Lipids: essential fatty acids: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Lipids: essential fatty acids

Sample item

A 5-month-old infant on prolonged fat-free parenteral nutrition develops scaly dermatitis, sparse hair and thrombocytopenia. Which nutrient is lacking?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Linoleic acid

Linoleic acid (18:2, omega-6) cannot be synthesised because humans lack desaturases beyond the delta 9 position. It is the precursor of arachidonic acid and eicosanoids and is a component of epidermal ceramides. Deficiency causes scaly skin, hair loss and impaired platelet function; alpha-linolenic acid is the other essential fatty acid.

Option by option

  • A. Palmitic acid

    Palmitic acid is the main product of fatty acid synthase and is not essential.

  • B. Linoleic acid (correct)

    Correct. Linoleic acid is an essential fatty acid whose absence produces this picture.

  • C. Stearic acid

    Stearic acid is formed by elongation of palmitate and is not essential.

  • D. Oleic acid

    Oleic acid is made by delta 9 desaturation of stearic acid, so it is not essential.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Linoleic acid. Linoleic acid (18:2, omega-6) cannot be synthesised because humans lack desaturases beyond the delta 9 position.

Why is "Palmitic acid" not the answer?

Palmitic acid is the main product of fatty acid synthase and is not essential.

Why is "Stearic acid" not the answer?

Stearic acid is formed by elongation of palmitate and is not essential.

Why is "Oleic acid" not the answer?

Oleic acid is made by delta 9 desaturation of stearic acid, so it is not essential.

What concept does this question test?

It tests Lipids: essential fatty acids in Biochemistry. It is the precursor of arachidonic acid and eicosanoids and is a component of epidermal ceramides. Deficiency causes scaly skin, hair loss and impaired platelet function; alpha-linolenic acid is the other essential fatty acid.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Lipids: essential fatty acids?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.