Transcription/translation Practice Questions

Question 1

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?

Accepted Answer

CUA

Answer

CCC

Answer

UAA

Answer

CCA

Answer

AUG

Question 2

An investigator is comparing DNA replication in prokaryotes and eukaryotes. He finds that the entire genome of E. coli (4 × 106 base pairs) is replicated in approximately 30 minutes. A mammalian genome (3 × 109 base pairs) is usually replicated within 3 hours. Which of the following characteristics of eukaryotic DNA replication is the most accurate explanation for this finding?

Accepted Answer

Simultaneous replication at multiple origins

Answer

Replication inhibition at checkpoint

Answer

Absence of telomerase enzyme activity

Answer

DNA compaction in chromatin

Answer

More efficient DNA polymerase activity

Question 3

An investigator studying protein synthesis in human stem cells isolates tRNA molecules bound to mRNA molecules. The isolated tRNA molecules have inosine in the 5' position of the anticodon; of these, some are bound to adenine, some to cytosine, and some to uracil at the 3' position of the mRNA codon. Which of the following properties of the genetic code is best illustrated by this finding?

Accepted Answer

Degeneracy

Answer

Unambiguity

Answer

Non-overlapping

Answer

Specificity of the start codon

Answer

Specificity of stop codons

Question 4

An 18-year-old African-American woman comes to the physician for the evaluation of worsening fatigue that started 1 year ago. Physical examination shows mild jaundice and splenomegaly. Laboratory studies show:
Hemoglobin 10.4 g/dL
Mean corpuscular hemoglobin concentration 43% Hb/cell
Platelet count 220,000/mm3
Reticulocyte count 7%
A peripheral blood smear shows target cells and erythrocytes with hemoglobin crystals. Which of the following is the most likely underlying cause of this patient's findings?

Accepted Answer

Replacement of glutamate by lysine in beta-globin chain

Answer

Acquired mutation of membrane-bound glycosylphosphatidylinositol anchor

Answer

Decreased conversion of oxidized glutathione into its reduced form

Answer

Replacement of glutamate by valine in beta-globin chain

Answer

Reduced production of beta-globin due to a mutation in the HbB gene

Question 5

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

Accepted Answer

A tRNA with the UUU anticodon can bind to either AAA or AAG codons

Answer

Charged tRNA contains energy needed for peptide bonds to form

Answer

The last nucleotide provides specificity for the given amino acid

Answer

There are more amino acids than possible codons

Answer

The genetic code is preserved without mutations

Question 6

An investigator is studying the genetic profile of an isolated pathogen that proliferates within macrophages. The pathogen contains sulfatide on the surface of its cell wall to prevent fusion of the phagosome and lysosome. She finds that some of the organisms under investigation have mutations in a gene that encodes the enzyme required for synthesis of RNA from a DNA template. The mutations are most likely to reduce the therapeutic effect of which of the following drugs?

Accepted Answer

Rifampin

Answer

Pyrazinamide

Answer

Ethambutol

Answer

Streptomycin

Answer

Levofloxacin

Question 7

A clinical trial is being run with patients that have a genetic condition characterized by abnormal hemoglobin that can undergo polymerization when exposed to hypoxia, acidosis, or dehydration. This process of polymerization is responsible for the distortion of the red blood cell (RBC) that acquires a crescent shape and the hemolysis of RBCs. Researchers are studying the mechanisms of the complications commonly observed in these patients such as stroke, aplastic crisis, and auto-splenectomy. What kind of mutation leads to the development of the disease?

Accepted Answer

Missense mutation

Answer

Silent mutation

Answer

Splice site

Answer

Nonsense mutation

Answer

Frameshift mutation

Question 8

A mutant stem cell was created by using an inducible RNAi system, such that when doxycycline is added, the siRNA targeting DNA helicase is expressed, effectively knocking down the gene for DNA helicase. Which of the following will occur during DNA replication?

Accepted Answer

DNA is not unwound

Answer

The RNA primer is not created

Answer

The two melted DNA strands reanneal

Answer

DNA supercoiling is not relieved

Answer

Newly synthesized DNA fragments are not ligated

Question 9

An investigator is studying the incidence of sickle cell trait in African American infants. To identify the trait, polymerase chain reaction testing is performed on venous blood samples obtained from the infants. Which of the following is required for this laboratory technique?

Accepted Answer

Primers complementary to target DNA sequences

Answer

Single-stranded binding proteins

Answer

Ligation of Okazaki fragments

Answer

Complete genome DNA sequence

Answer

RNA-dependent DNA polymerase

Question 10

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?

Accepted Answer

Podocyte foot process effacement

Answer

Normal podocyte foot process interdigitation

Answer

Mesangial cell proliferation

Answer

Endothelial cell fenestration

Answer

Glomerular basement membrane thickening

Transcription/translation

Study Resources

Lessons

Questions

Flashcards

Lessons

RNA polymerase structure and function

Promoters and transcription factors

Initiation of transcription

Elongation and termination of transcription

Post-transcriptional modifications

RNA splicing and alternative splicing

Translation initiation

Elongation and termination of translation

Post-translational modifications

Protein folding and chaperones

Regulation of gene expression

Epigenetic mechanisms

RNA interference and microRNAs

Practice Questions

Flashcards

About Transcription/translation for USMLE

Lessons in Transcription/translation

Master Transcription/translation