In an experiment, cultured fibroblasts are mechanically lysed, and the membrane lipids and cellular proteins are chemically removed to isolate nucleic acids. The cellular extract containing the purified nucleic acids is incubated along with short sequences of repeated deoxythymidine residues fixed to latex beads. The solution is washed several times to remove unbound molecules. Which of the following types of nucleic acid is most likely to bind the strongest to the latex beads in this experiment?

Question

In an experiment, cultured fibroblasts are mechanically lysed, and the membrane lipids and cellular proteins are chemically removed to isolate nucleic acids.  The cellular extract containing the purified nucleic acids is incubated along with short sequences of repeated deoxythymidine residues fixed to latex beads.  The solution is washed several times to remove unbound molecules.  Which of the following types of nucleic acid is most likely to bind the strongest to the latex beads in this experiment?

Quizplus · Accepted Answer

11ec160b_3771_a9d8_9249_619be97b561c_MD0001_00 In the experiment described above, the poly-A tail on mature mRNA is most likely to bind the latex beads because the adenine residues in this tail would form complementary base pairs with the repeated deoxythymine residues fixed to the beads. Mature mRNA refers to mRNA that has been processed and is ready for nuclear export and translation into protein. mRNA processing (post-transcriptional modification) involves the following steps: 5' capping: A 7-methyl-guanosine cap is added to the 5' end of the mRNA. Polyadenylation: A poly-A tail (chain of adenine residues) is added to most eukaryotic mRNA molecules by poly-A polymerase. Poly-A tails are not transcribed from the DNA template. Instead, a consensus sequence (AAUAAA) located near the 3' end of the RNA molecule directs the addition of the poly-A tail. This tail protects the mRNA from degradation within the cytoplasm after it exits the nucleus. Splicing: The initial mRNA transcript (pre-mRNA) contains sequences from coding and noncoding regions of DNA, known as exons and introns, respectively. Spliceosomes (complexes of small nuclear ribonucleoproteins [snRNPs] and other proteins) remove introns containing GU at the 5' splice site and AG at the 3' splice site (Choice E). (Choice A) Aminoacyl-tRNA is tRNA charged with its amino acid. The cloverleaf structure of tRNA consists of a 3' CCA tail (amino acid binding site); a T loop abundant in ribothymidine, pseudouridine, and cytidine residues; a D loop rich in dihydrouridine residues; and an anticodon loop. (Choice C) DNA promoter regions help initiate transcription by binding transcription factors and RNA polymerase II. Promoter regions contain consensus sequences that are typically AT-rich (eg, TATA and CAAT boxes) or GC-rich (eg, GC box). (Choice D) Ribosomal RNA (rRNA) is a component of the ribosome that catalyzes peptide bond formation during translation. (Choice F) Telomeres are located at the ends of chromosomes and contain TTAGGG repeats, which are added by the enzyme telomerase (RNA-dependent DNA polymerase). Critical shortening in telomere length is thought to signal programmed cell death. Educational objective: The poly-A tail is not transcribed from DNA; instead, it is added as a post-transcriptional modification downstream of the consensus sequence (AAUAAA) located near the 3' end of the mRNA molecule. This tail protects mRNA from degradation within the cytoplasm after it exits the nucleus. __________ References: Ending the message: poly(A) signals then and now. (http://www.ncbi.nlm.nih.gov/pubmed/21896654)

In an Experiment, Cultured Fibroblasts Are Mechanically Lysed, and the Membrane