Free Importance of Proteins MCQs with Answers

1. Denaturation of a protein involves

• A. hydrolysis of all its peptide bonds
• B. loss of its three dimensional shape while the amino acid sequence remains intact
• C. a change in its amino acid sequence
• D. conversion of the protein into a carbohydrate

Explanation: Heat, extreme pH, heavy metal ions and alcohol break the weak interactions holding the fold, so the chain unravels and biological activity is lost, but the covalent peptide backbone survives. This is why a boiled egg sets irreversibly without breaking down into amino acids. Hydrolysis of the peptide bonds is digestion, a different process requiring enzymes or prolonged heating with acid.

2. The complete hydrolysis of a protein produces

• A. glucose molecules
• B. fatty acids and glycerol
• C. a mixture of amino acids
• D. urea and ammonia

Explanation: Every peptide bond is broken by boiling with concentrated acid or by protease enzymes, releasing the constituent amino acids, which can then be separated by chromatography or electrophoresis. Glucose comes from the hydrolysis of carbohydrates and fatty acids with glycerol from fats. Urea is a later metabolic product formed when surplus amino acids are deaminated in the liver.

3. Which of the following is NOT a function of proteins in the body?

• A. Acting as enzymes
• B. Transporting oxygen
• C. Providing antibodies for defence
• D. Serving as the main long term energy store

Explanation: The body stores energy as fat and, in the short term, as glycogen, and proteins are broken down for energy only when those stores are exhausted, since doing so sacrifices functional tissue. Enzymes, haemoglobin and antibodies are all proteins, as are hormones such as insulin and structural materials such as collagen. This breadth of function is why protein is an essential part of the diet.

4. The biuret test for proteins gives

• A. a violet colour with copper two ions in alkaline solution
• B. a brick red precipitate
• C. a silver mirror
• D. a blue black colour

Explanation: Copper two ions form a violet complex with the peptide linkages, so the test detects the presence of peptide bonds rather than any particular amino acid and requires at least two of them. A blue black colour with iodine is the test for starch and a brick red precipitate with Fehling's solution indicates a reducing sugar. The ninhydrin test is the alternative for free amino acids.

5. Proteins are essential in the diet mainly because they supply

• A. the fastest source of energy
• B. amino acids for the growth and repair of tissues
• C. essential fatty acids
• D. dietary fibre

Explanation: Digested protein provides the amino acids the body reassembles into its own enzymes, hormones, antibodies and structural tissue, and this cannot be done from carbohydrate or fat. Growing children, pregnant women and patients recovering from injury therefore need more of it. Severe protein deficiency in children causes kwashiorkor even when energy intake is adequate.

6. Which protein is responsible for the transport of oxygen in blood?

• A. collagen
• B. haemoglobin
• C. insulin
• D. keratin

Explanation: Haemoglobin is a globular conjugated protein of four chains, each holding an iron containing haem group that binds one oxygen molecule reversibly. Collagen and keratin are fibrous structural proteins and insulin is a hormone. The variety of these roles is why protein is described as the most versatile class of biological molecule.

7. Which factor would NOT denature a protein?

• A. Boiling
• B. Strong acid
• C. Heavy metal ions
• D. Dissolving it in pure water at room temperature

Explanation: Many proteins dissolve in water without any loss of structure, since water is the medium they normally function in. Heat, extremes of pH, heavy metals, alcohol and vigorous agitation all disrupt the weak interactions holding the fold. Denaturation destroys function while leaving the peptide backbone intact.

8. Insulin is a protein hormone whose function is to

• A. raise blood glucose concentration
• B. lower blood glucose concentration by promoting uptake and storage
• C. digest proteins in the stomach
• D. carry oxygen

Explanation: Secreted by the beta cells of the pancreas, insulin increases the permeability of cells to glucose and stimulates its conversion into glycogen, so blood glucose falls. Glucagon raises it, and the two form a negative feedback pair. Insulin was the first protein to have its full amino acid sequence determined.

9. Collagen is the most abundant protein in the human body and its main role is

• A. catalysing reactions
• B. providing tensile strength in skin, tendon and bone
• C. transporting oxygen
• D. storing genetic information

Explanation: Its triple helix of three chains wound together gives collagen enormous tensile strength, which is why tendons and ligaments resist stretching. Vitamin C is needed for its synthesis, and a deficiency produces the weakened connective tissue of scurvy. Genetic information is stored by nucleic acids rather than proteins.