MCQs

A polysome (or polyribosome) consists of a single mRNA strand being translated simultaneously by several moving ribosomes to amplify protein yield.

snRNAs combine with specific proteins to form snRNPs ("snurps"), which build the spliceosome machinery responsible for removing introns.

A triplet code consisting of three consecutive nucleotides provides the minimum variations (43=64) needed to code for 20 amino acids.

Polycistronic mRNA is characteristic of prokaryotes, where a single promoter controls an operon containing multiple related open reading frames.

Ribonucleases (RNases) degrade mRNA molecules once their translational utility is exhausted, preventing overproduction of proteins.

Unlike other rRNAs transcribed by RNA Polymerase I in the nucleolus, 5S rRNA is transcribed by RNA Polymerase III in the nucleoplasm.

While the 2D layout is a cloverleaf, the functional 3D conformation is an L-shape stabilized by complex non-Watson-Crick hydrogen bonding.

Post-transcriptional enzymatic modifications generate unique bases in tRNA to stabilize its complex three-dimensional tertiary structure.

The carboxyl group of the amino acid forms a high-energy ester linkage with the 3'-OH group of the terminal adenosine on the tRNA.

Introns are intervening sequences that do not code for proteins and are spliced out before the mRNA leaves the nucleus.

RNA Polymerase II is exclusively responsible for the transcription of all protein-coding structural genes into mRNA in eukaryotes.

Heterogeneous nuclear RNA (or pre-mRNA) represents the raw, unprocessed transcript containing both exons and introns.

The peptidyl transferase center is entirely composed of conserved domains of the large subunit's ribosomal RNA (ribozyme activity).

The eukaryotic 80S ribosome dissociates into a 60S large subunit and a 40S small subunit; the 40S subunit contains the 18S rRNA.

Transfer RNA bridges the gap by binding to a specific mRNA codon on one end while carrying the corresponding amino acid on the other.

The Shine-Dalgarno sequence is a purine-rich region upstream of the start codon that pairs with the 16S rRNA of the prokaryotic ribosome.

The 2' -OH group acts as a nucleophile that can attack the adjacent phosphodiester backbone, making RNA chemically less stable than DNA.

Eukaryotic RNA Polymerase III handles the transcription of smaller, structural non-coding RNAs including tRNA and 5S rRNA.

Alternative splicing allows different combinations of exons to be joined, producing multiple distinct protein isoforms from a single gene.