MCQs

The Shine-Dalgarno sequence base-pairs with the 16S rRNA of the 30S subunit, aligning the bacterial ribosome with the start codon to initiate translation.

Because the glycosidic bonds project unevenly, the backbones wind asymmetrically around the axis, creating alternating major and minor grooves.

NMD is a surveillance mechanism that detects premature stop codons on transcripts and degrades them, preventing the accumulation of toxic, truncated proteins.

Polymerization relies on the cleavage of pyrophosphate (PPi​→2Pi​) to provide the forward driving force; blocking this halts the reaction.

Mutilating a splice site prevents the spliceosome from recognizing the intron-exon boundary, leading to intron retention or exon skipping during splicing.

G-C pairs are bound by three hydrogen bonds, meaning G-C rich fragments require higher temperatures to denature than A-T rich sequences of the same length.

XP is caused by defects in the NER pathway, which is responsible for cutting out UV-induced pyrimidine dimers and bulky DNA distortions.

Inhibiting HDAC keeps histones acetylated, neutralizing their positive charges and keeping chromatin open (euchromatin) to boost transcription.

Without a functional termination response, the polymerase runs past the end of the gene, creating a long, un-terminated read-through transcript.

Intercalating agents distort the helix by stretching the backbone, which tricks DNA polymerase into inserting or omitting bases, causing frameshift mutations.

Huntington's disease is a classic trinucleotide repeat disorder where a CAG expansion in the HTT gene produces a toxic, polyglutamine-expanded huntingtin protein.

Z-DNA is a left-handed helical variant with a zigzag sugar-phosphate backbone, favored by repeating purine-pyrimidine steps, high salt, or methylation.

Unwinding the helix creates torsional strain and positive supercoils ahead of the moving polymerase; without topoisomerase to relieve this stress, transcription stalls.

The linear sequence of nucleotide codons inside exons determines the exact order of amino acids added during protein translation.

Each phosphate group in the phosphodiester backbone loses a hydrogen atom at cellular pH, giving the exterior of the DNA a negative charge.

Thymine is a pyrimidine base specific to DNA, whereas RNA uses uracil as the complementary partner for adenine.

The mass of a gene depends on its length; longer nucleotide sequences contain more base pairs, increasing the total molecular weight.

Enhancers are regulatory DNA sequences that bind activator proteins, interacting with the promoter to boost transcription.

The Watson-Crick model shows DNA as a right-handed double helix, where two complementary strands twist around a central longitudinal axis.