Running in opposite directions while maintaining equal distance apart; parallel but inverted or reversed.
From counter- (opposite) + parallel (from Greek parallelos, 'beside one another'). The prefix counter- inverts the typical meaning of parallel to describe opposite directional flow.
In genetics, DNA strands run counterparallel to each other—one strand goes left-to-right while its partner goes right-to-left—and this exact opposite arrangement is absolutely essential for how DNA copies itself and passes on life.
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