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Limiting Amino Acids
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Why do vegetarians have to be more careful about what they eat than people who include meat in their diet? The raw materials for synthesizing proteins must come from the food we eat. Proteins are composed of long chains of smaller molecules called amino acids. There are 20 amino acids used in protein synthesis. Eight of these 20 molecules are called essential amino acids because humans are incapable of synthesizing them from other compounds. A ninth, histadine, is essential for infants but not for adults. All of the essential amino acids must be obtained directly from food. The non-essential amino acids can be synthesized from organic material that contains a sufficient amount of nitrogen.

Synthesis of proteins therefore depends on a supply of all of the essential amino acids. Animal proteins are generally complete and contain the essential amino acids in appropriate proportions for a healthy diet. Plant proteins are often incomplete and have insufficient quantities of one or more amino acids. A vegetarian diet requires careful selection of foods to ensure all essential amino acids are present in sufficient amounts.

View the animation below, then complete the quiz to test your knowledge of the concept.






1The total amount of protein a person can make will change based on availability of
A)synthesizing amino acids.
B)non-essential amino acids.
C)essential amino acids.
D)building amino acids.



2Tryptophan, methionine, threonine and valine are all
A)essential amino acids.
B)non-essential amino acids.
C)bottom amino acids.
D)sufficient amino acids.



3What happens to protein synthesis when there is a limiting amino acid?
A)protein synthesis increases
B)protein synthesis is limited
C)protein synthesis continues unaffected
D)protein synthesis will only occur in the kidneys



4In the example shown, what happens to protein synthesis when 100% of valine is provided and tryptophan is limiting?
A)protein synthesis is about 100%
B)protein synthesis is about 75%
C)protein synthesis is about 50%
D)protein synthesis is about 25%



5In the example shown, what happens to protein synthesis when 100% of histadine is provided?
A)protein synthesis is about 100%
B)protein synthesis is about 75%
C)protein synthesis is about 50%
D)protein synthesis is about 25%







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