Free Biological Molecules MCQs with Answers
1,790 Biological Molecules MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
The chapter covers water's polarity and biological roles, carbohydrates, lipids, proteins and nucleic acids, including their monomers, bonds, structures and functions. It also distinguishes RNA from DNA and explains conjugated molecules such as glycoproteins, glycolipids and nucleoproteins, which combine organic molecules with a non-protein component.
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- A. AUG
- B. UAA
- C. UUU
- D. GGC
Explanation: UAA, UAG, and UGA are stop codons (nonsense codons) that terminate translation.
Correct answer: UAA- A. Overlapping
- B. Non-overlapping and degenerate
- C. Ambiguous
- D. Different for each organism
Explanation: The genetic code is non-overlapping, degenerate (multiple codons for one amino acid), and universal.
Correct answer: Non-overlapping and degenerate- A. All bacteria
- B. Retroviruses
- C. All eukaryotes
- D. Plants only
Explanation: Reverse transcriptase synthesizes DNA from an RNA template, found in retroviruses like HIV.
Correct answer: Retroviruses- A. Maintains the tertiary structure of enzymes
- B. Provides energy for all cell metabolism
- C. Enables protein to fold properly
- D. Allows DNA act as a genetic blueprint during replication
Explanation: Because adenine always pairs with thymine and guanine with cytosine, each strand specifies the sequence of the other, so separating the…
Correct answer: Allows DNA act as a genetic blueprint during replication- A. Ionic bonds
- B. Hydrogen bonds
- C. Disulfide bridges
- D. Hydrophobic exclusion
Explanation: Regular hydrogen bonding between backbone carbonyl and amide groups coils the chain into an alpha helix or folds it into a beta pleated…
Correct answer: Hydrogen bonds- A. Keratin
- B. Collagen
- C. Hemoglobin
- D. Histone
Explanation: Haemoglobin folds into a compact soluble ball with hydrophilic residues outside, which is what lets it dissolve in the cytoplasm of a red…
Correct answer: Hemoglobin- A. Low viscosity
- B. High specific heat capacity
- C. High surface tension
- D. High polarity
Explanation: A great deal of energy goes into breaking hydrogen bonds before the temperature of water rises, so oceans and lakes absorb and release…
Correct answer: High specific heat capacity- A. two saccharide units
- B. ten saccharide units
- C. three to ten saccharide units
- D. more than ten saccharide units
Explanation: This is the option marked correct in the official UHS answer key, taking oligosaccharide in its broad sense of a few sugar units…
Correct answer: two saccharide units- A. DNA to rRNA to tRNA to mRNA
- B. rRNA to tRNA to mRNA to DNA
- C. mRNA to tRNA to rRNA to DNA
- D. DNA to mRNA to tRNA to rRNA
Explanation: This is the order given in the official UHS answer key. Among the three RNAs the ranking is not disputed: ribosomal RNA is by far the most…
Correct answer: DNA to rRNA to tRNA to mRNA- A. Deoxyribose and thymine
- B. Double stranded and thymine
- C. Ribose and uracil
- D. Ribose and thymine
Explanation: RNA carries ribose, which has a hydroxyl group at carbon 2, and uses uracil in place of thymine, and it is normally single stranded.
Correct answer: Ribose and uracil- 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…
Correct answer: Ribosomal RNA- 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.
Correct answer: Glycogen- 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…
Correct answer: Link amino acid- 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.
Correct answer: Carry genetic information for protein synthesis- 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…
Correct answer: Carbohydrates and proteins- A. Concentration of water molecules inside and outside the cell
- B. Concentration of enzymes on either side of the cell membrane
- C. Rate of molecular motion on either side of the cell membrane
- D. None of these
Explanation: Osmosis is the net movement of water across a selectively permeable membrane, driven by a difference in water concentration on the two…
Correct answer: Concentration of water molecules inside and outside the cell- A. 60%
- B. 65%
- C. 70%
- D. 75%
Explanation: Water commonly makes up about 70% of the body mass of a mammal, although the exact percentage varies with age, tissue type, and species.
Correct answer: 70%- A. Vitamin A
- B. Vitamin C
- C. Vitamin D
- D. B complex
Explanation: Vitamin A is converted into retinal, a component of rhodopsin, the light-sensitive pigment in rod cells of the retina.
Correct answer: Vitamin A- A. zero
- B. one
- C. negative
- D. two
Explanation: Water potential is defined relative to pure water, which is assigned a value of 0 MPa under standard reference conditions.
Correct answer: zero- A. imbibition
- B. plasmolysis
- C. deplasmolysis
- D. adhesion
Explanation: Plasmolysis occurs when a plant cell loses water by exosmosis, causing the protoplast to shrink away from the cell wall.
Correct answer: plasmolysis