Many of the chemicals in the body are created through what is called a biological pathway. A pathway first requires a precursor molecule, usually from the diet. Then it is progressively modified by a series of enzymes until it reaches a final molecule that can be utilized by living organisms. In this way tyrosine can be changed to become dopamine in the brain.
Features
Tyrosine is a type of amino acid. There are 20 amino acids total, but about nine of them cannot be manufactured by the body and must be obtained through the diet. These are known as essential amino acids. According to the University of Maryland Medical Center, tyrosine is one of the non-essential amino acids: although it can be found in protein-rich foods such as poultry, seafood, nuts, dairy and seeds, it is also synthesized from the amino acid phenylalanine in the body. It is sometimes called L-tyrosine because amino acids on Earth tend to be "left-handed" rather than facing right, which describes the way the side chain on amino acids face.
Function
Tyrosine is involved in the synthesis of dopamine, an important neurotransmitter---a chemical that transmits signals between neurons---involved in motor functions and mood. It is a molecule that aids in attention and learning, activated in response to humor, social interaction and food. However, it also has a dark side: dopamine responds to drugs such as heroine, alcohol, cocaine, nicotine and amphetamines.
Conversion
Tyrosine is metabolized directly to dopamine through a special pathway in the cells. This is accomplished through the enzyme known as tyrosine hydroxylase. An enzyme is a protein that facilitates a chemical reaction. In this case tyrosine hydroxylase is an iron-containing enzyme that transfers oxygen from the air to the tyrosine molecule.
L-Dopa
Tyrosine hydroxylase catalyzes the conversion of L-tyrosine to an intermediate molecule known as L-dopa. To accomplish this task, tyrosine hydroxylase needs a cofactor---a non-protein chemical compound that is bound to the protein to facilitate the biological activity. L-dopa is an organic compound similar in composition to tyrosine. It can also be isolated and used in the treatment of various diseases such as Parkinson's disease.
Significance
Dopamine is finally catalyzed through another enzyme that releases carbon dioxide from L-dopa. Dopamine is a type of catecholamine---essentially, a "fight or flight" hormone released by the adrenal gland in response to stress. Noradrenaline and adrenaline are fellow catecholamine, both of which dopamine can be used to synthesize.
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