DNA has paired building blocks called bases. A pairs with T, and C pairs with G. Read across a rung to find a partner. The two strands run in opposite directions, so an aligned partner is different from a strand written in its usual reading direction. DNA sequence information is encoded in nucleotide order, while complementary base pairing constrains the opposite strand: A pairs with T, and C pairs with G. Because the backbones are antiparallel, a sequence read conventionally from its 5′ end differs from a simple left-to-right aligned complement. The flattened, three-base illustration isolates pairing and orientation; cellular replication also requires molecular machinery and many additional steps.
The human body · Discover & try
How does DNA pairing help preserve information?
Reading level 5 of 5 · AdvancedChange
Word help
Base pair
Two complementary DNA bases across the strands.
Complementary
Matching according to the A–T and C–G pairing rules.
Watch · Try · Explain
See how it works
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A flattened three-base model with explicit opposite strand directions. Compare aligned pairing with the direction used to read a strand.
What to look for
- Across the three rungs, the aligned partners are T G C.
- Across these rungs, the aligned partners are A A T.
- The highlighted C pairs with G across the rung.
Explain what you noticed
In an aligned diagram, the top bases read C C A from left to right. Which bases sit directly below them?
Keep this idea: A pairs with T and C with G; strand orientation also matters.
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