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== Cysteine ==

'''Cysteine''' (pronounced: sis-teen) is a semi-essential [[amino acid]] that is structurally characterized by its thiol side chain, which often participates in enzymatic reactions and protein conformational structures. 

=== Etymology ===

The term "Cysteine" comes from the Greek word "kystis," meaning bladder. It was so named because it was first isolated from urinary stones in the 19th century.

=== Function ===

Cysteine plays a crucial role in the [[protein]] structure, stability, and function. It is involved in the formation of [[disulfide bond]]s, which are essential for the three-dimensional structure of proteins. Cysteine is also a precursor to the antioxidant [[glutathione]], which protects cells from damage by reactive oxygen species.

=== Dietary Sources ===

Cysteine is found in most high-protein foods, including [[meat]], [[dairy products]], [[eggs]], and some [[grains]] and [[legumes]]. It can also be synthesized in the body from the essential amino acid [[methionine]].

=== Health Implications ===

Cysteine has been studied for its potential health benefits, including its role in detoxification, immune function, and cardiovascular health. However, excessive intake of cysteine can lead to [[cystinuria]], a condition characterized by the abnormal excretion of cystine in the urine, leading to the formation of [[kidney stones]].

=== Related Terms ===

* [[Amino Acid]]
* [[Protein]]
* [[Disulfide Bond]]
* [[Glutathione]]
* [[Methionine]]
* [[Cystinuria]]

[[Category:Amino Acids]]
[[Category:Biochemistry]]
[[Category:Nutrition]]
[[Category:Health]]

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