Base pairs, consisting of nucleotides joined by hydrogen bonds, make up DNA and RNA. Adenine (A), thymine (T), cytosine (C), and guanine (G) are the nucleotides that make up an organism’s genetic code. Adenine pairs with thymine, and cytosine pairs with guanine due to their molecular structure. The human genome contains approximately three billion base pairs, which determine the arrangement of genes.
Base pairs are pairs of nucleotides joined with a hydrogen bond present in DNA and RNA. This genetic material is typically double-stranded, with a ladder-like structure, and each set of base pairs constitutes a single rung on the ladder. Base pairs have a number of interesting properties that make them subjects of interest, and understanding how base pairs work is important to many geneticists.
The nucleotides that make up DNA are adenine (A), thymine (T), cytosine (C) and guanine (G). In RNA, thymine is replaced with uracil (U). Together, these tiny chemical compounds make up an organism’s genetic code, with their arrangement coding for the production of a certain number of proteins. Adenine can only bind with thymine and cystosine can only bind with guanine. This means, for example, that when examining a DNA strand, if there’s an A on one end of a peg, a T must be on the other.
Adenine and guanine are both types of molecules known as purines, while thymine and cytosine are pyrimidines. The purines are larger, with a structure that prevents two of them from fitting on a rung of the ladder, while the pyrimidines are too small. This means that adenine cannot become a base pair with guanine and thymine cannot be base pair with cytosine.
One might reasonably ask why the purine adenine cannot bind with the pyrimidine cytosine and why thymine cannot bind with guanine. The answer has to do with the molecular structure of these compounds; adenine cannot form a hydrogen bond with cytosine, just like 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 peg dictating which compound will lie on the other side.
It takes numerous sets of base pairs to form a single gene, and any given strand of DNA can contain numerous genes as well as sections of what is known as “noncoding DNA,” DNA that appears to have no function. The human genome contains approximately three billion base pairs, which explains why it took so long to successfully sequence the human genome, and understanding the arrangement of base pairs doesn’t help people figure out where specific genes are located and what do those geniuses do. In a sense, base pairs could be thought of as the alphabet in which the book of genetic code is written.
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