The 3D structure of the complete Escherichia coli ribosome with bound mRNA and tRNAs revealed that the very amino terminus of one protein (L27) does reach into the active site. This finding suggested a role for this protein in catalysis. To test this possibility, the nine amino acids at the L27 amino terminus that were in close proximity to the active site were eliminated by mutation. The following possible outcomes were found to be correct as

A. The resulting cells produced ribosomes with reduced but detectable peptidyl transferase activity

B. Region of the L27 protein contributes to peptidyl transferase activity

C. The mutant ribosomes, didn’t synthesised wildtype levels of cells

D. Vast majority of this increase in peptide bond formation is retained, even without the presence of L27 in the active site

E. The most likely role for L27 is to correctly position one or more of the RNA components of the active site

#Question id: 867

#Unit 1. Molecules and their Interaction Relevant to Biology

Match the correct diseases with their precursors

#Question id: 868

#Unit 1. Molecules and their Interaction Relevant to Biology

Which statements is incorrect about ‘The chaperonin-assisted catalysis of protein folding’

A. The non-cooperative nature of ATP binding establishes GroEL as an allosteric enzyme.

B. In GroEL with a total of 14 subunits in two heptameric rings are observed.

C. In vivo GroES is composed of seven identical subunits whilst GroEL is composed of 14 larger subunits.

D. Gro-EL being called chaperonin60 (cpn60) and Gro-ES chaperonin10 (cpn10).

#Question id: 869

#Unit 1. Molecules and their Interaction Relevant to Biology

Which statements are correct regarding protein folding

A. Many molecular chaperones were first described as heat shock proteins (Hsp) because Their rate of synthesis is increased at elevated temperatures

B. The renaturation of a denatured protein in vitro may not entirely mimic the folding of a protein in vivo.

C. Molecular chaperones are essential proteins that bind to only partially folded polypeptide chains.

D. Molecular chaperones function to lift folding polypeptides out of the false minima in their folding funnel.

#Question id: 870

#Unit 1. Molecules and their Interaction Relevant to Biology

Choose correct statements about ‘Protein Disulfide Isomerase’ in protein folding

A. Oxidized PDI catalyzes the rearrangement of a polypeptide’s non-native disulfide bonds via disulfide interchange reactions to yield native disulfide bonds.

B. Reduced PDI catalyzes the initial formation of a polypeptide’s disulfide bonds through the formation of a mixed disulfide.

C. Protein disulfide isomerase contains the conserved active site motif of Cys-Xaa-Xaa-Cys found in thioredoxin and shares a similar role to the Dsb family of proteins found in E. coli.

D. Under more reducing conditions with thiols in the active site the enzyme reshuffles disulfides (isomerase) in target proteins.

#Question id: 871

#Unit 1. Molecules and their Interaction Relevant to Biology

According to ‘Energy–entropy phenomenon’ for protein folding correct combinations of possible conformations

#Question id: 872

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following statements is not true about HSP 70 family.

A. They have a molecular weight near 70,000 and are abundant in cells stressed by elevated temperature.

B. Bind to regions of unfolded polypeptides that are rich in hydrophilic residues

C. Hsp70 proteins not  block the folding of certain proteins that must remain unfolded untill they have been translocated across a membrane.

D.) It releases polypeptides in a cycle that uses energy from ATP hydrolysis.