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1. Which of the following statements explains how N-formylmethionine (fMet) is incorporated only in response to the 5'-AUG initiation codon in E. coli, given that methionine has only one codon?
A. Methionine is only ever found as the first amino acid in a polypeptide
B. There is only one tRNA with the CAU anticodon.
C. Only Met-tRNAmCl can bind to a specific ribosomal entry site.
D. The N-formyl group on methionine prevents fMet from entering interior positions in a polypeptide.
E. fMet is always incorporated at interior AUG sites and then deformylated after translation.
2. Which of the following is not true of the second step of translational elongation in bacteria?
A. Puromycin inhibits translation by mimicking the 3' end of an aminoacyl-tRNA
B. The carboxyl group oxygen of the A-site amino acid is the nucleophile in peptide bond formation.
C. A peptide bond is formed between the two amino acids bound by the tRNAs in the A and P sites.
D. The growing polypeptide chain is transferred to the tRNA in the A site.
E. The a-amino group of the A-site amino acid attacks the carbonyl carbon of the P-site amino acid.
3. Which of the following is not a function of the release factors of bacterial translation termination'?
A. mediating the hydrolysis of the terminal peptidyl-tRNA bond
B. assisting in the initial folding of the nascent polypeptide chain
C. releasing the last uncharged tRNA from the P site
D. recognition of a stop codon
E. occupation of the ribosomal A site
4. Which of the following is NOT a possible outcome of the CRISPWCas9 system?
A. disruption of a gene
B. repair of a gene
C. deletion of a chromosome
D. blocking or enhancing gene expression
E. all of the above are possible
5. Which of the following is NOT true of the reaction catalyzed by RNA polymerases?
A. Template DNA is copied in the 3' to 5' direction.
B. The 3'-hydroxyl group of the growing RNA strand is the nucleophile.
C. The reaction is magnesium ion dependent.
D. U residues are incorporated into the RNA to pair with T residues of the template.
E. The RNA molecule is synthesized in the 5' to 3' direction.
6. The sequence of the messenger RNA molecule (primary transcript) synthesized from a DNA molecule with a template strand having the sequence 5'-ATGCTACCGTTA-3' is:
A. 5 '-UACGAUGGCAAU-3'
B. 5 '-UAACGGUAGCAU-3'
C. 5'-AUGCUACCGUUA-3'
D. 5'-AUUGCCAUCGUA-3'
E. None of these choices is correct

Respuesta :

Answer: D. The N-formyl group on methionine prevents fMet from entering interior positions in a polypeptide.

okpalawalter8

Answer:

  • 1) Option D (The N-formyl group on methionine prevents fMet from entering interior positions in a polypeptide)
  • 2) Option B (The carboxyl group oxygen of the A-site amino acid is the nucleophile in peptide bond formation)
  • 3) Option B (assisting in the initial folding of the nascent polypeptide chain)
  • 4) Option A (disruption of a gene)
  • 5) Option A (Template DNA is copied in the 3' to 5' direction)
  • 6) Option A (5 '-UACGAUGGCAAU-3')

Explanation:

1) Option D(The N-formyl group on methionine prevents fMet from entering interior positions in a polypeptide)

2) Option B (The carboxyl group oxygen of the A-site amino acid is the nucleophile in peptide bond formation)  is not responsible for the second part of the translation elongation in bacteria.

3) Option B (assisting in the initial folding of the nascent polypeptide chain) This is because the folding of the protein does not takes place in the ribosome. Afetr the binding of the release factor into the A site. the nascent peptide is released from the ribosomal complex. This nascent peptide is now present in the primary state and folding occur in secondary or tertiary state of the protein

4) Option A (disruption of a gene)

5) Option A (Template DNA is copied in the 3' to 5' direction) is wrong and not copied by the RNA polymerase. RNA polymerasze copy the Coding strands of the DNA in 3' to 5' direction

6) Option A (5 '-UACGAUGGCAAU-3') During transcrition of the RNA from the template DNA.is done by the enzyme RNA polymerase.

This RNA pol. copy the all the neucleotide from the coding strand of the DNA but replace Thymine by Uracil.

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