All Free Biology MCQs with Answers

4501. Which of the following statements is incorrect about amino acids?

• A. All known α-amino acids possess an asymmetric carbon atom except glycine
• B. Certain antibiotics contain some amino acids in L-isomer form
• C. If an amino acid has more than one asymmetric carbon atom, all the isomers shall be optically active
• D. None of the above

Explanation: Statement C is incorrect.If an amino acid has multiple asymmetric carbon atoms , not all isomers will necessarily be optically active. For an isomer to be optically active, it must have a chiral carbon and lack a plane of symmetry. However, if an amino acid has multiple chiral carbons and possesses a plane of symmetry, some isomers may be meso compounds, which are optically inactive due to internal symmetry.

4502. The formation of phosphodiester bonds between two nucleotides is what kind of process?

• A. Anabolic Process
• B. Catabolic Process
• C. Both anabolic and catabolic
• D. None of the above

Explanation: The formation of phosphodiester bonds between two nucleotides is an anabolic process. Anabolic processes involve the synthesis or building of complex molecules from simpler ones, typically requiring the input of energy. In the case of nucleotides, the formation of phosphodiester bonds occurs during DNA and RNA synthesis, where individual nucleotides are linked together through the formation of phosphodiester bonds. This process requires energy and leads to the formation of longer polynucleotide chains, which are essential for the storage and transmission of genetic information.

4503. What is the basis for the difference in the synthesis of the leading and lagging strands of DNA molecules? The anti-parallel arrangement of the DNA strands. The RNA primers are required to initiate DNA elongation. DNA polymerase joins new nucleotides to the 3' end of the growing strand. Helicase and single-stranded binding proteins work at the 5' end of the DNA strand.

• A. I and IV
• B. I and III
• C. II and IV
• D. II and III

Explanation: The DNA strands are antiparallel i.e. run in opposite directions. Synthesis of new daughter strand by DNA polymerase is only in the 5' to 3' direction, thus the DNA template is read in the 3' 5' direction. This means only the leading strand can be synthesized continuously because the DNA polymerase is moving in the same direction as the unwinding DNA. The lagging strand is synthesized discontinuously, because the DNA polymerase has to move away from the unwinding enzyme in the 5' to 3' direction.

4504. The insulin molecule is composed of two polypeptide chains, one consisting of 20 amino acids and the other consisting of 31.What is the minimum number of base pairs of DNA required to code for this molecule?

• A. 20
• B. 51
• C. 102
• D. 153

Explanation: Each amino acid is coded by a codon of 3 nucleotides bases. Hence, the least number of base pairs 20 x 3 + 31 × 3 = 153.

4505. In double helix of DNA, the two DNA strands are :

• A. Coiled around a common axis
• B. Coiled around each other
• C. Coiled differently
• D. Coiled over protein sheath

Explanation: According to the Watson-­Crick model, the DNA molecule consists of two long, parallel chains which are joined together by short crossbars at regular intervals. The two chains are spirally coiled around a common axis in a regular manner to form a right-handed double helix.

4506. The chitinous exoskeleton of arthropods is formed by the polymerization of:

• A. D-glucosamine
• B. lipo glycans
• C. N - acetyl glucosamine
• D. Keratin sulphate and chondroitin sulphate

Explanation: This is the correct answer. The chitinous exoskeleton of arthropods is formed by the polymerization of N-acetylglucosamine, a derivative of glucose. Chitin is a long-chain polymer of N-acetylglucosamine. Therefore, the correct answer is option C: "N-acetylglucosamine."

4507. DNA is composed of nucleotides and the amino acids are the monomers of proteins. The statement comes from:

• A. Molecular Biology
• B. Microbiology
• C. Biotechnology
• D. Genetics

Explanation: Molecular biology is the branch of biology that deals with the molecular basis of biological activity. The statement about DNA being composed of nucleotides and amino acids being the monomers of proteins aligns with the principles of molecular biology, which explores the structure and function of biological macromolecules. Hence, the correct answer is A because the statement addresses the molecular composition of DNA and proteins, aligning with the key concepts of molecular biology.

4508. Fats containing unsaturated fatty acids are liquid at room temperature because;

• A. All the valencies of carbon are satisfied by single bonds
• B. They contain even number of carbon atoms
• C. Their structure has bends which makes them more fluid
• D. Their structure is chain-like which allows them to be more fluid

Explanation: This statement is the correct explanation for why fats containing unsaturated fatty acids are liquid at room temperature. Unsaturated fatty acids have one or more double bonds in their carbon chain. These double bonds introduce kinks or bends in the structure, preventing the fatty acid molecules from packing closely together. The presence of these bends or kinks makes the fatty acids more fluid, leading to a liquid state at room temperature. The more double bonds present in the fatty acid chain, the more bends or kinks there will be, resulting in a more fluid nature.

4509. What is true about the given structures?

• A. Label C is a glycosidic linkage
• B. Compound A loses OH- ions
• C. Compounds labeled B has Carboxylic functional group
• D. Dehydration synthesis of A and B forms wax

Explanation: B represents fatty acids, which contain the carboxylic acid group (-COOH).

4510. Denaturation of protein;

• A. Disrupts the primary or secondary or tertiary structure of protein
• B. Disrupts the secondary and tertiary structures only
• C. Disrupts all the primary, secondary and tertiary and even the quaternary structure of protein
• D. Will not affect the original biological activity

Explanation: Denaturation can disrupt the secondary and tertiary structures of a protein. The secondary structure refers to the local folding patterns of the protein, such as alpha-helices and beta-sheets, which are stabilized by hydrogen bonds. Denaturation can break these hydrogen bonds, resulting in the loss of secondary structure.