Nucleotides are the building blocks that form our genetic material, DNA and RNA. These complex molecules determine everything about an individual living thing, from species to shape to color and even some aspects of health. Out of these five basic molecules comes every characteristic of every living creature on earth.
How many nucleotides are there?
There are five basic nucleotides. Four of these, adenine, cytosine, thymine, and guanine, make up the double helix strand of DNA residing in every individual living cell. A fifth, uracil, takes the place of thymine in RNA molecules. The nucleotides line up in what is called a base pair, with adenine and thymine (or uracil) always forming a pair and guanine and cytosine always forming a pair. These base pairs line up in long, complex sequences to form genes and chromosomes.
Structure of nucleotides
Nucleotides are made up of a base called a nucleobase that is bonded to a phosphate and a sugar made of five carbons. These three elements bound together are called a nucleotide. Without the phosphate, the combination of molecules is called a nucleoside.
The nucleobase determines if the nucleotide is adenine, cytosine, thymine, guanine, or uracil. It also allows the base pairs to bond with each other. Adenine and thymine or uracil bond to each other via two hydrogen bonds, while cytosine and guanine bond via three hydrogen bonds. Any other pairing of the nucleotides would make the signature double helix shape of the DNA strand impossible. In fact, the discovery of the exclusive nature of nucleotide bonding into base pairs helped scientists determine the shape of DNA.
The type of sugar in a nucleotide depends upon whether it is part of a DNA or an RNA molecule. The two sugars that make up nucleotides are 2-deoxyribose and ribose. Deoxyribose gives DNA its full name-deoxyribonucleic acid-and RNA, ribonucleic acid, derives its name from ribose.
Classification of nucleotides
Nucleotides are divided into two classes-double-ringed and single-ringed. The double-ringed nucleotides, adenine and guanine, are called purines. The single-ringed nucleotides, cytosine, thymine and uracil, are pyrimidines. These structures are not unique to nucleotides as they are used to categorize other types of molecules as well. For example, caffeine is a purine molecule. However, these structures also help determine base pair bonding since each base pair consists of one purine and one pyrimidine.
What nucleotides do
The order nucleotides line up in a DNA or RNA strand creates a code that tells an organism's cells how to construct proteins. Cells use these proteins to perform everything from building new cells of specific types to assisting in metabolic functions. The proteins built from the codes formed by nucleotides in base pairs are vital to every individual function in every organism on earth.
If parts of the standard DNA chain are missing or duplicated, such as a missing chromosome or too many of a single chromosome, the organism can develop improperly. Downs Syndrome occurs in humans when three copies of chromosome 21 form in the DNA. Missing or malformed pieces of the DNA strand can also cause an organism to be unable to synthesize certain proteins, leading to systemic problems like cystic fibrosis.