimerization domain. Upon induction (for example, by irradiation with ultraviolet light), the genes for lytic growth are expressed, bacteriophage lambda progeny are produced, and the bacterial cell lyses to release the viral progeny. Induction is initiated by cleavage of the lambda repressor at a site between the DNA-binding domain and the dimerization domain. In the absence of bound repressor, RNA polymerase initiates transcription of the lytic genes, triggering lytic growth.

A. Binding as monomers will be sufficiently weak that they do not compete with the binding of RNA polymerase. As a result, the genes for lytic growth will be turned on.

B. Binding as monomers will be sufficiently strong that they will compete with the binding of RNA polymerase. As a result, the genes for lysogenic growth will be turned on

C. The affinity of the dimeric lambda repressor for its binding site is the sum of all the interactions made by each DNA-binding domain. An individual DNA-binding domain will make just half the contacts and provide just half the binding energy as the dimer.

D. The affinity of the dimeric lambda repressor for its binding site is the sum of all the interactions made by each DNA-binding domain. An individual DNA-binding domain will make just double the contacts and provide just double the binding energy as the dimer.

Given that the number (concentration) of DNA-binding domains is unchanged by cleavage of the repressor, which of above outcomes will be possible?

#Question id: 10341

#Unit 6. System Physiology – Plant

The accumulation of nitrate that results from diminished nitrate reductase activity, this symptoms is caused by

#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?

#Question id: 10343

#Unit 6. System Physiology – Plant

In many plants, nitrate is assimilated in the root as well as in the shoot according to their native place. Some of the given statements about nitrate assimilation;

a) If plants native to temperate region assimilate NO3^- at root

b) If plants native to temperate region assimilate NO3^- at shoot

c) Plants native to tropical or subtropical region assimilate NO3^- at root

d) Plants native to tropical or subtropical region assimilate NO3^- at shoot

Which of the following combination from above statements is correct?

#Question id: 10344

#Unit 6. System Physiology – Plant

Some of the following caracteristics of Nitrite reductase, which one of the is incorrect?

#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?