Biological Molecules

Biological Molecules MDCAT MCQs with answers

199 past paper MCQs from Biology unit 3, Biological Molecules, across 8 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Biological Molecules

1.Hydrolysis is the reverse of which process? (MDCAT 2022)

  1. condensation
  2. oxidation
  3. reduction
  4. hydrogenation
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Correct answer: (a) condensation

Condensation joins two molecules and removes water; hydrolysis adds water back and splits them.

2.Name the biomolecule essential for information storage and transmission within cells. (SIBA MDCAT 2025)

  1. Carbohydrates
  2. Lipids
  3. Nucleic acids.
  4. Proteins
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Correct answer: (c) Nucleic acids.

DNA holds the information and RNA carries it, so the nucleic acids are the information molecules.

3.Hydrolysis process is a reverse of -------------------- process. (UHS MDCAT 2023)

  1. Photolysis
  2. Condensation
  3. Deduction
  4. Convection
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Correct answer: (b) Condensation

Condensation joins two units with the loss of water; hydrolysis splits them by adding it back.

All 10 Biological Molecules MCQs → Biological Molecules notes →

Biological Importance of Water

4.Human bone cells contain what percentage of water? (MDCAT 2022)

  1. 20
  2. 40
  3. 85
  4. 90
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Correct answer: (a) 20

Bone is the driest tissue of the body, at about 20% water.

5.What is the percentage of water in bone cells? (MDCAT 2024)

  1. 70%
  2. 20%
  3. 98%
  4. 60%
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Correct answer: (b) 20%

Bone is the least watery of the tissues, with about a fifth of its weight as water.

6.Which property of water helps in moderating Earth's climate and maintaining stable temperature in aquatic environment? (UHS MDCAT 2025)

  1. Low viscosity
  2. High specific heat capacity
  3. High surface tension
  4. High polarity
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Correct answer: (b) High specific heat capacity

Water takes in a great deal of heat for a small rise in temperature, so it steadies the climate.

All 19 Biological Importance of Water MCQs → Biological Importance of Water notes →

Carbohydrates

7.Monosaccharides have a general formula represented by: (MDCAT 2024)

  1. $\mathrm{C_n(H_2O)_n}$
  2. $\mathrm{C(H_2O)_n}$
  3. $\mathrm{C_6(H_2O)_n}$
  4. $\mathrm{C_n(H_2O)}$
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Correct answer: (a) $\mathrm{C_n(H_2O)_n}$

A monosaccharide carries one water for every carbon, which is what "carbohydrate" means.

8.Polysaccharides in plants are synthesized by the process of: (MDCAT 2024)

  1. hydrolysis
  2. oxidation
  3. condensation
  4. glycolysis
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Correct answer: (c) condensation

Each glycosidic bond is made by removing a molecule of water between two sugars.

9.An oligosaccharide is made up of at least: (UHS MDCAT 2025)

  1. two saccharide units
  2. ten saccharide units
  3. three to ten saccharide units
  4. more than ten saccharide units
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Correct answer: (c) three to ten saccharide units

An oligosaccharide is three to ten monosaccharide units joined by glycosidic bonds.

All 46 Carbohydrates MCQs → Carbohydrates notes →

Proteins

10.The unique three-dimensional shape of a fully folded polypeptide constitutes its: (MDCAT 2022)

  1. primary structure
  2. secondary structure
  3. tertiary structure
  4. quaternary structure
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Correct answer: (c) tertiary structure

The whole folded shape of one chain is its tertiary structure.

11.Which of the following processes is involved in the breakdown of protein into amino acids? (MDCAT 2024)

  1. condensation
  2. hydrolysis
  3. glycolysis
  4. fixation
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Correct answer: (b) hydrolysis

A molecule of water is added across each peptide bond to break it.

12.Which of the following best highlights the importance of proteins in Immunity? (UHS MDCAT 2025)

  1. They act as receptors of pathogens
  2. They are long term energy reserves
  3. They act as antibodies
  4. They act as mechanical barrier to pathogens
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Correct answer: (c) They act as antibodies

Antibodies are proteins, and the specific defence of the body rests on them.

All 49 Proteins MCQs → Proteins notes →

Lipids

13.Butyric acid is a ______ carbon fatty acid. (MDCAT 2022)

  1. 4
  2. 6
  3. 12
  4. 3
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Correct answer: (a) 4

Butyric acid, the acid of rancid butter, has four carbons.

