Vitamin K has three forms: K1, K2, and K3. All contain menadione, which aids in blood clotting. K1 and K2 are natural and found in foods, while K3 is synthetic and potentially toxic. The main difference between K1 and K2 is the structure of their side chains.
Vitamin K is an essential vitamin that the body uses in the blood clotting process, and the structure of vitamin K depends on its chemical form. There are three main forms of this vitamin, known as vitamins K1, K2 and K3. K1 and K2 occur naturally and can be found in foods such as spinach, while K3 is a synthetic form. All three of these forms contain a structural component known as menadione, an organic compound containing carbon, hydrogen and oxygen.
The basic structure of vitamin K consists of a menadione complex bonded to a string of atoms known as a side chain. The side chain is made up of hydrogen and carbon atoms and varies in length and shape based on the type of vitamin K. Variations in the side chain cause different forms of vitamin K to behave in different ways, but all forms of the vitamin use the same basic mechanism in aiding proteins in blood clot formation. The menadione, not the side chain, is the functional group, that is, the part of the chemical structure of vitamin K that determines its properties.
The menadione component of the vitamin K structure can be visualized as two closed rings of carbon atoms linked together. Outside the rings, carbon atoms are bonded to hydrogen atoms along with an outer carbon/hydrogen group. Two oxygen atoms are bonded to opposite carbon atoms in one of the rings. The structure contains, altogether, 11 carbon atoms, eight hydrogen atoms and two oxygen atoms. In vitamins K1 and K2, one end of the whole complex is connected to the side chain.
Vitamin K1 is found in leafy greens and other foods such as beans and some types of meat. Chemically, it is also known as phylloquinone. Bacteria in the gut change the structure of vitamin K1 to K2, or menaquinone. The main difference between the two forms is in the structure of the side chain.
Vitamin K3 does not include a side chain but exists only as menadione. As an essential component of the vitamin K structure, menadione, or K3, can be used as a precursor to other forms of the vitamin. For example, the human body is capable of converting K3 to K2. Despite this, the use of vitamin K3 as a dietary supplement is banned in some countries due to its potentially toxic effects.
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