111.

Which of the following statements is NOT true during the infection of plant cells with Agrobacterium?

• The protein products of virulence genes vir A and vir G perceive acetosyringone.

• The virB protein forms a connection between Agrobacterium and the plant cell and facilitates T-DNA transfer into the plant.

• The T-DNA is excised and bound to VirD2 protein.

• The T-DNA, after becoming coated with VirF binds to phosphorylated V1P1, which allows the complex to enter the plant’s nucleus.

Among existing technologies, which of the following vector systems would you prefer to use for generating a library for 140 kb eukaryotic genomic DNA fragments, while giving due consideration to size as well as stability of the insert?

• Phage

• Cosmid

• Bacterial artificial chromosome (BAC)    

• Yeast artificial chromosome (YAC)

If r denotes the correlation coefficient and m denotes the slope of the regression line, inter-changing X and Y axes would

• Change m but not r  

• Change r but not m

• Change both r and m

• Not change r or m

The use of biotinylated secondary antibody in ELISA

• Increases the sensitivity of the assay but compromises the specificity.

• Increases the sensitivity of the assay without compromising the specificity.  

• Does not alter either sensitivity or specificity.

• Decreases both sensitivity and specificity.

Which is the best method for checking mycoplasma contamination in a mammalian cell line?

• Southern hybridization

• ELISA

• PCRs

• Western hybridization

Differential scanning calorimetric study of calf thymus DNA was carried out to measure midpoint of thermal denaturation T_m, delta H_m (enthalpy change at T_m) and delta C_p (constant – pressure heat capacity change). It has been observed that delta C_p = 0, T_m = 75.5°C and delta H_m – 50.4 kcal/ mole. The Gibbs free energy change at 37°C is

• 25.5 kcal/ mole

• 2.6 kcal/ mole

• 0.6 kcal/ mole

• 5.6 kcal/ mole   

Hoechst 33342 is a membrane-permanent dye that fluoresces when it binds to DNA through an intercalating process. If a population of cells is incubated briefly with Hoechst dye and sorted in a flow cytometer, the cells display various of fluorescence if different phases of cell cycles as shown in the figure below (marked as X, Y, and Z)

Which of the following is correct?

• X is G₁, Y is G₂ + M and Z is S

• X is G₁, Y is S and Z is G₂ + M   

• X is G₁, Y is S and Z is G₂ + M   

• X is S, Y is G₁ and Z is G₂ + M

The scatter plot of growth rate and growth yield for 100 random environmental isolates of bacteria is shown below:

Which of the following can be inferred from the data?

• The two parameters are not related.

• Growth rate is inversely proportional to growth yield.

• Growth yield is negatively correlated with growth rate.

• High growth rate cannot be accompanied by high growth yield.  

Double-stranded DNA replicates in a semi-conservative manner. In an in vitro DNA synthesis reaction, dideoxy CTP and dideoxy CMP were individually added in excess (in separate reaction tubes) in addition to dNTPs and other necessary reagents. Rat of DNA synthesis was measure by incorporation of ³H-thymidine. The four graphs drawn below represent the rate of DNA synthesis in two separate reaction tubes.

Which of the following graphs represents the expected data?

A reporter cell line with stably integrated retroviral promoter-luciferase construct was transfected with an expression vector for a cellular protein. The protein seems to regulate the activation of the retroviral promoter as analyzed by luciferase activity assay. Which one of the following techniques will you use to show “in vivo” recruitment of the cellular protein on the integrated retroviral promoter?

• Electrophoretic mobility shift assay

• RNAse protection assay.

• DNAse hypersensitivity assay.

• Chromatin immunoprecipitation assay