Vitamin K is a group of structurally similar, fat soluble vitamins that are needed for the posttranslational modification

Posttranslational modification

Posttranslational modification is the chemical modification of a protein after its translation. It is one of the later steps in protein biosynthesis, and thus gene expression, for many proteins....

 of certain proteins required for blood coagulation and in metabolic pathways in bone and other tissue. They are 2-methyl-1,4-naphthoquinone (3-)derivatives. This group of vitamins includes two natural vitamer

Vitamer

A vitamer of a particular vitamin is any of a number of chemical substances, each of which shows vitamin activity. Very commonly each "vitamin" is not a single chemical, but rather multiple chemical substances called vitamers, each of which is defined by its different biological activity.For...

s: vitamin K₁ and vitamin K₂.

Vitamin K₁ is also known as vitamin K_j, phylloquinone

Phylloquinone

Phylloquinone is a polycyclic aromatic ketone, based on 2-methyl-1,4-naphthoquinone, with a 3-phytyl substituent.It is a fat-soluble vitamin that is stable to air and moisture but decomposes in sunlight. It is found naturally in a wide variety of green plants.-Terminology:It is often called...

 or phytomenadione (also called phytonadione).
Vitamin K₁ is required for blood coagulation

Coagulation

Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...

 and is synthesized by plants, is found in green leafy vegetables, and can be found in soybean oil.

Vitamin K₂ is involved in bone metabolism.