A nerve fibre cannot be stimulated during the absolute refractory period of a previous stimulus because

• Sodium permeability remains high  

• Sodium-potassium pump does not operate

• Voltage gated calcium channels remain closed

• Potassium conductance remains low

22.

ATP driven pumps hydrolyze ATP to ADP and phosphate and use the energy released to pump ions or solutes across a membrane. There are many classes of these pumps and representatives of each are found in all prokaryotic and eukaryotic cells. Which of the following statements about these pumps is NOT correct?

• P-type pumps ate multipass transmembrane proteins which phosphorylate themselves during pumping and involve in ion transport.

• F-type pumps normally use the H⁺ gradient across the membrane to drive the synthesis of ATP.

• V-type pumps normally use voltage gradient for transport of small molecules.   

• ABC tranpsorters primarily pump small molecules across cell membrane.

Mutants of lac Y (Y^-) gene of E. coli do not synthesize the lactose permease protein. The following statements refer to the behavior of lac Y^- mutants under different experimental conditions.

A. No synthesis of β- galactosidase when Y^- cells are induced with lactose.

B. Synthesis of β- galactosidase when cells are induced with lactose.

C. No synthesis of β- galactosidase when cells are induced with IPTG.

D. Synthesis of β- galactosidase when cells are induced with IPTG.

E. The cells induced with IPTG cannot grow in the presence of TONPG (TONPG is a compound, whose uptake is mediated by lactose permease and cleaved by β- galactosidase to release a toxic compound).

F. Cells induced with IPTG can grow in the presence of TONPG.

Which combination of the above statements is correct?

• A, D and F      

• B, C and E

• A, C and F

• A, C and E

The consequence of this recombination will be the formation of:

A. A dicentric and an accentric chromosome in meiosis I as the chiasmata gets terminated.

B. No dicentric or acentric chromosome but appearance of deletion and duplication in both the chromosomes.

C. All non-viable gamestes.

D. Non-viable gametes from crossover products.

Which of the above statements are correct?

• A and B

• A and C

• A and D  

• B and C

With reference to lac operon, what will be the phenotype of an E.coli strain having a genotype i^-o⁺y^-/F’i⁺o^cz^-y⁺?

• Constitutive for both β-galactosidase and lac permease.

• Inducible for both β-galactosidase and lac permease.

• Inducible for β-galactosidase and constitutive for lac permease.

• Constitutive for β-galactosidase and inducible for lac permease.

Which nitrogen of adenosine gets protonated if the pH of the nucleoside is lowered from 7 to 3?

• N1

• N3

• N7

• N9

Phosphatidylserine, an important component of biological membrane, is located in

• The outer leaflet but flipflops to the inner leaflet under specific conditions.

• Both the leaflets.

• The middle of the bilayer

• The inner leaflet but flipflops to outer leaflet under specific conditions.  

Major disadvantage of using liposome as a targeted drug delivery vehicle is that

• It gets internalized by phagocytosis inside lysosomes.    

• It is very unstable and has low shelf-life.

• It gets intercalated in cell membranes.

• Its drug entrapment efficiency is very low.

All cytosolic proteins have  nuclear export signals that allow them to be removed from the nucleus when it reassembles after

• Meiosis

• Mitosis

• Both mitosis and meiosis

• DNA replication

Spematogonial stem cell undergoes extensive metamorphosis to become a spermatozoan. Meiosis leads to the formation of spermatids containing 22 autosomes and one sex chromosome. A male mouse was found in a colony which always produces only female pups upon mating. Which one of the following is a possible reason?

• Spermiogenesis was defective.

• All spermatogonial stem cells contained only X and no Y chromosome.

• Activation of the Y chromosome-linked post-meiotic death-related gene may lead to such a situation.   

• Activation of the X chromosome-linked post-meiotic death-related gene may lead to such a situation.