All Free Biology MCQs with Answers

2221. Which structural organization is most common in globular proteins____________?

• A. Primary
• B. Secondary
• C. Tertiary
• D. Quaternary

Explanation: Globular proteins usually fold into a compact three-dimensional shape formed by interactions among amino acid side chains, which is their tertiary structure. Secondary structure refers mainly to local alpha helices and beta sheets, while quaternary structure requires multiple polypeptide chains. Students may choose b because alpha helices and beta sheets are visible parts of globular proteins, but they do not describe the complete common organization.

2222. Antibodies play important role against microorganisms and other pathogens to which type of proteins do they belong________?

• A. Globular proteins
• B. Fibrous Proteins
• C. Both a and b
• D. None of these

Explanation: Antibodies are immunoglobulins that recognize antigens and help neutralize or remove pathogens. Their polypeptide chains fold into compact, soluble three-dimensional shapes, so they are classified as globular proteins rather than fibrous structural proteins. Students may choose b because antibodies contain disulphide bonds and have an elongated Y shape, but shape alone does not make them fibrous proteins.

2223. In an aqueous environment the most stable tertiary conformation is that in which _________ amino acids are buried inside the conformation?

• A. Hydrophobic
• B. Hydrophilic
• C. Basic
• D. None of these

Explanation: In water, hydrophobic side chains tend to avoid contact with water and become buried in the interior of a folded protein. Hydrophilic and charged side chains are more likely to remain exposed, where they can interact with water. Students may choose b because hydrophilic amino acids interact well with water, but that is precisely why they are usually exposed rather than buried.

2224. Hemoglobin molecule exhibits which structural organization of proteins___________?

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

Explanation: A haemoglobin molecule is made of four polypeptide subunits, usually two alpha and two beta chains, each containing a haem group. The association of these separate chains gives haemoglobin a quaternary structure. Students may choose c because each individual subunit has tertiary structure, but the complete haemoglobin molecule is described by its quaternary organization.

2225. Which structure of protein gives information aboutnumber and sequence of amino acids in it_______________?

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

Explanation: The primary structure of a protein is the exact number and sequence of its amino acids joined by peptide bonds. Secondary, tertiary and quaternary structures describe folding patterns and subunit associations that arise from this sequence. Students may choose c because the tertiary structure gives the overall three-dimensional shape, but it does not directly specify the amino acid sequence.

2226. Total number of amino acids in a hemoglobin molecule are__________?

• A. 554
• B. 564
• C. 574
• D. 584

Explanation: Adult haemoglobin A has two alpha chains of 141 amino acids each and two beta chains of 146 amino acids each: (2 x 141) + (2 x 146) = 282 + 292 = 574 amino acids. Students often choose 564 by using an incorrect or incomplete chain length instead of adding all four globin chains.

2227. A bond formed by linkage between -OH of carboxyl group of one amino acid and H of amino group of another amino acid which releases water is called__________?

• A. Phosphodiester linkage
• B. Glycosidic bond
• C. Peptide bond
• D. Hydrogen bond

Explanation: A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of another, releasing one molecule of water and producing a C-N linkage. The likely mistake is choosing a hydrogen bond, which is a weak attraction involved in protein shape rather than the covalent bond joining amino acids.

2228. An insulin molecule consists of _________ polypeptide chains?

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: Insulin is a protein made of two polypeptide chains, called the A chain and B chain, joined by disulfide bonds. A common error is choosing one chain because insulin is treated as one hormone molecule, but its molecule contains two separate polypeptide chains.

2229. Proteins are polymers of___________?

• A. Fatty acids
• B. Isoprenoid units
• C. Amino acids
• D. Nucleotides

Explanation: Proteins are polymers whose monomer units are amino acids, joined in chains by peptide bonds. The likely distractor is nucleotides, which are the monomers of nucleic acids such as DNA and RNA, not proteins.

2230. Proteins comprise of ___________% of the total dry weight of a cell?

• A. 40%
• B. 50%
• C. 60%
• D. 70%

Explanation: Proteins make up approximately 50% of the dry mass of a typical cell, reflecting their roles as enzymes, structural materials, transporters and cell machinery. Students may choose 60% by confusing the proportion of protein in some tissues or organisms with the usual cellular dry-weight estimate.