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What is the common consequence of subjecting a native protein to a physical change like increased temperature or a chemical change like altered pH?

A. Formation of new peptide bonds. B. Enhancement of its biological activity. C. Loss of biological activity due to denaturation. D. Strengthening of hydrogen bonds within the protein.

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Explanation

The NCERT states, 'When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of protein.'

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Which of the following events occur during the denaturation of a protein?

A. Peptide bonds are hydrolyzed. B. The polypeptide chain gets shortened. C. Hydrogen bonds are disturbed, leading to unfolding of globules and uncoiling of helices. D. The primary structure is broken down into individual amino acids.

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Explanation

The NCERT text explicitly mentions, 'When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity.'

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Which of the following is an example of protein denaturation?

A. Solubilization of glucose in water. B. Digestion of food by enzymes. C. Coagulation of egg white on boiling. D. Formation of starch from glucose.

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Explanation

The NCERT provides, 'The coagulation of egg white on boiling is a common example of denaturation.'

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Curdling of milk is an example of protein denaturation. What causes this denaturation?

A. Increase in temperature. B. Decrease in fat content. C. Formation of lactic acid by bacteria, leading to a change in pH. D. Exposure to UV radiation.

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Explanation

The NCERT states, 'Another example [of denaturation] is curdling of milk which is caused due to the formation of lactic acid by the bacteria present in milk.' This change in lactic acid affects the pH leading to denaturation.

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What is typically preserved in a protein undergoing denaturation?

A. Tertiary structure only. B. Secondary structure only. C. Quaternary structure only. D. Primary structure.

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Explanation

The NCERT explicitly mentions, 'During denaturation secondary and tertiary structures are destroyed but primary structure remains intact.'

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High temperature destroys enzymatic activity because:

A. The enzyme molecules become saturated with substrate. B. Low temperature preserves the enzyme in an inactive state. C. Proteins are denatured by heat. D. The activation energy of the reaction increases.

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Explanation

From the 'Factors Affecting Enzyme Activity' section, it is stated, 'Low temperature preserves the enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because proteins are denatured by heat.'

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A native protein refers to a protein with:

A. highly flexible and unstructured form. B. unique three-dimensional structure and biological activity. C. Only primary and secondary structures. D. denatured and inactive conformation.

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Explanation

The NCERT defines it as, 'Protein found in a biological system with a unique three-dimensional structure and biological activity is called a native protein.'

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Which level(s) of protein structure is/are directly affected and destroyed during denaturation?

A. Primary structure only. B. Primary and secondary structures. C. Secondary and tertiary structures. D. All four structures (primary, secondary, tertiary, quaternary).

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Explanation

The NCERT text clearly states, 'During denaturation secondary and tertiary structures are destroyed but primary structure remains intact.' If a protein has a quaternary structure, it would also be disrupted as it depends on the tertiary structure of individual subunits.

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What is the primary mechanism by which changes in temperature or pH lead to protein denaturation?

A. Breaking of covalent bonds. B. Disruption of hydrogen bonds. C. Formation of new peptide linkages. D. Alteration of amino acid sequence.

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Explanation

The NCERT explains, 'When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed.'

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Enzymes are almost all globular proteins. How does denaturation affect their catalytic activity?

A. It increases their catalytic efficiency. B. It converts them into fibrous proteins. C. It causes them to lose their biological activity, including catalytic function. D. It alters their substrate specificity but retains activity.

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Explanation

The NCERT states, 'protein loses its biological activity' due to denaturation. Since enzymes are globular proteins and their biological activity is catalysis, denaturation leads to a loss of this function. Also, from the 'BIOMOLECULES_biology' chapter summary, 'Proteinaceous enzymes exhibit substrate specificity, require optimum temperature and pH for maximal activity. They are denatured at high temperatures.'

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