MCQs

The structural framework of the DNA strand is formed by a repeating chain of deoxyribose sugars linked by neutral phosphodiester groups.

Silent mutations take advantage of the redundancy of the genetic code, where multiple codons translate into the same amino acid.

Each G-C pair has three hydrogen bonds (5×3=15) and each A-T pair has two (3×2=6). The total is 15+6=21.

Alleles are alternative nucleotide variants of a gene found at the same chromosomal locus, governing variations of the same trait.

To form proper hydrogen bonds across the core, the twin strands must line up in opposite orientations, pairing a 5' end with a 3' end.

A locus refers to the fixed geographic coordinate or position where a gene or genetic marker resides on a chromosome.

Coined by Francis Crick, the Central Dogma outlines the unidirectional transfer of functional sequence information during gene expression.

Lacking a 2'-OH group allows deoxyribose to prefer a C2'-endo sugar pucker, which drives the flexible, uncrowded B-DNA geometry.

An operon is a functional genetic unit found in bacteria that allows several genes in a shared pathway to be transcribed together as a single mRNA.

Heating a DNA sample provides enough thermal energy to break the hydrogen bonds and base-stacking interactions, separating the strands.

A nonsense mutation introduces a premature stop signal (UAA, UAG, or UGA), halting translation and yielding a truncated protein.

The flat base pairs stack horizontally inside the core of the helix, resembling the sequential steps of a spiral staircase.

The non-template strand matches the mRNA transcript sequence exactly (except that DNA has T where RNA has U), earning it the name "coding strand."

The nucleosome is the primary structural unit of chromatin, packing a 147-base-pair segment of DNA around a histone octamer core.

Inserting or deleting a base shifts the triplet reading frame downstream, completely altering the remaining amino acid sequence.

Each phosphate group in the backbone retains a negative charge at physiological pH by releasing a hydrogen ion (H+), acting as an acid.

By convention, the coding strand is written 5' to 3' because the ribosome reads mRNA 5' to 3' to build a protein from its N- to C-terminus.

The B-DNA helix has a pitch of 3.4 nm and a base-pair step of 0.34 nm, accommodating roughly 10 base pairs per full turn.

Exons are the coding segments of a gene that remain in the mature mRNA transcript after splicing, carrying the blueprint for translation.