Nucleotide

Nucleotides are present in almost every cell of an organism. A combination of four of the most prominent nucleotides, Adenosine triphosphate, Guanosine triphosphate, Cytidine triphosphate, and Thymidine triphosphate make up our DNA chain. This is their most prominent use, but there are far more uses for them. In all, there are a total of thirty different nucleotides: fifteen deoxyribonucleotides and fifteen ribonucleotides.[1]

Nucleotides are usually abbreviated; Adenosine triphosphate would be shortened to ATP. The “A” in ATP refers to its nucleobase Adenine. The “T” defines the length of the phosphate group. It can be either “M” for mono- (meaning one), “D” for Di- (meaning two), or “T” as in ATP for Tri- (meaning three). The “P” refers to the fact that it has a Phosphate group. In some cases it will have a lower case “d” in front of the name meaning that it is a deoxyribonucleotide. When it has no “d” in front of it, it means that it is a ribonucleotide. An example of a deoxyribonucleotide is dCTP meaning, deoxy-cytidine-triphosphate. There are also “c” that are placed in front of some nucleotides. An example is cAMP called cyclic-adenosine-monophosphate.[2]

Common Structures

Nucleotides have a rather simple structure. It is the adding together of phosphate groups and other nucleotides that make them able to do their jobs. Nucleotides are a chemical compound composed of sugars a heterocyclic base and a phosphate group. The phosphate groups will either be a mono-, Di-, or Tri-phosphate.

        O   O   O
        ||  ||  ||
      O–P–O–P–O–P–O– 
        |   |   |
        O-  O-  O- 

There are two types of sugars used in nucleotides. Deoxyribose and ribose are the sugars used in the nucleotides. These sugars are Pentose. Pentose is any sugar with five carbons in its string.[3] The main sugars in this group are ribose, arabinose, xylose and lyxose. Out of these four the only one used is ribose.[4]

The last thing that makes up a nucleotide is its heterocyclic base. The most common heterocyclic bases used in nucleotides are purine or pyrimidine. Purine’s chemical formula is C₅H₄N₄, similarly pyrimidine's chemical formula is C₄H₄N₂. The difference between the two is minor. The pyrimidine has one less carbon atom and two less nitrogen atoms. Besides those subtle structural differences they are practically the same.[5]

When these three components are put together they make a nucleotide. The different nucleotides arise when different lengths of phosphate groups mix with the different types of heterocyclic bases and the different sugars. When the nucleotides have no phosphate group they are called nucleosides.(Purves, 54)

Uses for Nucleotides

The most important use for a nucleotide is in DNA and RNA. In DNA when ATP, GTP, CTP and TTP link together they make a long string of information. DNA in essences is pure information. The way the information is coded is in the way the nucleotides align themselves. The string TCAG is very different from the string CCAG. What further makes the DNA complex is that A, T, G and C can not all connect across from each other. The string TCAG and CCAG in DNA would look like the following.[6]

        T-A         C-G
        C-G         C-G
        A-T         A-T
        G-C         G-C

As shown above, T can only bind to A and vice versa. Continuing on, C only to G. This makes DNA strands more complex but also easier to read because if you see one side, you will automatically know what goes on the other side.[7]

RNA is very similar to DNA. There are however so slight changes made to the stands when it is brought out of the nucleus.[8] All of the TTP nucleotides are changed when the DNA sends out RNA. They are changed from Thymine-Triphosphate to Uracil-Triphosphate. So In the DNA strand above TCAG, the RNA strand would change to UCAG. The same A to T pairing would continue though. Instead however to “T” it would pair with “U”. This method of pairing in DNA and RNA is called base pairing.[9]

Other Specific Roles

Nucleotides can have more than one job. Just like one protein can be responsible for constructing hundreds of different proteins. ATP is not only used in DNA, neither is GTP. ATP is also used as a transducer in biochemical reactions. In some reactions ATP can be used to help molecule change its shape. In these cases it works as a catalyst. GTP is a great source of energy. It is sometimes broken down when the cell/molecule needs more energy to perform specific tasks. One such task is protein synthesis. GTP is used in the process to “fuel” the operation. If there were no GTP the synthesizing would have to stop until they could scrounge up other forms of energy such as carbohydrates or free sugars. (Purves, 57)

Another specific role of a nucleotide is performed by cAMP, cyclic-adenosine-monophosphate. This nucleotide is used primarily for sending information. It is important in the actions of hormones. It helps give the hormone the right message to send. It also plays a role in the sending of information through the nervous system. (Purves, 57)

Conclusion

Nucleotide’s primary use is in DNA and RNA. They are what help keep you unique and also what store all the information your body or any organism needs to stay alive. Although nucleotides are simple in nature, they pack a lot of “punch”. Just with alternating four nucleotides in a strand of DNA can hold tons of information, more than computers of our day can hold. Nucleotides are very small by they are vitally important to life and the way things run in the body.

References

• Nucleotides Wikipedia
• Purves, William K. et al. Life: The Science of Biology. Gordonsville, VA. 2004.
• Nucleotides by John W. Kimball