biology : class12 Protein Quality : Definition, Sources, Nutritional Importance : Single Cell Protein MCQ Questions and Answers
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Protein Quality
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MCQ Questions
1. A single-cell protein contains 45 mg of lysine per gram of protein, whereas the reference protein requires 55 mg per gram. If all other essential amino acids are present in amounts exceeding reference requirements, what is the approximate chemical score of this SCP protein?
A.
45%
B.
82%
C.
100%
D.
122%
Correct Answer:
82%
Explanation:
The chemical score is calculated from the most limiting essential amino acid: (45/55) × 100, which is approximately 82%. Lysine is therefore the limiting amino acid.
2. Two single-cell protein preparations each contain 60% crude protein. Preparation X has a balanced essential-amino-acid profile and 90% digestibility, whereas preparation Y is deficient in one essential amino acid and has 95% digestibility. Which conclusion is most accurate?
A.
Preparation Y necessarily has the higher biological value because its digestibility is greater
B.
Preparation X may have the higher biological value despite its lower digestibility
C.
Both preparations must have identical protein quality because their crude-protein percentages are equal
D.
Preparation Y has superior protein quality because a limiting amino acid does not affect utilization
Correct Answer:
Preparation X may have the higher biological value despite its lower digestibility
Explanation:
Protein quality depends on both digestibility and the balance of essential amino acids. A deficiency of one essential amino acid can substantially reduce biological value, so the more balanced protein may be utilized better even with slightly lower digestibility.
3. Which change would most directly improve the amino-acid quality of a single-cell protein that is specifically limited by methionine?
A.
Increasing its total carbohydrate content
B.
Adding a complementary protein rich in methionine
C.
Increasing its nucleic-acid concentration
D.
Reducing the amount of digestible protein supplied
Correct Answer:
Adding a complementary protein rich in methionine
Explanation:
Protein complementation improves quality by supplying the essential amino acid that limits utilization. A methionine-rich complementary protein can correct the deficiency and improve the amino-acid balance.
4. A protein sample provides 80% of the reference requirement for lysine, 110% for threonine, 95% for methionine, and 125% for tryptophan. Ignoring digestibility, which value best represents its amino-acid score?
A.
80%
B.
95%
C.
110%
D.
125%
Correct Answer:
80%
Explanation:
The amino-acid score is determined by the lowest ratio among the essential amino acids compared with the reference pattern. Lysine is limiting at 80%, so it determines the score.
5. Why can a microbial protein with a high percentage of crude protein still have relatively poor nutritional quality?
A.
Crude protein percentage directly measures the biological value of the protein
B.
Its essential amino acids may be imbalanced or its protein may be poorly digestible
C.
High crude protein always indicates excessive carbohydrate contamination
D.
Protein quality is determined only by the growth rate of the microorganism
Correct Answer:
Its essential amino acids may be imbalanced or its protein may be poorly digestible
Explanation:
Crude protein measures total nitrogen-derived protein content but does not establish amino-acid balance or digestibility. Both factors influence the nutritional quality of single-cell protein.
6. If an SCP protein has a true digestibility of 80% and an amino-acid score of 75%, which interpretation is most appropriate when a digestibility-corrected score is estimated by multiplying these values?
A.
The corrected score is 60%
B.
The corrected score is 75%
C.
The corrected score is 80%
D.
The corrected score is 155%
Correct Answer:
The corrected score is 60%
Explanation:
Multiplying digestibility by amino-acid score gives 0.80 × 0.75 = 0.60, or 60%. This illustrates that both amino-acid adequacy and digestibility affect overall protein quality.
7. A protein has a high biological value but moderate digestibility. Which statement best explains this combination?
A.
The absorbed amino acids are well balanced for body-protein synthesis, although not all dietary protein is absorbed
B.
Most of the protein is absorbed, but its amino acids are severely imbalanced
C.
Biological value is determined only by total nitrogen content
D.
Moderate digestibility proves that the protein contains no essential amino acids
Correct Answer:
The absorbed amino acids are well balanced for body-protein synthesis, although not all dietary protein is absorbed
Explanation:
Biological value concerns how effectively absorbed amino acids are retained and used for body-protein synthesis. A protein can therefore have good amino-acid balance among absorbed amino acids while having only moderate digestibility.
8. When evaluating the protein quality of a yeast-based single-cell protein, which finding would most strongly indicate a limiting essential amino acid?
A.
The protein contains a high total nitrogen percentage
B.
One essential amino acid occurs at a much lower proportion than in the reference pattern
C.
The culture grows rapidly on an inexpensive substrate
D.
The biomass contains a high proportion of non-protein carbohydrates
Correct Answer:
One essential amino acid occurs at a much lower proportion than in the reference pattern
Explanation:
An essential amino acid is limiting when its proportion is lowest relative to the reference requirement. This shortage restricts the utilization of the other absorbed amino acids for protein synthesis.
9. Two SCP proteins have identical amino-acid scores. Protein P has 92% digestibility, while protein Q has 70% digestibility. Which statement is justified?
A.
Protein Q must have the higher biological value because lower digestibility prevents amino-acid imbalance
B.
Protein P is expected to provide greater usable protein, assuming comparable metabolic utilization
C.
Digestibility cannot influence the nutritional value of microbial proteins
D.
Protein P and Q must provide identical usable protein because their amino-acid scores are equal
Correct Answer:
Protein P is expected to provide greater usable protein, assuming comparable metabolic utilization
Explanation:
With equal amino-acid scores, the protein having higher digestibility generally supplies more absorbable amino acids. Therefore, protein P is expected to have greater usable nutritional value.
10. A researcher improves the digestibility of an SCP preparation but does not alter its essential-amino-acid composition. What is the most direct expected effect on protein quality?
A.
The limiting amino acid will automatically be replaced by a nonessential amino acid
B.
More of the same amino-acid pattern will become available for absorption, although the amino-acid limitation remains
C.
The protein will acquire all essential amino acids in the reference proportions
D.
The total nitrogen content will become irrelevant to protein evaluation
Correct Answer:
More of the same amino-acid pattern will become available for absorption, although the amino-acid limitation remains
Explanation:
Improved digestibility increases the fraction of protein that can be absorbed, but it does not correct an inherent deficiency of a limiting essential amino acid. Amino-acid balance and digestibility are separate components of protein quality.
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