Base pairing is the specific hydrogen-bonded matching of complementary nitrogenous bases in nucleic acids: adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C) in DNA, with uracil replacing thymine in RNA.
Base pairing is the rule that controls how the two strands of DNA stick together. Adenine (A) always bonds with thymine (T), and guanine (G) always bonds with cytosine (C). These are the only matches that fit, which is why they're called complementary bases. The bonds holding the pairs together are hydrogen bonds, which are weak individually but add up across millions of base pairs to keep the double helix stable.
Under CED objective AP Bio 1.6.A, you describe the structure of DNA and RNA, and base pairing is the part that explains why DNA can store and copy information. Because A only goes with T and G only goes with C, one strand is the perfect template for rebuilding the other. RNA follows the same idea with one swap: uracil (U) takes thymine's place, so A pairs with U in RNA. Notice that A-T pairs share two hydrogen bonds while G-C pairs share three. That extra bond matters more than it sounds, as you'll see on the exam.
Base pairing lives in Unit 1: Chemistry of Life, topic 1.6 Nucleic Acids, and supports learning objective AP Bio 1.6.A on the structure and function of DNA and RNA. It's the bridge between structure and function: the chemical specificity of the pairs is exactly what lets DNA carry a code, copy itself, and be transcribed into RNA. Almost every later topic about heredity and gene expression quietly depends on this one rule, so locking it in early pays off across the whole course.
Keep studying AP Biology Unit 1
Hydrogen Bonds (Unit 1)
Base pairs are held together by hydrogen bonds, not the strong covalent bonds in the backbone. A-T uses two, G-C uses three, so a DNA sample rich in G-C takes more heat to pull apart. That's the structural reason behind 'denatures at a lower temperature' questions.
Nucleotide (Unit 1)
The nitrogenous base is one of the three parts of a nucleotide (sugar, phosphate, base). Base pairing is just two of those bases meeting across the helix, so understanding the monomer makes the pairing rule obvious.
DNA Molecule (Unit 1)
Base pairing is what makes the two strands of the DNA molecule antiparallel and complementary. Knowing the pairing rule lets you read one strand and instantly write its partner.
Messenger RNA (mRNA) (Unit 1)
When DNA is transcribed into mRNA, base pairing still applies, but RNA uses uracil instead of thymine, so A in DNA pairs with U in the new RNA strand. Same logic, one substituted base.
Multiple-choice stems love to test base pairing through Chargaff-style data. If a sample has equal amounts of A and T and equal amounts of G and C, that's the signature of a double-stranded, base-paired molecule. Expect denaturation questions too: a nucleic acid that melts at a lower temperature than expected usually has more A-T pairs, because those only have two hydrogen bonds instead of three. You should be able to take a given strand sequence and write its complement, swap thymine for uracil when the product is RNA, and explain that hydrogen bonds (not covalent bonds) join the bases while covalent bonds build the backbone. No released FRQ uses 'base pairing' verbatim, but the concept underpins any free-response answer about DNA replication fidelity or transcription accuracy.
Base pairs across the two strands are joined by hydrogen bonds, which are weak and easy to separate (that's how the strands can unzip for replication). The sugar-phosphate backbone along each strand is held by strong covalent bonds. Mixing these up leads to wrong answers about why DNA denatures and how strands separate without breaking apart.
In DNA, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C); in RNA, uracil replaces thymine so adenine pairs with uracil (A-U).
Base pairs are held by hydrogen bonds, which are weak individually but strong together, while the backbone uses covalent bonds.
A-T pairs have two hydrogen bonds and G-C pairs have three, so G-C-rich DNA is harder to denature with heat.
Because pairing is complementary, one strand always serves as a template to rebuild or copy the other.
Equal amounts of A and T plus equal amounts of G and C signal a double-stranded, base-paired nucleic acid (Chargaff's rules).
Base pairing is the rule that complementary nitrogenous bases bond together in nucleic acids: A with T and G with C in DNA, held by hydrogen bonds. It falls under topic 1.6 and objective AP Bio 1.6.A on DNA and RNA structure.
Yes, in DNA adenine always pairs with thymine. But in RNA there's no thymine, so adenine pairs with uracil instead. The G-C pairing stays the same in both.
Because G-C pairs share three hydrogen bonds while A-T pairs share only two. More hydrogen bonds means more energy (heat) is needed to pull the strands apart, so high G-C content raises the melting temperature.
Base pairs across strands are joined by weak hydrogen bonds, which lets the strands unzip during replication. The backbone of each strand is held together by strong covalent bonds between sugars and phosphates.
Chargaff's rules say a double-stranded DNA sample has equal amounts of A and T, and equal amounts of G and C. That's a direct result of base pairing, since every A is matched to a T and every G to a C, so finding those equal ratios tells you the molecule is base-paired and double-stranded.