Structure of DNA

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.

Hypoxanthine pairs with cytosine, meaning the original template A-T pair becomes a G-C pair after a few rounds of replication, causing a transition mutation.

Triple-stranded H-DNA forms when a third single strand winds into the major groove of a duplex, binding via alternative Hoogsteen hydrogen bonds.

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

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

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

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

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

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.

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

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

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

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

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

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

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

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

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

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