Dimers are chemical compounds made up of two structurally similar subunits held together by covalent or hydrogen bonds. They are important in biochemistry and medicine, such as in the diagnosis of thrombosis. Examples include water and carboxylic acids, which form stable dimers through hydrogen bonding. However, in DNA, exposure to UV light can cause two subunits to fuse together, creating a dimer and leading to mutations and skin conditions.
A dimer is a chemical compound made up of two monomers, or subunits, that are structurally similar. Two similar molecules bonded together would form a dimer, while many similar molecules bonded together would form a polymer. Dimers are commonly held together by covalent or hydrogen bonds. They are often important in the fields of biochemistry and especially medicine, where they are involved in the diagnosis of certain diseases.
An example of a dimer that is formed through hydrogen bonding is the dimer of water. The water molecule, which consists of two hydrogen atoms and one oxygen atom arranged in a triangular shape, is a polar molecule – in other words, there is a separation of electric charge across its molecular structure. The electrons, which carry a negative charge, are more concentrated at the oxygen end of the molecule than at the hydrogen end. This means that the hydrogen end carries a positive charge, while the oxygen end carries a negative charge. Two water molecules connect through hydrogen bonding when the hydrogen end of one molecule is attracted to the oxygen end of the other.
Carboxylic acids are another type of chemical compound that tends to form stable dimers through hydrogen bonding. These organic acids contain one or more carboxyl groups, a molecular structure made up of carbon, oxygen and hydrogen. Acetic acid, found in vinegar, forms dimers in the crystalline and gaseous state. Carboxylic acids boil at hotter temperatures than water because more energy is required to vaporize their stronger structures.
Dimeric acids, molecules related to carboxylic acids, are important in industrial applications. These substances are created from fatty acids and can be used in adhesives, resins, lubricants and fuel oil. The main component of dimeric acid is stearic acid, which is an organic molecule found in vegetable and animal fat and is also sold commercially for laboratory use.
In medicine, dimers are an important tool for diagnosing thrombosis, a condition in which a blood clot within a vein obstructs circulatory flow. The clot is built on the basis of cross-linked protein fragments, which then break down to reveal an underlying structure known as a D-dimer. Elevated levels of D-dimer in the bloodstream indicate that clots are forming, making the diagnosis of thrombosis likely.
The linkage between structural units can also be a problem in deoxyribonucleic acid (DNA), the molecule that contains a cell’s genetic information. DNA, which is made up of repeating subunits, is vulnerable to damage from ultraviolet (UV) light. Exposure to UV light can cause two subunits of DNA to fuse together through covalent bonds, creating a dimer. This fusion makes it impossible for the cell to process the DNA properly, eventually resulting in mutations and skin conditions including melanoma, a dangerous skin cancer.
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