Biochemistry and biomedical chemistry
DNA and RNA structure
DNA stores information in a paired double helix; RNA shares the nucleotide backbone but often forms diverse single-stranded folds.
IntuitionIntuition: the central idea
DNA stores information in a paired double helix; RNA shares the nucleotide backbone but often forms diverse single-stranded folds.
SchoolSchool level: key concepts and a first application
Definition: Core concept
Antiparallel DNA strands pair A with T and G with C. RNA usually uses uracil instead of thymine; its 2′-hydroxyl group contributes to distinct chemistry and stability.
The sugar–phosphate backbone repeats along each strand; bases project inward to hydrogen-bond across the duplex. A–T pairs use two canonical hydrogen bonds and G–C pairs three.
| Term | Interpretation |
|---|---|
| Base pair | Complementary bases joined by hydrogen bonds across the duplex. |
| Phosphodiester bond | Backbone link joining nucleotides 3′ to 5′. |
| Antiparallel | Strands run 5′→3′ in opposite directions. |
Example: Apply the idea
A DNA duplex contains 18 adenines in one strand. Under canonical pairing, how many thymines occur opposite them?
Solution
There are 18 thymine residues opposite those adenines, because each A pairs with one T. This count does not by itself specify the entire sequence.
UndergraduateUniversity level: quantitative description
Helical geometry can be described by rise per base pair, twist per base pair and groove widths. In canonical B-DNA those values are roughly 3.4 Å, 36°, and a wider major groove than minor groove.
References
- Molecular Biology of the Cell · Bruce Alberts; Alexander Johnson; Julian Lewis; David Morgan; Martin Raff; Keith Roberts; Peter Walter, 2022
- Molecular structure of nucleic acids: a structure for deoxyribose nucleic acid · James D. Watson; Francis H. C. Crick, 1953