Free Biological Molecules MCQs with Answers

71. The enzyme that digests starch in the mouth is

• A. Pepsin
• B. Trypsin
• C. Salivary amylase
• D. Lipase

Explanation: Salivary amylase (ptyalin) begins starch digestion in the mouth, breaking it into maltose.

72. Which of the following has the highest energy content per gram?

• A. Carbohydrate
• B. Protein
• C. Lipid
• D. Nucleic acid

Explanation: Lipids provide about 9 kcal/g, while carbohydrates and proteins provide about 4 kcal/g each.

73. DNA and RNA differ in all EXCEPT

• A. Type of sugar
• B. Presence of uracil vs thymine
• C. Being nucleic acids
• D. Single vs double stranded

Explanation: Both DNA and RNA are nucleic acids. They differ in sugar (deoxyribose vs ribose), bases (T vs U), and structure (double vs single stranded).

74. The structure of DNA was discovered by

• A. Franklin and Wilkins
• B. Watson and Crick
• C. Mendel
• D. Avery

Explanation: Watson and Crick proposed the double helix model in 1953, based on Franklin's X-ray diffraction data.

75. DNA replication is

• A. Conservative
• B. Semi-conservative
• C. Dispersive
• D. Non-conservative

Explanation: Meselson and Stahl proved DNA replication is semi-conservative: each new DNA has one old and one new strand.

76. The enzyme that unwinds DNA during replication is

• A. DNA polymerase
• B. Helicase
• C. Ligase
• D. Primase

Explanation: Helicase breaks hydrogen bonds between base pairs, unwinding the DNA double helix.

77. Okazaki fragments are formed on the

• A. Leading strand
• B. Lagging strand
• C. Both strands equally
• D. Neither strand

Explanation: The lagging strand is synthesized discontinuously as Okazaki fragments because DNA polymerase only works 5'→3'.

78. Transcription produces

• A. A DNA copy of DNA
• B. An RNA copy of DNA
• C. A protein from DNA
• D. A DNA copy of RNA

Explanation: Transcription is the synthesis of RNA using DNA as a template, catalyzed by RNA polymerase.

79. The start codon is

• A. UAA
• B. AUG
• C. UAG
• D. UGA

Explanation: AUG codes for methionine and serves as the start codon, initiating protein synthesis.

80. Introns are

• A. Coding sequences
• B. Non-coding sequences removed during splicing
• C. Found only in prokaryotes
• D. Essential for translation

Explanation: Introns are non-coding intervening sequences removed during RNA splicing; exons are joined together.