A 24-year-old woman comes to the office due to a persistent facial rash. The patient easily develops "sunburns" after sun exposure and her fingers "turn blue" in cold weather. She has also felt more fatigued than usual. Physical examination shows a facial rash in a butterfly distribution that spares the nasolabial folds. Laboratory studies reveal several types of autoantibodies directed against components of the cell nucleus. One specific antibody targets proteins complexed with small nuclear ribonucleic acid. These protein-ribonucleic acid complexes are most likely involved in which of the following cellular functions?

Question

A 24-year-old woman comes to the office due to a persistent facial rash.  The patient easily develops "sunburns" after sun exposure and her fingers "turn blue" in cold weather.  She has also felt more fatigued than usual.  Physical examination shows a facial rash in a butterfly distribution that spares the nasolabial folds.  Laboratory studies reveal several types of autoantibodies directed against components of the cell nucleus.  One specific antibody targets proteins complexed with small nuclear ribonucleic acid.  These protein-ribonucleic acid complexes are most likely involved in which of the following cellular functions?

Quizplus · Accepted Answer

11ec160b_36fa_3009_9249_713315c50d41_MD0001_00 This patient's constellation of symptoms (eg, malar rash, photosensitivity, Raynaud phenomenon ["blue fingers"], fatigue) is consistent with systemic lupus erythematosus, an autoimmune disease associated with anti-Smith antibodies (highly specific). Smith protein normally complexes with small nuclear RNA (snRNA) in the cytoplasm, forming small nuclear ribonucleoproteins (snRNPs). Transcription occurs in the nucleus and is catalyzed by 3 types of RNA polymerases, leading to the formation of messenger RNA (mRNA), ribosomal RNA (rRNA), transport RNA (tRNA), and snRNA. RNA polymerase II synthesizes both mRNA and snRNA, the latter of which combines with specific proteins to form snRNPs. mRNA synthesis occurs in 2 stages. During the first, the DNA template is transcribed into a complementary strand of pre-mRNA. In the second, pre-mRNA is processed into mature mRNA through the following steps: Mature mRNA then transfers the genetic code to the cytoplasm and serves as a template for protein synthesis (translation). (Choices A and D) Polyadenylation of RNA transcripts is performed by the enzyme polyadenylate polymerase. This process stabilizes mRNA, helping it exit the nucleus. (Choices B and F) During eukaryotic DNA replication, DNA polymerase δ elongates Okazaki fragments of the lagging strand. These Okazaki fragments are later joined by the enzyme DNA ligase. (Choice C) During translation, aminoacyl-tRNA synthetases catalyze the linkage of tRNAs to their corresponding amino acids. Each enzyme recognizes a specific amino acid and all of the tRNAs that match that amino acid. Educational objective: Small nuclear RNA (snRNA) is synthesized by RNA polymerase II in the nucleus and complexes with specific proteins to form small nuclear ribonucleoproteins (snRNPs). snRNPs are an essential component of spliceosomes, which remove introns from pre-mRNA to form mature mRNA. Patients with systemic lupus erythematosus can have autoantibodies directed against snRNPs (eg, anti-Smith antibody). __________ References: Spliceosome structure and function. (http://www.ncbi.nlm.nih.gov/pubmed/21441581) Anti-Sm and anti-RNP antibodies. (http://www.ncbi.nlm.nih.gov/pubmed/15804705)

A 24-Year-Old Woman Comes to the Office Due to a Persistent