Practice Questions

Plant cells possess an extracellular, rigid cell wall made primarily of cellulose that protects the cell from mechanical stress and osmotic lysis.

Animal cells lack a cell wall entirely; their outermost living boundary is the selectively permeable phospholipid bilayer known as the plasma membrane.

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

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.

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.