121.

E. coli is being grown in a medium containing both glucose and lactose. On depletion of glucose, expression of β-galactosidase will

• remain unchanged

• increase

• decrease

• initially decrease and then increase

Histone deacetylase (HDAC) catalyses the removal of acetyl group from N-terminal of histones. Which amino acid of histone is involved in this process?

• Lysine

• Arginine

• Asparagine

• Histidine

Lateral diffusion of proteins in the membrane can be followed and the diffusion rate calculated by

• Atomic force microscopy

• Scanning electron microscopy

• Transmission electron microscopy

• FRAP

Which of the following is NOT an example of transmembrane transport between different subcellular compartments?

• Transport from the cytoplasm into the lumen of the endoplasmic reticulum.

• Transport from the endoplasmic reticulum to the Golgi complex.

• Transport from stroma into thylakoid space.

• Transport from mitochondrial intermembrane space into the mitochondrial matrix.

Which one of the following best describes the symplast pathway of water flow from the epidermis to endodermis in a plant root?

• Water moves through cell walls and extracellular spaces without crossing any membrane.

• Water travels across the root cortex via the plasmodesmata.

• Water crosses the plasma membrane of each cell in its path twice, one on entering and once on exit.

• Transport across the tonoplast.

If nondisjunction occurs in meiosis I, which of the following scenario is most likely to occur?

• Two gametes will be n + 1 and two will be n - 1.

• One gamete will be n + 1, two will be 'n' and one will be n - 1.

• Two gametes will be normal and two will be n - 1.

• Two gametes will be normal and two will be n + 1.

During cell cycle progression from G₁ to S, cyclin D-CDK4 phosphorylates Rb and reduces its affinity for E2F. E2F dissociates from Rb and activates S-phase gene expression. Over-expression of protein 'A' arrests G₁ phase progression.

Which of the following statements is TRUE?

• 'A' inhibits Rb-E2F interaction.

• 'A' inhibits CDK4 activity.

• 'A' phosphorylates E2F

• 'A' degrades Rb.

Cells in S-phase of the cell cycle were fused to cells in the following stages of cell cycle: (a) G₁ phase, (b) G₂ phase; (c) M phase. These cells were then grown in medium containing tritiated thymidine. Maximal amount of freshly labelled DNA is likely to be obtained in S-phase cells fused with

• G₁ phase cells

• G₂ phase cells

• M phase cells

• Both G₁ and G₂ phase cells

Addition of the antibiotic cephalexin to growing E. coli cells leads to filamentation of the cells, followed by lysis. Cephalexin is an inhibitor of

• protein synthesis

• DNA synthesis

• peptidoglycan synthesis

• RNA polymerase

Inversions are considered as cross-over suppressors because

• Homozygous inversions are lethal and thus they do not appear in next generation.

• Inversion heterozygotes, i.e. one copy having normal chromosome and its homologue having inversion, does not allow crossing over to occur as they cannot pair at all.

• Due to inversion present, four chromosomes take part in the pairing and crossing over events and make the structure difficult for separation and gamete formation.

• The pairing and crossing overs do occur in inversion heterozygotes but the gametes having cross over products are lethal.