Summary
Adenine pairs with thymine and cytosine with guanine through hydrogen bonds.
In depth
A (purine) pairs with T (pyrimidine) via two hydrogen bonds, and G with C via three. Each pair has the same width, giving a uniform helix. Chargaff's rule says amounts of A equal T and G equals C. In RNA, A pairs with U.
Base pairing also lets RNA fold into structures such as tRNA hairpins.
Base pairing depends on geometry as well as hydrogen bonds: a purine pairs with a pyrimidine so that every pair spans the same 1.1 nm, keeping a regular helix. Tautomers, rare alternative forms of bases, can mispair and cause mutations, as Watson and Crick noted. Stacking interactions between neighbouring bases also contribute substantially to stability.
Base pairing is used in many technologies: PCR primers anneal to templates, microarrays and probes find complementary sequences, CRISPR guide RNAs recognise targets, and DNA origami builds nanostructures. Melting temperature rises with the proportion of G and C.
Remember: in RNA, adenine pairs with uracil, and G can also pair loosely with U (a wobble pair).
Frequently asked questions
What is Base Pairing?
Adenine pairs with thymine and cytosine with guanine through hydrogen bonds.
Which area of biology covers Base Pairing, and how advanced is it?
Base Pairing is one of the 52 topics in Molecular Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Codon, Wobble Hypothesis, Okazaki Fragments.
Can you give an example of Base Pairing?
DNA with high GC content melts at a higher temperature than AT-rich DNA, which is important when designing PCR primers.
What should I learn before Base Pairing?
Base Pairing is a Beginner topic, so no earlier topic is required. Other Beginner topics in Molecular Biology that pair well with it include Central Dogma, DNA Replication, Transcription.
What topics are related to Base Pairing?
The closest topics to Base Pairing are Codon, Wobble Hypothesis, Okazaki Fragments, Promoter. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Base Pairing?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Base Pairing. To practise the whole of Molecular Biology, use the Molecular Biology quiz.
How is Base Pairing different from Codon?
Base Pairing: Adenine pairs with thymine and cytosine with guanine through hydrogen bonds. Codon: A triplet of mRNA bases that codes for one amino acid or a stop signal. Read both side by side and note what each one explains.
How should I study Base Pairing step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Codon and explain the difference aloud. Finally, take the Molecular Biology quiz and come back to this page for any question you miss.