What Are the 4 Types of DNA Monomers?
Deoxyribonucleic acid, or DNA, is the basis for nearly all life forms on Earth. It contains the genetic information that determines the development and functioning of every organism. DNA is composed of four amino acids: adenine, guanine, thymine and cytosine. Each nucleotide, or monomer, has different attributes that allow it to link with the corresponding nucleotide and form a long chain, or sequence.
Adenine is one of the two purines within the nucleotide bases. It consists of two rings -- one with six members, the other with five members -- made of carbon, hydrogen and nitrogen. Purines occur commonly in nature. Caffeine and uric acid are examples of naturally occurring purines. Adenine pairs with thymine in the DNA structure, and it has one other important function: It is the nitrogenous base for adenosine triphosphate, or ATP, which transports chemical energy within cells for metabolism.
Guanine is the other purine nucleotide in DNA. Guanine pairs with cytosine in the DNA structure. Guanine differs from adenine in that it is made up of oxygen in addition to carbon, hydrogen and nitrogen. Like adenine, guanine consists of two rings, one with five members and one with six. Guanine also allows for synthesis of glucose when it is the nitrogenous base for guanosine triphosphate. Guanine may also be used for protein synthesis.
Thymine is a pyrimidine base that binds to adenine in the DNA structure. Instead of the two-ring purine structures, pyrimidine structures have one ring with six members. Thymine is usually replaced with uracil in the RNA structures. Thymine consists of oxygen, hydrogen, nitrogen and carbon. Thymidine triphosphate is used as a "DNA glue." It allows pieces of DNA to stick together to form longer chains, and repair breaks in double strands of DNA.
Cytosine is also a pyrimidine base. It binds to guanine in the DNA structure. Cytosine consists of oxygen, hydrogen, carbon and nitrogen. Like all pyrimidine bases, cytosine has a one-ring structure with six members. Cytosine, like thymine, can be converted to uracil in RNA, and cytosine is the most unstable of the four nucleotides. Because it is unstable, the bond between cytosine and guanine is the bond most easily broken within the DNA strand.
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