Translation initiation — MCQs

A codon is an mRNA sequence consisting of 3 nucleotides that codes for an amino acid. Each position can be made up of any 4 nucleotides (A, U, G, C); therefore, there are a total of 64 (4 x 4 x 4) different codons that can be created but they only code for 20 amino acids. This is explained by the wobble phenomenon. One codon for leucine is CUU, which of the following can be another codon coding for leucine?

An 8-year-old girl is brought to the emergency room for a 6-hour history of fever, sore throat, and difficulty swallowing. Physical examination shows pooling of oral secretions and inspiratory stridor. Lateral x-ray of the neck shows thickening of the epiglottis and aryepiglottic folds. Throat culture with chocolate agar shows small, gram-negative coccobacilli. The patient's brother is started on the recommended antibiotic for chemoprophylaxis. Which of the following is the primary mechanism of action of this drug?

In translation, the wobble phenomenon is best illustrated by the fact that:

An investigator is studying the modification of newly formed polypeptides in cultured eukaryotic cells. After the polypeptides are released from the ribosome, a chemically-tagged protein attaches covalently to lysine residues on the polypeptide chain, forming a modified polypeptide. When a barrel-shaped complex is added to the cytoplasm, the modified polypeptide lyses, resulting in individual amino acids and the chemically-tagged proteins. Which of the following post-translational modifications has most likely occurred?

A 12-year-old male presents to the emergency department following several days of facial edema. A urinalysis confirms proteinuria and hematuria. Once admitted, a kidney biopsy is viewed under an electron microscope to confirm the diagnosis of minimal change disease. In the following electron micrograph, what process occurs in the structure marked with an arrow?

An investigator is studying the genotypes of wingless fruit flies using full exome sequencing. Compared to wild-type winged fruit flies, the wingless fruit flies are found to have a point mutation in the gene encoding wing bud formation during embryogenesis. The point mutation in the gene causes the mRNA transcript to have a 'UUG' segment instead of an 'AUG' segment. Which of the following processes is most likely affected by this mutation?

Given the mRNA sequence shown below, if translation were to start at the first base, what would the tRNA anticodon be for the last amino acid translated in the chain? 5'----GCACCGGCCUGACUAUAA---3'

Expression of an mRNA encoding for a soluble form of the Fas protein prevents a cell from undergoing programmed cell death. However, after inclusion of a certain exon, this same Fas pre-mRNA eventually leads to the translation of a protein that is membrane bound, subsequently promoting the cell to undergo apoptosis. Which of the following best explains this finding?

A 3-year-old boy is brought to the physician because of arm pain following a fall that took place 5 hours ago. According to his mother, the boy was running in the yard when he fell and injured his right arm. The boy is crying and clutching his arm. During the past year, he has been brought in 4 other times for extremity pain following falls, all of which have been diagnosed as long bone fractures. He is at the 10th percentile for height and 25th percentile for weight. His temperature is 37.3°C (99.1°F), pulse is 95/min, respirations are 21/min, and blood pressure is 97/68 mm Hg. His right forearm is diffusely erythematous. The patient withdraws and yells when his forearm is touched. His left arm has two small ecchymotic regions overlying the elbow and wrist. A photograph of his face is shown. An x-ray of the right forearm shows a transverse mid-ulnar fracture with diffusely decreased bone density. Which of the following is the most likely cause of this patient's symptoms?

An investigator is studying the rate of wound healing by secondary intention. He performs a biopsy of a surgically debrided wound 1 day and 5 days after the initial surgical procedure. The second biopsy shows wound contraction, endothelial cell proliferation, and accumulation of macrophages. The cells responsible for wound contraction also secrete a protein that assembles in supercoiled triple helices. In which of the following structures does this protein type play an important structural role?