MCQs

Purines are double-ringed; pairing two purines would exceed the 2 nm diameter, while pairing two pyrimidines would make the helix too narrow.

The hydrophilic sugar-phosphate backbones face the aqueous exterior, while the nitrogenous bases point inward to hide from water and form pairs.

Refined by Beadle and Tatum, and later updated to "one gene-one polypeptide," this concept binds a genetic locus to a single protein product.

The glycosidic bonds do not project directly opposite one another, making the spaces between the backbones unequal around the cylinder.

If A=30%, then T=30%, totaling 60%. The remaining 40% is split equally between Guanine (20%) and Cytosine (20%).

While hydrogen bonds hold the pairs together horizontally, vertical base-stacking interactions insulate the hydrophobic bases from water.

The 3' end of a nucleic acid strand terminates at the third carbon of the sugar ring, which carries a free hydroxyl group.

Structural genes carry the specific nucleotide blueprints required to assemble amino acids into a polypeptide chain on a ribosome.

Cytosine and thymine are single-ring pyrimidines, whereas adenine and guanine are double-ring purines.

A codon is a triplet of bases that specifies a particular amino acid or a stop signal during protein translation.

One complete helical turn spans a longitudinal length of 3.4 nm (34 A˚) and contains approximately 10 base pairs.

Chargaff’s rules dictate that [A]=[T] and [G]=[C]; therefore, the sum of purines (A+G) must equal the sum of pyrimidines (T+C).

Rosalind Franklin’s famous "Photo 51" obtained via X-ray crystallography revealed the helical configuration and dimensions of the DNA molecule.

Phosphodiester bonds covalently link the 3' carbon of one deoxyribose sugar to the 5' carbon of the adjacent sugar via a phosphate group.

The double helix maintains a constant width of 2 nm (20 A˚) because a double-ringed purine always pairs with a single-ringed pyrimidine.

Adenine (a purine) always pairs with thymine (a pyrimidine) using two hydrogen bonds in standard Watson-Crick base pairing.

The 5' end of a DNA or RNA strand terminates in a phosphate group attached to the 5' carbon of the pentose sugar.

A gene is the fundamental structural and functional unit of heredity, consisting of a nucleotide sequence that carries the code for a protein.

Guanine pairs with cytosine via three hydrogen bonds, creating a more thermally stable bond than the adenine-thymine pair.