The Structure of DNA
The Form behind the Function
DNA Essentials
Structure determines function.
-
Antiparallel Double Helix
DNA consists of two strands of DNA nucleotides zipped together. These strands run in opposite directions. One strand is known as the "coding" strand, and it stores genetic information much like how letters spell out words and sentences in a book. The other strand is rather like a photographic negative, the opposite or complement of the coding information. The two strands wound together create a molecule that looks a lot like a spiral staircase.
-
Nucleic acid = polymer; nucleotide = monomer
DNA is a polymer. It is made up of monomers strung together. The monomeric form is called a DNA nucleotide. There are four kinds of nucleotides, and they consist of a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases (abbreviated G, A, T, or C). You can think of the language of DNA being written in an alphabet consisting of just these four letters.
-
Sugar-phosphate backbone
Along both sides of the ladder, there is a repeating structure: sugar, phosphate, sugar, phosphate. The sugar on the backbone of DNA is deoxyribose (as opposed to ribose in RNA). This backbone does not change, and as such does not carry information.
-
Nitrogenous bases (GATC)
The rungs of the ladder are made up of 4 different kinds of nitrogenous bases: Guanine, Adenine, Thymine, and Cytosine. Guanine and Adenine are two-ringed purines, while Thymine and Cytosine are single-ringed pyrimidines. The order of these bases along the length of a strand of DNA spell out genes.
-
Major and Minor Grooves
The spiral nature of DNA is related to how it is able to interact with other molecules. Rather than every part of the spiral being identical, there is a pattern of a more open turn (the major groove) followed by a more closed turn (the minor groove) which influences where molecules can reach in and bind.
The meaningful structure
When the insight that DNA could store information was shared amongst biologists, the field of molecular biology was born. It is a truism now, but it wasn't immediately obvious. How could deoxyribonucleic acid—chemically, an acid—be meaningful? It only makes sense when you understand its complex structure.
DNA is a double-helix—it looks like a twisted ladder. Its backbone is made of sugars (deoxyribose) and phosphate groups, and the rungs of the ladder are made from 4 nitrogenous bases: Guanine, Adenine, Thymine, and Cytosine. The order of the “rungs,” or bases, is what determines what the DNA is coding for. Think of it like the order of letters in a word, and the order of words in a sentence. Except in the language of DNA, there are only 4 letters: G, A, T, and C.
DNA is a double-helix—it looks like a twisted ladder. Its backbone is made of sugars (deoxyribose) and phosphate groups, and the rungs of the ladder are made from 4 nitrogenous bases: Guanine, Adenine, Thymine, and Cytosine. The order of the “rungs,” or bases, is what determines what the DNA is coding for. Think of it like the order of letters in a word, and the order of words in a sentence. Except in the language of DNA, there are only 4 letters: G, A, T, and C.
Recommended reading
The definitive text
Campbell's Biology is the standard text used in most first-year college biology courses. Reliably researched and well-written, with clear illustrations.
Related Topic
4 Types of Chemical Bonds in Biology
The bonds essential for life
