DNA is a very long molecule that codes for the construction of proteins in cells, according to "Molecular Biology of the Cell," by Bruce Alberts. Proteins have many functions, such as helping chemical reactions, communication and structural support. DNA codes for these proteins using different sequences of four bases: adenine, gaunine, cytosine and thymine. Adenine and guanine are chemicals called purines and cytosine and thymine are chemicals called pyrimidines. DNA has two strands, and purines bind to pyrimidines across the strands.
Adenine
Adenine is a purine. It has two rings and binds to thymine in DNA and the base uracil in RNA by two hydrogen bonds. It also is a component of ATP, which is a main source of energy for chemical reactions. It also a component of NAD and FAD, which are chemicals involved in cellular respiration, which extracts energy from oxygen according to "Lehninger Principles of Biochemistry," by Albert L. Lehninger.
Guanine
Guanine is also a purine with two rings. It binds to cytosine across the DNA strands by three hydrogen bonds. Guanine is found in DNA and RNA. When combined with the sugar ribose to be incorporated into DNA, it is called gaunosine. Though not as prevalent as ATP, it can form GTP, which also is used in energy transfer reactions in the cell, and can be used to regenerate ATP.
Cytosine
Cytosine is a pyrimidine that binds to gaunine. Unlike the purines, the pyrimidines have a single ring structure. It is found in DNA and RNA. When phosphates are added to it, it helps enzymes in the process of fat and carbohydrate metabolism.
Thymine
Thymine is a base found in DNA but not RNA. Like cytosine, it is a pyrimidine with a single ring structure. It binds to adenine across the DNA strands. If phosphates are added to this base, it can be used to regenerate ATP to help to restore cellular energy. Thymine is also a target of UV light, which can cause adjacent thymine groups to bind to each other and disrupt the structure of DNA.
References
- "Molecular Biology of the Cell"; Bruce Alberts; 2007
- "Lehninger Principles of Biochemistry"; Albert L. Lehninger, David L. Nelson, and Michael M. Cox; 5th Ed 2008
