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Chemical structure of an acetyl group bound to the remainder R of a molecule.

In organic chemistry, acetyl (ethanoyl), is a functional group, the acyl of acetic acid, with chemical formula -COCH₃. It is sometimes abbreviated as Ac (not to be confused with the element actinium). The acetyl radical contains a methyl group single-bonded to a carbonyl. The carbon of the carbonyl has a lone electron available, with which it forms a chemical bond to the remainder R of the molecule.

The acetyl radical is a component of many organic compounds, including the neurotransmitter acetylcholine, and acetyl-CoA, and the analgesics acetaminophen and acetylsalicylic acid (better known as aspirin).

The introduction of an acetyl group into a molecule is called acetylation (or ethanoylation). In biological organisms, acetyl groups are commonly transferred bound to Coenzyme A (CoA), in the form of acetyl-CoA. Acetyl-CoA is an important intermediate both in the biological synthesis and in the breakdown of many organic molecules.

Acetyl groups are also frequently added to histones and other proteins modifying their properties. For example, on the DNA level, Histone acetylation by acetyltransferases (HATs) causes an expansion of chromatin architecture allowing for genetic transcription to take place. Conversely, removal of the acetyl group by histone deacetylases (HDACs) condenses DNA structure, thereby preventing transcription.^[1]

When acetyl groups are bound to certain other organic molecules, they impart an increased ability to cross the blood-brain barrier. This makes the drug reach the brain more quickly, making the drug's effects more intense and increasing the effectiveness of a given dose. Acetyl groups are used to make the natural antiinflammitant salicylic acid into the more effective acetylsalicylic acid, or aspirin. Similarly, they make the natural painkiller morphine into diacetylmorphine, or heroin.

1. ^ North B, Verdin E (2004). "Sirtuins: Sir2-related NAD-dependent protein deacetylases". Genome Biol 5 (5): 224. PMID 15128440. 

• Acetoxy group
• Functional group
• Histone acetylation and deacetylation

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