DNA Consists Of Two Polynucleotide Strands
- Each strand has a sugar–phosphate backbone with nitrogenous bases projecting inward.
- The strands align side by side, forming a double-stranded structure.
The Antiparallel Arrangement of DNA Strands
- The two DNA strands run in opposite directions.
- One strand runs 5′ to 3′, while the other runs 3′ to 5′.
- This arrangement is called antiparallel.
Drawing the Structure of DNA
- When drawing DNA, show:
- Antiparallel strands: One labeled 5' to 3' and the other 3' to 5'.
- Complementary base pairing: Show A paired with T and C paired with G, connected by hydrogen bonds.
- Sugar-phosphate backbone: Represent the backbone as a continuous chain of alternating sugar and phosphate groups.
- You are not required to draw the helical shape of DNA.
Theory of Knowledge
- Complementary base pairing is universal across all living organisms.
- How does this reflect the shared evolutionary ancestry of life?
- Consider how the universality of DNA connects to the Theory of Knowledge.
Self review
- What does it mean that DNA strands are antiparallel, and how is this shown in diagrams?
- Which bases pair together in DNA, and what bonds hold them together?
- Why is complementary base pairing essential for DNA replication?
