complementary base

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noun Genetics.
either of the nucleotide bases linked by a hydrogen bond on opposite strands of DNA or double-stranded RNA: guanine is the complementary base of cytosine, and adenine is the complementary base of thymine in DNA and of uracil in RNA.
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Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021


What is a complementary base?

A complementary base is either of the two nitrogen-containing sections of a nucleotide that bond together to connect strands of DNA or RNA.

DNA and RNA are complex molecules that are central to genetics and both are made of things called nucleotides. Nucleotides are made of a sugar molecule, phosphoric acid, and a base. In chemistry, the word base refers to a chemical that will give or receive electrons or protons, and the two partner bases that share with each other in the nucleotides of DNA and RNA are called complementary bases.

The arrangement of the complementary bases is crucial to DNA’s structure and is what gives it its characteristic double helix shape.

Why are complementary bases important?

Deoxyribonucleic acid, widely known as DNA, is, essentially, the very complicated molecule that makes you you. In 1949, scientist Erwin Chargaff figured out that DNA always has an equal number of each of the two nitrogen bases that always bond together. We now know these as complementary bases. His observation helped later scientists zero in on the double-helix structure of DNA.

The double helix is shaped like a twisty ladder. Two incredibly long strands of nucleotides form the sides of the ladder. The parts of the nucleotide that connect together to “attach” the two nucleotide strands are called nitrogen bases. In DNA, the nitrogen bases are named guanine, cytosine, adenine, and thymine, and they will connect with each other by forming bonds (specifically, hydrogen bonds) with their hydrogen atoms. Guanine always bonds with cytosine, which makes them a pair of complementary bases. Adenine always bonds with thymine, making them DNA’s other pair of complementary bases. These pairs form the “rungs” of the DNA ladder. (In double-stranded RNA, the four nitrogen bases and their pairings are the same as in DNA except for thymine, which in RNA is replaced by uracil.)

DNA owes its double-helix structure to the complementary bases that form its rungs, but just as important is the order in which these bases are configured. In fact, the order of DNA’s complementary bases is what makes up the genetic code, which is the source of information that cells use to make proteins. And proteins are essential to life itself.

Did you know ... ?

A human being’s DNA is made of pairs of around 3 billion complementary bases, over 99 percent of which is in the same order in all people. In identical twins, the sequence of their complementary bases might have only a few dozen differences out of the entire 3 billion!

What are real-life examples of complementary bases?

Complementary bases are typically one of the first things biology students learn about when studying DNA, since they are crucial to its structure.


What other words are related to complementary base?

Quiz yourself!

Which of the following complementary bases is paired with thymine?

A. uracil
B. adenine
C. guanine
D. cytosine

How to use complementary base in a sentence