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. the sugars bond only to purines
- B. phosphate groups pair with pyrimidines
- C. hydrogen bonds form only between bases of equal size
- D. each base pair contains one purine and one pyrimidine
Explanation: Adenine and guanine are the purines, thymine and cytosine the pyrimidines, and every pair across the helix matches one of each.
Correct answer: each base pair contains one purine and one pyrimidine- A. alternating bases and phosphate groups
- B. bases only, stacked one above another
- C. alternating deoxyribose sugars and phosphate groups
- D. alternating sugars and bases
Explanation: Phosphodiester bonds link the sugar of one nucleotide to the phosphate of the next, making a repeating sugar phosphate rail with the bases…
Correct answer: alternating deoxyribose sugars and phosphate groups- A. contains one old strand and one newly synthesised strand
- B. is built entirely from new nucleotides
- C. conserves only half of its original bases
- D. is rebuilt only in every second cell cycle
Explanation: When the two parental strands separate, each serves as a template for a new partner, so both daughter helices retain one original strand.
Correct answer: contains one old strand and one newly synthesised strand- A. adenine equals guanine and cytosine equals thymine
- B. the amount of adenine is always greater than that of thymine
- C. the amount of adenine equals thymine and guanine equals cytosine
- D. purines are always more numerous than pyrimidines
Explanation: Because A pairs with T and G pairs with C across the helix, their amounts must match in any double stranded DNA.
Correct answer: the amount of adenine equals thymine and guanine equals cytosine- A. Glycosidic bond
- B. Peptide bond
- C. Ester bond
- D. Phosphodiester bond
Explanation: A peptide bond (amide bond) forms between the carboxyl group of one amino acid and the amino group of another, with loss of water.
Correct answer: Peptide bond- A. Benedict's test
- B. Iodine test
- C. Biuret test
- D. Emulsion test
Explanation: Biuret test uses NaOH and CuSO4 to detect peptide bonds, giving a purple/violet color with proteins.
Correct answer: Biuret test- A. α-helix and β-pleated sheet
- B. Quaternary folding
- C. Amino acid sequence
- D. Disulfide bridges
Explanation: Secondary structure involves local folding into α-helix or β-pleated sheet, stabilized by hydrogen bonds between backbone atoms.
Correct answer: α-helix and β-pleated sheet- A. Triglyceride
- B. Phospholipid
- C. Steroid
- D. Wax
Explanation: Phospholipids form the lipid bilayer of cell membranes due to their amphipathic nature (hydrophilic head, hydrophobic tails).
Correct answer: Phospholipid- A. β-glucose
- B. α-glucose
- C. Fructose
- D. Galactose
Explanation: Both starch and glycogen are polymers of α-glucose, linked by α-1,4 and α-1,6 glycosidic bonds.
Correct answer: α-glucose- A. Vitamin C
- B. Vitamin B12
- C. Vitamin D
- D. Vitamin B6
Explanation: Vitamins A, D, E, and K are fat-soluble. Vitamin C and B vitamins are water-soluble.
Correct answer: Vitamin D- A. Pepsin
- B. Trypsin
- C. Salivary amylase
- D. Lipase
Explanation: Salivary amylase (ptyalin) begins starch digestion in the mouth, breaking it into maltose.
Correct answer: Salivary amylase- 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.
Correct answer: Lipid- 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).
Correct answer: Being nucleic acids- 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.
Correct answer: Watson and Crick- 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.
Correct answer: Semi-conservative- A. DNA polymerase
- B. Helicase
- C. Ligase
- D. Primase
Explanation: Helicase breaks hydrogen bonds between base pairs, unwinding the DNA double helix.
Correct answer: Helicase- 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'.
Correct answer: Lagging strand- 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.
Correct answer: An RNA copy of DNA- A. UAA
- B. AUG
- C. UAG
- D. UGA
Explanation: AUG codes for methionine and serves as the start codon, initiating protein synthesis.
Correct answer: AUG80. 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.
Correct answer: Non-coding sequences removed during splicing