Free Biological Molecules MCQs with Answers

91. Which of the following types of RNA makeup the largest proportion of total cellular RNA?

• A. Messenger RNA
• B. Ribosomal RNA
• C. Transfer RNA
• D. Catalytic RNA (ribozyme)

Explanation: Ribosomal RNA accounts for roughly 80 per cent of the RNA in a cell, because every ribosome is built largely from it and a busy cell contains millions of ribosomes. Transfer RNA comes next at around 15 per cent, and messenger RNA is a small and rapidly turning over fraction. Ribozymes are rarer still.

92. Which one of the following biomolecules is a polymer/polysaccharide?

• A. Sucrose
• B. Pentose
• C. Lactose
• D. Glycogen

Explanation: Glycogen is a highly branched polymer of thousands of glucose units, stored in liver and muscle as the animal energy reserve. Sucrose and lactose are disaccharides of just two units and pentose is a single five carbon sugar, so none of them is a polymer. The test is whether the molecule can be hydrolysed into many repeating units.

93. Peptide bonds are important in protein because they:

• A. Affect solubility
• B. Hold R-groups
• C. Link amino acid
• D. Help in releasing oxygen

Explanation: A peptide bond forms by condensation between the carboxyl group of one amino acid and the amino group of the next, so it is what creates the polypeptide chain and therefore the primary structure. R groups project from that backbone and determine folding, but the bond itself does not hold them. Oxygen release is a function of haemoglobin's haem group rather than of any peptide bond.

94. The main role of mRNA during protein synthesis is to:

• A. Carry genetic information for protein synthesis
• B. Stabilize ribosome
• C. Deliver amino acids
• D. Provide platform for proteins synthesis

Explanation: Messenger RNA is transcribed from a gene and carries that base sequence out of the nucleus to the ribosome, where it is read in triplets. Delivering amino acids is the job of transfer RNA and providing the platform is the job of ribosomal RNA, so each of the three RNAs appears once among the options. Using a working copy protects the original DNA from the risks of the cytoplasm.

95. Glycoproteins are formed as a result of the combination of:

• A. Lipids and proteins
• B. Carbohydrates and proteins
• C. Nucleic acid and proteins
• D. Fatty acids and carbohydrates

Explanation: The prefix glyco means sugar, so a glycoprotein is protein joined to a carbohydrate group, and such molecules coat the cell surface where they act in recognition and as receptors. Lipid with protein gives a lipoprotein and nucleic acid with protein a nucleoprotein, both of which are conjugated molecules of other kinds. Reading the prefix identifies the non protein partner every time.