Biomolecules MCQs for NEET — Chemistry Questions with Answers

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.

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

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.'

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.'

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.

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.'

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.'

I is correct because 'globules unfold and helix get uncoiled' affecting overall folding (tertiary and secondary structures). II is incorrect because the primary structure (amino acid sequence) remains intact. III is incorrect because hydrogen bonds are 'disturbed', not strengthened.

Denaturation is caused by changes in temperature or pH that disturb hydrogen bonds. Maintaining optimum conditions (temperature and pH) is where a protein exhibits its highest activity and is least likely to denature. Extremes of temperature and pH (like strong acids/bases leading to extreme pH) cause denaturation.

The context states: 'The secondary structure of protein refers to the shape in which a long polypeptide chain can exist. These structures arise due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between $C=O$ and $-NH-$ groups of the peptide bond.'