Prognosis: β-Thalassemia trait does not cause mortality or significant morbidity. Patients should be informed of the genetic nature of their autosomal-recessive condition for family planning considerations because homozygous β-thalassemia (Cooley anemia) is a serious disorder.
Case-Related Questions: Choose the ONE best answer.
Q1. Mutations to the gene for β globin that result in decreased production of the protein are the cause of β-thalassemia. The mutations primarily affect gene transcription or posttranscriptional processing of the messenger RNA (mRNA) product. Which of the following statements concerning mRNA is correct?
A. Eukaryotic mRNA is polycistronic.
B. mRNA synthesis involves trans-acting factors binding to cis-acting elements.
C. mRNA synthesis is terminated at the DNA base sequence thymine adenine guanine (TAG).
D. Polyadenylation of the 5′-end of eukaryotic mRNA requires a methyl donor.
E. Splicing of eukaryotic mRNA involves removal of exons and joining of introns by the proteasome. Q2. HbA, a tetramer of 2 α and 2 β globin chains, delivers O2 from the lungs to the tissues and protons and CO2 from the tissues to the lungs. Increased concentration of which of the following will result in decreased O2 delivery by HbA? A. 2,3-Bisphosphoglycerate
B. Carbon dioxide
C. Carbon monoxide
D. Protons Q3. What is the basis for the increase in HbA2 and HbF (fetal Hb) in the βthalassemias?
Q4. Why is the allele-specific oligonucleotide (ASO) hybridization technique useful in the diagnosis of all cases of sickle cell anemia but not all cases of β-thalassemia?
Case 2: Skin Rash
Patient Presentation: KL is a 34-year-old woman who presents with a red, nonitchy rash on her left thigh and flu-like symptoms.
Focused History: KL reports that the rash first appeared a little over 2 weeks ago. It started out small but has gotten larger. She also thinks she is getting the flu because her muscles and joints ache (myalgia and arthralgia, respectively), and she has had a headache for the last few days. Upon questioning, KL reports that she and her husband took a camping trip through New England last month.
Pertinent Findings: The physical examination is remarkable for the presence of a red, circular, flat lesion ~11 cm in size that resembles a bullseye (erythema migrans) (see image at right). KL also has a low-grade fever.
Diagnosis: KL has Lyme disease caused by the bacterium Borrelia burgdorferi, which is transmitted by the bite of a tick in the genus Ixodes. Infected ticks are endemic in the Northeast region of the United States.
Treatment: KL is prescribed doxycycline, an antibiotic in the tetracycline family. Monitoring of KL will continue until all symptoms have completely resolved. Blood is drawn for clinical laboratory tests.
Prognosis: Patients treated with the appropriate antibiotic in the early stages of Lyme disease typically recover quickly and completely.
Case-Related Questions: Choose the ONE best answer.
Q1. Antibiotics in the tetracycline class inhibit protein synthesis (translation) at the initiation step. Which of the following statements about translation is correct?
A. In eukaryotic translation, the initiating amino acid is formylated methionine.
B. Only the charged initiating transfer RNA goes directly to the ribosomal A site.
C. Peptidyltransferase is a ribozyme that forms the peptide bond between two amino acids.
D. Prokaryotic translation can be inhibited by the phosphorylation of initiation factor 2.