MCQs

Converting a CAA codon (coding for glutamine) into a UAA codon introduces a premature stop signal, producing a shorter, tissue-specific protein.

Promoter hypermethylation creates a structural barrier that blocks the binding of transcription factors and RNA polymerase, shutting down transcription.

The creation of a cryptic splice site inside an intron leads the spliceosome to misidentify the intron boundaries, incorporating junk sequence into the mature mRNA.

Telomerase is a reverse transcriptase that carries its own internal RNA molecule to serve as a structural template for lengthening chromosome ends.

The branch-point sequence contains an adenine residue whose 2'-OH attacks the 5' splice site, a critical step for lariat formation during splicing.

Puromycin structurally mimics an aminoacyl-tRNA, entering the A site and forming a premature peptide link that causes the peptide chain to detach.

The 2'-OH group on the ribose ring structurally prevents the RNA-DNA hybrid from matching the B-form geometry, forcing it into an A-form configuration.

Without a protective 3' poly-A tail, newly exported cytoplasmic mRNA molecules are quickly targeted and broken down by cellular exonucleases.

Alternative splicing allows exons to be skipped or combined in different ways, creating diverse protein products from one primary transcript.

The ribosome checks only the codon-anticodon match. The 3'-UUG-5' anticodon will pair with a 5'-AAC-3' codon, incorrectly introducing methionine.

In basic solutions, the 2'-OH group of ribose is deprotonated, launching a nucleophilic attack on the adjacent phosphorus atom that breaks the RNA backbone.

The sigma subunit is a transient initiation factor that grants the core prokaryotic RNA polymerase structural specificity to bind promoters.

In historical genetic code experiments, UUU was discovered to be the specific codon that codes for the amino acid phenylalanine.

Small nucleolar RNAs (snoRNAs) reside within the nucleolus and act as guide RNAs that direct the biochemical modification and splicing of pre-rRNA.

The structural domains of rRNA inside the A and P binding sites form precise non-covalent contacts to align the tRNA for peptide synthesis.

Double-stranded RNA is a hallmark of viral replication; eukaryotic cells use the Dicer and RISC pathways to recognize and destroy it.

The D-loop gets its name from containing dihydrouracil and plays a key structural role in recognition by aminoacyl-tRNA synthetase.

The size and weight of an mRNA molecule depend entirely on the length of the specific polypeptide chain it is meant to code for.

Short-lived mRNA allows bacteria to quickly shut down old metabolic pathways and transcribe new genes when conditions change.