DNA contains base pairs of nucleotides.
Base pairs are pairs of nucleotides linked by a hydrogen bond found in DNA and RNA. This genetic material is typically double-stranded, with a ladder-like structure, with each set of base pairs forming a single rung of the ladder. Base pairs have a number of interesting properties that make them interesting topics, and understanding how base pairs work is important to many geneticists.
Adenine and thymine form a base pair in DNA, as do cytosine and guanine.
The nucleotides that make up DNA are adenine (A), thymine (T), cytosine (C), and guanine (G). In RNA, thymine is replaced by uracil (U). Together, these tiny chemical compounds make up the genetic code of an organism, and their arrangement codes for the production of various proteins. Adenine can only bind to thymine and cystosine can only bind to guanine. This means, for example, that when examining a DNA strand, if there is an A at one end of one step, a T must be at the other.
Base pairs are pairs of nucleotides linked by a hydrogen bond found in DNA and RNA.
Adenine and guanine are types of molecules known as purines, while thymine and cytosine are pyrimidines. Purines are larger, with a structure that prevents two of them from fitting on one rung of the ladder, while pyrimidines are very small. This means that adenine cannot base pair with guanine and thymine cannot base pair with cytosine.
One might reasonably wonder why the purine adenine cannot bind to the pyrimidine cytosine and why thymine cannot bind to guanine. The answer has to do with the molecular structure of these compounds; adenine cannot form a hydrogen bond with cytosine, just as thymine cannot form a hydrogen bond with guanine. These properties dictate the fundamental arrangement of the base pairs, with the compound on one end of the rung dictating which compound will be on the other side.
Several sets of base pairs are needed to form a single gene, and any single strand of DNA can contain multiple genes as well as sections of what is known as “non-coding DNA,” DNA that appears to have no function. The human genome contains about three billion base pairs, which explains why it took so long to sequence the human genome, and understanding the arrangement of base pairs doesn’t help people understand where specific genes are and what. those genes make. In a way, base pairs can be considered the alphabet used to write the genetic code book.