141.

In a confirmatory test for HIV, one or more viral antigens are detected in the blood of patients. Following are the steps to be performed for the experiment:

A. Transfer of viral antigens to nitrocellulose paper.

B. Incubation with the buffer containing antibodies specific for viral antigens.

C. Separation of viral antigens by SDS-PAGE.

D. Detection of bands by enzyme-linked secondary antibody.

Identify the correct sequence steps be performed for the experiment.

• A-B-C-D

• B-C-D-A

• C-A-B-D

• C-B-A-D

The mean and standard deviation of serum cholesterol in a population of senior citizens are assumed to be 200 and 24 mg/dl, respectively. In a random sample of 36 senior citizens, what values of cholesterol (to the nearest whole number) should lead to rejection of the null hypothesis at 95% confidence level?

• above 224

• above 248

• below 176 and above 224

• below 192 and above 208

The most important property of any microscope is its resolution (D) and can be calculated from the formula

D = 

where D is minimum distance between two distinguishable objects, λ is the wave length of incident light, α is the angular aperture and N is the refractive index of the medium. Given below are several suggestions to improve the resolution of a microscope:

A. decrease the wave length of incident light.

B. increase the wavelength of incident light.

C. use oil which has a higher refractive index.

D. use oil because of its lower refractive index.

Which one is the correct suggestion?

• A and C

• Only B

• Only D

• B and D

In response to a drug, changes in protein levels were examined in a cell line. A pulse chase experiment was performed using ³⁵S labeled methionine. In comparison to untreated samples, the following observations were made : few minutes after stimulation, protein X accumulates and this was followed by reduction in protein Y and Z. The correct interpretation of these observations would be:

• Protein X is a protease that degrades Y and Z.

• Protein X is a transcriptional repressor that controls expression of Y and Z.

• Expression of protein X and loss of Y and Z are unrelated.

• Information is not sufficient to distinguish between the three possibilities stated above.

A protein undergoes post-translational modification. In an experiment to identify the nature of modification, following experimental results were obtained.

A. Protein moved more slowly in an SDS-PAGE.

B. Isoelectric focusing (IEF) showed that there was no change in the pI.

C. Mass spectrometric analysis showed that the modification was on serine.

The modification that the protein undergoes is likely to be

• phosphorylation

• glycosylation

• ubiquitination

• ADP-ribosylation