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’s sugar-phosphate backbones carry four kinds of bases. Complementary pairing links A with T and C with G. The sequence on one strand therefore helps determine the aligned sequence on the other. This supports copying. Real strands run in opposite chemical directions, which the end labels in the model make explicit.
The human body · Discover & try
How does DNA pairing help preserve information?
Reading level 3 of 5 · IndependentChange
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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