Fatty acid
Michel Eugène Chevreul introduced the concept of fatty acid in 1813. He initially used terms like graisse acide and acide huileux to describe these oily acids. The phrase meant acid fat or oily acid in French. This early terminology evolved over time into the modern scientific name we use today. Scientists later standardized the definition to include any carboxylic acid with an aliphatic chain. Most naturally occurring examples contain unbranched chains with even numbers of carbon atoms ranging from four to twenty-eight. These molecules form a major component of lipids in microalgae and other species. They exist as triglycerides, phospholipids, or cholesteryl esters rather than standalone forms in many organisms.
Chemists categorize fatty acids by counting their carbon atoms and checking for double bonds. Short-chain fatty acids possess tails of five carbons or fewer such as butyric acid. Medium-chain variants range from six to twelve carbons while long-chain types span thirteen to twenty-one. Very long chains extend beyond twenty-two carbons including arachidic acid which contains twenty carbons. Saturated versions lack C=C double bonds entirely and follow the formula CH(CH)COOH where n is a positive integer. Stearic acid serves as an important saturated example with sixteen carbons that becomes soap when neutralized with sodium hydroxide. Unsaturated acids feature one or more double bonds creating cis or trans configurations. Cis bonds cause the molecular chain to bend sharply unlike straight saturated structures. Oleic acid displays a single kink while linoleic acid bends further due to two double bonds. Alpha-linolenic acid hooks into shape because it holds three double bonds within its structure.
Animals synthesize fatty acids primarily from carbohydrates inside the liver adipose tissue and mammary glands during lactation. Glycolysis converts carbohydrates into pyruvate before decarboxylation forms acetyl-CoA in the mitochondrion. This acetyl CoA must travel across the inner mitochondrial membrane into the cytosol for synthesis. Citrate carries acetyl-CoA out of the citric acid cycle and splits via ATP citrate lyase. Acetyl-CoA carboxylase then carboxylates the molecule into malonyl-CoA marking the first committed step. A repeating series adds two carbons at a time to lengthen the growing chain. Almost all natural fatty acids end up with even numbers of carbon atoms. Free fatty acids circulate bound to plasma albumin after triglycerides break down through lipolysis. Cells take these molecules up except those in the central nervous system which cannot cross the blood-brain barrier. These cells manufacture their own fatty acids from carbohydrates to maintain phospholipid bilayers in organelles like the nucleus and mitochondria.
Humans require essential fatty acids that cannot be made sufficiently from other substrates so they must come from food. Linoleic acid and alpha-linolenic acid represent two critical examples widely distributed in plant oils. The body lacks ability to introduce double bonds beyond carbons nine and ten when counting from the carboxylic acid side. Alpha-linolenic acid converts partially into longer-chain omega-3 fatty acids including eicosapentaenoic acid and docosahexaenoic acid found in fish. Omega-3 and omega-6 fatty acids serve as biosynthetic precursors to endocannabinoids with antinociceptive properties. Skin barriers form water-impermeable layers using free fatty acids mixed with ceramides and cholesterol. Saturated fatty acids sixteen and eighteen carbons long dominate the epidermis while unsaturated types vary by body site. Psoriasis and atopic dermatitis show characteristic alterations in epidermal fatty acid abundance. Short and medium-chain fatty acids absorb directly into intestinal capillaries traveling through the portal vein. Long-chain fatty acids reassemble into triglycerides inside villi walls before entering lymphatic vessels via lacteals.
Fatty acids produce soap through neutralization reactions known as saponification using metallic hydroxides like sodium hydroxide. Transesterification converts fats into fatty acid methyl esters used for biodiesel production. Hydrogenation treats unsaturated fatty acids under pressure of 2.0 to 3.0 MPa hydrogen gas at 150 degrees Celsius. Nickel supported on silica acts as a catalyst during this hardening process that creates saturated fatty acids. Partial hydrogenation can isomerize cis bonds into trans configurations creating trans fats found in margarine. Decarboxylation produces symmetrical ketones from carboxylic acids using magnesium stearate heating methods. Scientists prepare polyurethane coatings from bio-based dimer acids derived from oleic acid. Fatty alcohols form precursors to surfactants detergents and lubricants through vinyl acetate transesterification. These derivatives function as emulsifiers texturizing agents wetting agents anti-foam agents or stabilizing agents in industrial applications.
Up Next
Continue Browsing
Common questions
When did Michel Eugène Chevreul introduce the concept of fatty acid?
Michel Eugène Chevreul introduced the concept of fatty acid in 1813. He initially used terms like graisse acide and acide huileux to describe these oily acids before the terminology evolved into modern scientific names.
What is the definition of a fatty acid according to scientists?
Scientists later standardized the definition to include any carboxylic acid with an aliphatic chain. Most naturally occurring examples contain unbranched chains with even numbers of carbon atoms ranging from four to twenty-eight.
How are fatty acids categorized by chemists based on their structure?
Chemists categorize fatty acids by counting their carbon atoms and checking for double bonds. Short-chain fatty acids possess tails of five carbons or fewer while medium-chain variants range from six to twelve carbons and long-chain types span thirteen to twenty-one.
Where do animals synthesize fatty acids primarily inside the body?
Animals synthesize fatty acids primarily from carbohydrates inside the liver adipose tissue and mammary glands during lactation. This process involves glycolysis converting carbohydrates into pyruvate before decarboxylation forms acetyl-CoA in the mitochondrion.
Which essential fatty acids must humans obtain from food sources?
Humans require essential fatty acids that cannot be made sufficiently from other substrates so they must come from food. Linoleic acid and alpha-linolenic acid represent two critical examples widely distributed in plant oils.