chemistry

Mead acid

Mead acid is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mead acid rather than just read about it. In short: Mead acid is an omega-9 fatty acid, first characterized by James F. Mead.

Key takeaways

Mead acid belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mead acid to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mead acid from memory before moving on to harder problems.

Reference excerpt

Mead acid is an omega-9 fatty acid, first characterized by James F. Mead. As with some other omega-9 polyunsaturated fatty acids, animals can make Mead acid de novo. Its elevated presence in the blood is an indication of essential fatty acid deficiency. Mead acid is found in large quantities in cartilage.

Chemistry Mead acid, also referred to as eicosatrienoic acid, is chemically a carboxylic acid with a 20-carbon chain and three methylene-interrupted cis double bonds, as is typical for polyunsaturated fatty acids. The first double bond is located at the ninth carbon from the omega end. In physiological literature, it is given the name 20:3 (n-9). (See Fatty acid § Nomenclature for an explanation of the naming system.) In the presence of lipoxygenase, cytochrome p450, or cyclooxygenase, mead acid can form various hydroxyeicosatetraenoic acid (HETE) and hydroperoxy (HpETE) products.

Physiology Two fatty acids, linoleic acid and alpha-linolenic acid, are considered essential fatty acids (EFAs) in humans and other mammals. Both are 18 carbon fatty acids unlike mead acid, which has 20 carbons. Linoleic is an ω-6 fatty acid whereas linolenic is ω-3 and mead is ω-9. One study examined patients with intestinal fat malabsorption and suspected EFA deficiency; they were found to have blood-levels of mead acid about 13-fold higher than reference subjects. Under severe conditions of essential fatty acid deprivation, mammals will elongate and desaturate oleic acid to make mead acid, (20:3, n−9). This has been documented to a lesser extent in vegetarians and semi-vegetarians following an unbalanced diet. Mead acid has been found to decrease osteoblastic activity. This may be important in treating conditions where inhibition of bone formation is desired.

Role in inflammation Cyclooxygenases are enzymes known to play a large role in inflammatory processes through oxidation of unsaturated fatty acids, most notably, the formation of prostaglandin H2 from arachidonic acid (AA). AA has the same chain length as Mead acid but an additional ω-6 double bond. When physiological levels of arachidonic acid are low, other unsaturated fatty acids including mead and linoleic acid are oxidized by COX. Cyclooxygenase breaks the bisallylic C-H bond of AA to synthesize prostaglandin H2, but breaks a stronger allylic C-H bond when it encounters Mead acid instead. Mead acid is also converted to leukotrienes C3 and D3. Mead acid is metabolized by 5-lipoxygenase to 5-hydroxyeicosatrienoic acid (5-HETrE) and then by 5-hydroxyeicosanoid dehydrogenase to 5-oxoeicosatrienoic acid (5-oxo-ETrE). 5-Oxo-ETrE is as potent as its arachidonic acid-derived analog, 5-oxo-eicosatetraenoic acid (5-oxo-ETE), in stimulating human blood eosinophils and neutrophils; it presumably does so by binding to the 5-oxo-ETE receptor (OXER1) and therefore may be, like 5-oxo-ETE, a mediator of human allergic and inflammatory reactions.

See also Polyunsaturated fat – lists of ω-3 and ω-6 fatty acids; some others. Eicosanoid Prostaglandin

References

Illustrations

Worked examples

Example 1 — a first encounter with Mead acid

Start with the simplest possible case. Write down what Mead acid claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mead acid before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mead acid ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mead acid

In research: Mead acid appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mead acid in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mead acid is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkenoic acids, Fatty acids, so understanding it makes those chapters shorter.
In everyday life: Look for Mead acid outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mead acid in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mead acid means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mead acid out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mead acid in simple terms?

Mead acid is an omega-9 fatty acid, first characterized by James F. Mead.

Why does Mead acid matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mead acid?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mead acid.