Academic journal article The American Biology Teacher

Analogy & Demonstration: Polarity & Antiparallel Orientation in DNA

Academic journal article The American Biology Teacher

Analogy & Demonstration: Polarity & Antiparallel Orientation in DNA

Article excerpt

After learning about the superficial features of DNA structure, including nucleotide components' structures, base pairing rules, and double helical coiling of the complementary strands, introduce your students to the polar nature of a single strand. Knowledge of strand polarity is essential for understanding the processes of replication, transcription, and translation.

Begin by illustrating the conventional scheme for assigning numbers to each of the deoxyrobose sugar's 5 carbon atoms. Show students that a nucleotide's phosphate group attaches to its sugar's 5 prime (5') carbon, while its 3 prime (3') carbon serves as the link connecting the next nucleotide in the chain. Explain that a single DNA strand begins at its 5' end with the phosphate group of the first nucleotide and ends on the last nucleotide's 3' carbon, which is free to connect to the phosphate group of another nucleotide.

[FIGURE 1 OMITTED]

Ask your students to imagine a train consisting of 4 types of railroad cars pulled by an old fashion steam locomotive. This train demonstrates polarity and can be used as an analogy for a DNA strand. The locomotive serves as its 5' end, while the last car on the train, to which additional cars may be added, represents its 3' end. Tell your students that DNA replication involves enzymes, called DNA polymerases, which add additional nucleotides only at the 3' end of the growing strand. …

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