Question

7. In bacteria the elongation stage of protein synthesis does not involve: A) aminoacyl-tRNAS B) EF-Tu C) GTP D) IF-2 E) peptidyl transferase Which of the following best describes the cholesterol molecule? A) Amphipathic B) Nonpolar, charged C) Nonpolar, uncharged D) Polar, charged E) Polar, uncharged The enzyme that attaches an amino acid to a tRNA (aminoacyl-tRNA synthetase): A) always recognizes only one specific tRNA. B) attaches a specific amino acid to any available tRNA species. C) attaches the amino acid at the 5' end of the tRNA. D) catalyzes formation of an ester bond. E) splits ATP to ADP +P 10. It is possible to convert the Cys that is a part of Cys-tRNAY to Ala by a catalytic reduction. If the resulting Ala-tRNA were added to a mixture of (1) ribosomes, (2) all the other tRNAs and amino acids, (3) all of the cofactors and enzymes needed to make protein in vitro, and (4) mRNA for hemoglobin, where in the newly synthesized hemoglobin would the Ala from Ala-tRNACY" be incorporated? A) Nowhere; this is the equivalent of a nonsense mutation. B) Wherever Ala normally occurs c) Wherever Cys normally occurs D) Wherever either Ala or Cys normally occurs E) Wherever the dipeptide Ala-Cys normally occurs 11. Which one of the following statements about the transcription attenuation mechanism is true? A) In some operons (e.g., the his operon), attenuation may be the only regulatory mechanism. B) Sequences of the trp operon leader RNA resemble an operator. C) The leader peptide acts by a mechanism that is similar to that of a repressor protein. D) The leader peptide gene of the trp operon includes no Tip codons. E) The leader peptide is an enzyme that catalyzes transcription attenuation. 12. Direct electron transfer from a singlet reduced species to a triplet oxidizing species is: A) quantum-mechanically forbidden B) common C) promoted by reactive nitrogen D) A and C E) None of the above 13. The biological role of restriction enzymes is to: A) aid recombinant DNA research. B) degrade foreign DNA that enters a bacterium. C) make bacteria resistant to antibiotics. D) restrict the damage to DNA by ultraviolet light E) restrict the size of DNA in certain bacteria.

Answer 1

7. D. IF-2

IF-2 involves is initiation process and all other involves in elongation process

8. A. Amphipathic, An amphipathic molecule is a molecule that has both polar and non-polar parts.

Cholesterol is an amphipathic molecule (like phospholipids), meaning it has both hydrophilic and hydrophobic regions

• Cholesterol’s hydroxyl (-OH) group is hydrophilic and aligns towards the phosphate heads of phospholipids
• The remainder of the molecule (steroid ring and hydrocarbon tail) is hydrophobic and associates with the
• phospholipid tails

9. A. Always recognises only one specific t-RNA

Because there is specific tRNA synthetase for a particular amino acid.

Each aminoacyl-tRNA synthetase has a binding site that recognizes a specific amino acid, and other binding areas that recognize a particular tRNA through unique identity sites at the acceptor stem and/or anticodon loop of the tRNA.

10. C Wherever Cys normally occurs

There is a specific aminoacyl tRNA synthetase for each of the 20 amino acids.

Once an amino acid is attached to a tRNA, the specificity for protein synthesis resides solely with the tRNA portion of the aminoacylated tRNA molecule.

The anticodon of the tRNA base pairs with the codon of the mRNA.

Here, cysteine can be put on tRNACys (Cys-tRNACys), chemically modified to the amino acid alanine (Ala-tRNACys), and then used in a biochemical system for protein synthesis. The resulting polypeptides now made in the biochemical reaction have alanine at positions normally occupied by cysteine.