In isoelectric focusing experiments, proteins are separated on the basis of their

• relative content of only positively charged residues.

• relative content of only charged residues.

• relative content of positively and negatively charged residues.

• mass to charge ratios

Which one of the following is unfavourable for protein folding?

• Hydrophobic interaction

• van der Waals interaction

• Conformational entropy

• Hydrogen bonding

The maximum number of hydrogen bonds that can form between H₂N-NH₂ (hydrazine) and water is

• 2

• 1

• 3

• 4

The peptide unit (C^α - C'O - NH - C^α) is planar due to

• restriction around C^α - C' bond

• restriction around C' - N bond

• restriction around N - C^α bond

• hydrogen bonding between the carbonyl oxygen and imino hydrogen of the peptide backbone.

Which one of the following is the most appropriate statement regarding folded proteins?

• Charged amino acid side chains are always buried.

• Charged amino acid side chains are seldom buried.

• Non-polar amino acid side chains are seldom buried.

• Tyrosine residues are always buried.

Molecules primarily responsible for the formation of lipid raft are

• phosphatidylserine and phosphatidyl choline

• phosphatidyl inositol and cholesterol

• glycosylphosphatidylinositol and cholesterol

• sphingolipids and cholesterol

You are studying a protein that inserts itself into a model membrane (liposomes) during a reconstitution process. The protein has an N-terminal, 18-amino acid hydrophilic segment that is located on the outside of the membrane, a 19-amino acid hydrophobic transmembrane segment flanked by negatively and positively charged amino acids, and a C-terminal domain that resides inside the lumen (as depicted below in the form of a cartoon).

For proper reconstitution of the protein, which of the following strategies will be appropriate?

• Increase the number of negatively charged amino acids in the N-terminal.

• Increase the number of positively charged amino acids in the C-terminal.

• Removal of positively charged amino acids from the C-terminal.

• Increase the length of the hydrophobic segment.

Aquaporins are a class of proteins that are relatively abundant in plant membranes. Following are certain statements regarding the properties of aquaporins:

A. Aquaporins form water channels in membrane.

B. Some aquaporins also transport uncharged molecules such as NH₃.

C. The activity of aquaporins is not regulated by phosphorylation.

D. The activity of aquaporin is regulated by calcium concentration and reactive oxygen species.

Which one of the following combinations of above statements is correct?

• A, B, and D

• B, C, and D

• A, C, and D

• A, B, and C

In terpene biosynthesis pathways, three acetyl-CoA are joined together stepwise to form mvalonic acid. Which one of the following three steps is required by mevalonic acid to form ispentenyl diphosphate or isopentenyl pyrophosphate (IPP)?

• Pyrophosphorylation, decarboxylation and dehydration

• Alkylation, pyrophosphorylation and decarboxylation

• Methylation, dehydration and alkylation

• Phosphorylation, carboxylation and methylation

Patients suffering from familial hypercholesterolemia (FH) are mostly homozygous for the defective gene and have profoundly elevated levels of serum cholesterol. The reason may be that the gene for highly specific receptor for LDL is either defective or missing in these patients. In an experiment, cells were taken from both normal individual and homozygotes (FH) subjects, incubated in buffer with ¹²⁵I-labeled LDL in presence or absence of access unlabeled LDL for various time periods and them ¹²⁵I-labeled LDL bound to cells was measured. Which of the following is the bestfit graph for the above experiment?