Giardia intestinalis can cause disease in several different mammalian species, including humans. Giardia organisms (G. intestinalis) that infect humans are similar morphologically to those that infect other mammals, thus they have been considered a single species. However, G. intestinalis has been divided into different subgroups based on their host and a few other characteristics. In 1999, a DNA sequence comparison study tested the hypothesis that these subgroups actually constitute different species. The following phylogenetic tree was constructed from the sequence comparison of rRNA from several subgroups of G. intestinalis and a few other morphologically distinct species of Giardia. The researchers concluded that the subgroups of Giardia are sufficiently different from one another genetically that they could be considered different species

By examining the phylogenetic tree diagrammed in the figure above, what conclusion can you draw about the species G. microti?

#Question id: 4264

#Unit 3. Fundamental Processes

A classic biochemical experiment nicely illustrated the point that the ribosome recognizes tRNA and not the amino acid that it is carrying. In that following observation were made. Which of them can be correct.

A. The cysteine attached to cysteine-tRNACys can be converted to an alanine by chemical reduction to give alanine-tRNACys.

B. Alanine-tRNACys introduces alanines at codons that specify insertion of cysteine.

C. Different mechanism is used to incorporate selenocyteine on tRNA as selenocysteine is incorporated into proteins by chemical modification after translation

D. Selenocysteine is generated enzymatically from serine carried on a special tRNA that is charged by serine-tRNA synthetase

E. Above examples can conclude that the translation machinery relies on the high fidelity of the aminoacyl-tRNA synthetases to ensure the accurate decoding of each mRNA

#Question id: 4265

#Unit 3. Fundamental Processes

48S pre initiation complex includes

#Question id: 4266

#Unit 3. Fundamental Processes

48S pre initiation complex is

#Question id: 4267

#Unit 3. Fundamental Processes

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: 4268

#Unit 3. Fundamental Processes

23S rRNA catalyze peptide-bond formation as

A. base pairing between the 23S rRNA and the CCA ends of the tRNAs

B. A- and P-sites positions the a-amino group of the aminoacyl-tRNA to attack the carbonyl group of the growing polypeptide attached to the peptidyl-tRNA

C. Entropic catalysis is involved

#Question id: 4269

#Unit 3. Fundamental Processes

The kinase P-TEFb

A. Is recruited to polymerase by transcriptional activators

B. Phosphorylates the serine 2&5 of the CTD repeats for elongation

C. Phosphorylates SPT5 and TAT-SF1