A purine base with a double-ring structure. Forms two hydrogen bonds with Thymine. Found in ATP — the energy currency of every living cell.
C₅H₅N₅
T
Thymine
PAIRS WITH → A
A pyrimidine base with a single-ring structure. Forms two hydrogen bonds with Adenine. Unique to DNA — replaced by Uracil in RNA.
C₅H₆N₂O₂
G
Guanine
PAIRS WITH → C
A purine base. Forms three hydrogen bonds with Cytosine — the strongest pairing in DNA. High GC content makes DNA more heat-resistant.
C₅H₅N₅O
C
Cytosine
PAIRS WITH → G
A pyrimidine base. Forms three hydrogen bonds with Guanine. Cytosine can spontaneously deaminate — one of the most common sources of DNA mutation.
C₄H₅N₃O
CLICK ANY BASE TO VISUALIZE ITS 3D MOLECULAR STRUCTURE IN TIER II
A·T
Double Helix · 12 Base Pairs
SCIENTIFIC CONFIDENCE
99 %
CRYSTALLOGRAPHY · X-RAY VERIFIED
● ADENINE
● THYMINE
● GUANINE
● CYTOSINE
— BACKBONE
~ H-BOND
DRAG TO SPIN · SCROLL TO ZOOM
1 nm
ONE BASE PAIR = 0.34 nm
DNA REPLICATION · SEMI-CONSERVATIVE MODEL · WATSON-CRICK 1953
REPLICATION SUMMARY
ENZYME HELICASE → POLYMERASE
DIRECTION 5′ → 3′
FIDELITY 1 error / 10⁹ bases
SPEED ~1,000 bp / sec
Each strand serves as a template. The result is two identical double helices — each containing one original strand and one newly synthesized strand. This is semi-conservative replication.
TIER III PREVIEW
Full replication: helicase unwinding, primase, leading and lagging strand synthesis, Okazaki fragments.