Proteins are classified as ‘complete’ and ‘incomplete’ based on:

Question

BlackTom AI · Accepted Answer

Complete proteins contain all nine essential amino acids in proportions adequate for human requirements, while incomplete proteins lack one or more of these essential amino acids.

1. Relevant knowledge points and concepts
- Essential amino acids are those humans cannot synthesize and must obtain from diet (commonly nine: histidine, isoleucine, leucine, lysine, methionine + cysteine, phenylalanine + tyrosine, threonine, tryptophan, valine).
- Protein “completeness” refers to amino acid profile (presence and proportion of essential amino acids).
- Examples: most animal proteins (eggs, meat, dairy, fish) are complete; many single plant sources (beans, grains, nuts) are often incomplete but can be combined to supply all essentials (complementary proteins).
- Measures of protein quality (PDCAAS, DIAAS) incorporate digestibility and amino acid profile but the basic complete/incomplete label is about amino acid composition.

2. Step-by-step reasoning
- Identify the classification criterion: completeness concerns whether all essential amino acids are present in sufficient amounts.
- Check alternate meanings: “ability to denature and coagulate” is a physical behavior unrelated to amino acid composition; “ability to dissolve completely” is solubility and not a nutritional classification; “ability of humans to completely digest them” refers to digestibility, which affects quality but is not the basis for the complete/incomplete nomenclature.
- Conclude the correct criterion is presence of all essential amino acids.

3. Calculations
- None required for this conceptual question. (If quantifying, one would compare amino acid amounts to human requirements to identify limiting amino acids.)

4. Why the correct answer is correct
- The term “complete protein” is defined nutritionally by containing adequate amounts of all essential amino acids for human maintenance and growth. That definition directly matches the provided option.

5. Why other options are incorrect
- “Ability to denature and coagulate”: describes thermal/chemical behavior, not amino acid completeness.
- “Ability of humans to completely digest them”: digestibility affects protein quality but is a separate concept from completeness.
- “Ability to dissolve completely in a solvent”: solubility is a chemical property unrelated to essential amino acid content.

6. Conclusion
The correct answer is “Whether they contain all the essential amino acids necessary for humans,” which matches the provided answer.

Proteins are classified as ‘complete’ and ‘incomplete’ based on:单项选择题

类似问题

Why is it important for essential amino acids lost from the body to be replaced by the diet?

Which of the following are essential amino acids for infants?

Why is it important for essential amino acids lost from the body to be replaced by the diet?

An incomplete protein is a protein which is missing one or more essential amino acids.

Which amino acid is considered to be essential for animals?

The body can manufacture essential amino acids, so they do not need to be consumed in the diet.

Which of the following is not an essential amino acid?

In addition to the ten dietary essential amino acids required by mammals, birds also require prolamin and glycine.

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