Which one of the following combinations is the correct pairing of ligands with their receptors?

(i)FGF	a. Patched
(ii) Hedgehog	b. Frizzled
(iii) Wnt	c. Receptor tyrosine kinase

• i - c; ii - a; iii - b

• i - a; ii - c; iii - b

• i - b; ii - c; iii - a

• i -c; ii - b; iii - a

A virus infects a particular cell type, integrates its genome into a site that contains a proto-oncogene, transforms the cell and increases the level of a protein 'X', which increases cellular proliferation. A compound 'P' is known to increase the level of tumor suppressor proteins in that cell type whereas a compound 'Q' helps in stimulating a protein 'Z' that can bind to 'X' rendering it inactive. Which one of the following graphs correctly represents the mode of action of 'P' and 'Q'?

Cadherins mediate Ca²⁺-dependent cell-cell adhesion and play an important role in embryonic development by changing the adhesive properties of cell. Aggregation of nerve cells to form an epithelium is correlated with the appearance of N-cadherins on cell surface and vice versa. N-CAM (neural cell adhesion molecules) belongs to Ig-SF (immunoglobulin super family) and involved in fine tuning of adhesive interactions. In order to see the effect of mutations of N-cadherin and N-CAM, two sets of mice were generated. Ser A-mice with mutation in N-cadherin and set B-mice with mutation in N-CAM. Which of the following results is most likely to occur?

• Mice of both set A and set B will die in early development.

• Mice of set A will die in early development but mice of set  B will develop normally and show mild abnormalities in the development of the nervous system.

• Mice of Set A will show mild abnormalities in the development of the nervous system whereas mice of set B will die early in development.

• Mice of both set A and set B develop normally as other cell adhesion molecules will compensate for the mutations.

In an experiment peritoneal macrophages were isolated from strain A of guinea pig. These cells were then incubated with an antigen. After the antigen pulsed macrophages processed the antigen and presented it on their surface, these were mixed with T cells from (i) strain A or (ii) strain B (a different strain of guinea pig) or (iii) F1 progeny of strain A × B. T cell proliferation was measured in response to antigen pulsed macrophages T cells of which strain of guinea pig will be activated?

• Strain A only

• Strain B only

• Strain A and F1 progeny

• Strain B and F1 progeny

Immunoglobulins have therapeutic applications in cancer treatment, infection clearance and targeted drug delivery. For this reason, immunoglobulins are briefly cleaved by the enzyme pepsin. Following are some of the statements regarding the brief digestion of immunoglobulin by pepsin.

(i) F(ab)₂ fragment is generated which retains the antigen binding activity.

(ii) F(ab) fragment having antigen binding activity and the crystallisable F_c fragment are generated.

(iii) The fragment generated on incubation with a proper antigen forms a visible precipitate.

(iv) The fragment generated is incapable of forming a visible precipitate on incubation with a proper antigen.

Which of the above statements are correct?

• (i) and (ii)

• (i) and (iii)

• (i) and (iv)

• (ii) and (iii)

As topoisomerases play an important role during replication, a large number of anticancer drugs have been developed that inhibit the activity of these enzymes. Which of the following statements is NOT true about topoisomerase as a potential anticancer drug target?

• As cancer cells are rapidly growing cells, they usually contain a higher level of topoisomerases.

• The transient DNA breaks created by topoisomerases are usually converted to permanent breaks in the genome in the presence of topoisomerase targeted drugs.

• As cancer cells often have impaired DNA repair pathways, they are more susceptible towards topoisomerase targeted drugs.

• The drugs which specifically target topoisomerases, usually do not affect normal fast-growing cells.

Glycophorin of red blood cell (RBC) membrane spans the membrane only once and the N-terminal is projected intracellularly and the C-terminal is exposed to the cytosolic side. With the help of antibodies (labelled with fluorophores against N-terminal and C-terminal peptides, orientation of glycophorin across membrane can be verified. Which one of the following statements is correct?

• Intact RBC can be labelled with C-terminal antibody.

• Permeabilized RBC can be labelled with C-terminal antibodies as well as N-terminal antibodies.

• Intact RBC cannot be labelled with N-terminal antibodies.

• Inside out ghost of RBC can be labelled with N-terminal antibodies.

The di- and tripeptides are transported in the enterocytes by peptide transporter 1 that requires:

• Na⁺

• Ca⁺⁺

• H⁺

• Cl^-

Which one of the following best defines an oncogene?

• An oncogene never codes for a cell cycle protein, which promotes cell proliferation.

• Oncogenes are always involved in inherited forms of cancer.

• An oncogene codes for a protein that prevents a cell from undergoing apoptosis.

• An oncogene is a dominantly expressed mutated gene that renders a cell advantageous towards survival.

Following are some of the characteristics of MHC class I and class II molecules except one which is applicable only for MHC class I. Identify the appropriate statement.

• They are expressed constitutively on all nucleated cells.

• They are glycosylated polypeptides with domain structure.

• They are involved in the presentation of antigen fragments to cells.

• They are expressed on the surface membrane of B cells.