Essential amino acids are those that

  • A. are found in every protein
  • B. cannot be synthesised by the body and must be supplied in the diet
  • C. are needed only during childhood
  • D. make up the active site of every enzyme

Explanation

About nine of the twenty amino acids cannot be made by the human body at a useful rate, so they have to come from food, and a protein supplying all of them in good proportion is called a complete protein. Animal proteins are generally complete while most single plant proteins are not, which is why combinations such as rice with pulses matter in a vegetarian diet. All twenty are essential to the cell in the ordinary sense; the term refers only to dietary need.

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