14.When glycerol reacts with a fatty acid, which type of chemical bond is formed? (MDCAT 2024)

  1. ester bond
  2. ether bond
  3. hydrogen bond
  4. ionic bond
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Correct answer: (a) ester bond

The acid and the alcohol condense to an ester, with water as the other product.

15.The hydrophilic end of a phospholipid molecule is polar because of the presence of: (MDCAT 2024)

  1. glycerol
  2. an amine group
  3. a fatty acid
  4. a phosphate group
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Correct answer: (d) a phosphate group

The charged phosphate head is what faces the water.

All 31 Lipids MCQs → Lipids notes →

Conjugated Molecules

16.Which of the following is a conjugated molecule? (MDCAT 2022)

  1. glycoproteins
  2. amino acids
  3. vitamins
  4. monosaccharides
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Correct answer: (a) glycoproteins

A conjugated molecule joins two classes of biomolecule, here a sugar with a protein.

17.Glycoproteins are formed as a result of the combination of: (UHS MDCAT 2025)

  1. Lipids and proteins
  2. Carbohydrates and proteins
  3. Nucleic acid and proteins
  4. Fatty acids and carbohydrates
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Correct answer: (b) Carbohydrates and proteins

A glycoprotein is a protein with a carbohydrate attached.

18.The glycoproteins are commonly found in: (KMU MDCAT 2025)

  1. Mitochondria
  2. Chloroplasts
  3. Ribosomes
  4. Plasma membrane
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Correct answer: (d) Plasma membrane

Glycoproteins stand on the outer face of the plasma membrane, where they act as markers and receptors.

19.Which of the following best describes glycoproteins? (SIBA MDCAT 2025)

  1. Proteins linked with carbohydrates
  2. Proteins linked with DNA
  3. Proteins linked with lipids
  4. Proteins linked with minerals
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Correct answer: (a) Proteins linked with carbohydrates

A glycoprotein is a protein carrying a carbohydrate chain.

Conjugated Molecules notes →

Ribonucleic Acid (RNA)

20.Which of the following is the correct higher (left) to lower (right) sequence of molecules with respect to the amount in the cell? (UHS MDCAT 2025)

  1. DNA → rRNA → tRNA → mRNA
  2. rRNA → tRNA → mRNA → DNA
  3. mRNA → tRNA → rRNA → DNA
  4. DNA → mRNA → tRNA → rRNA
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Correct answer: (b) rRNA → tRNA → mRNA → DNA

About four fifths of the RNA of a cell is ribosomal, then transfer, then messenger, and DNA is a different molecule altogether.

21.Which of the following is a key feature of RNA? (UHS MDCAT 2025)

  1. Deoxyribose and thymine
  2. Double stranded and thymine
  3. Ribose and uracil
  4. Ribose and thymine
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Correct answer: (c) Ribose and uracil

RNA carries ribose in place of deoxyribose and uracil in place of thymine.

22.Which of the following types of RNA makeup the largest proportion of total cellular RNA? (UHS MDCAT 2025)

  1. Messenger RNA
  2. Ribosomal RNA
  3. Transfer RNA
  4. Catalytic RNA (ribozyme)
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Correct answer: (b) Ribosomal RNA

Ribosomal RNA is the bulk of the cell’s RNA because ribosomes are so numerous.

All 17 Ribonucleic Acid (RNA) MCQs → Ribonucleic Acid (RNA) notes →

Structure of DNA

23.DNA stores biological information in discrete units termed: (MDCAT 2022)

  1. genes
  2. phenotypes
  3. karyotypes
  4. cells
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Correct answer: (a) genes

A gene is the length of nucleotides that codes for one polypeptide.

24.The complementary base pairing in DNA is important because it: (UHS MDCAT 2025)

  1. Maintains the tertiary structure of enzymes
  2. Provides energy for all cell metabolism
  3. Enables protein to fold properly
  4. Allows DNA act as a genetic blueprint during replication
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Correct answer: (d) Allows DNA act as a genetic blueprint during replication

Each strand specifies the other, so the base sequence can be copied faithfully and read as a blueprint.

25.In Watson and Crick's DNA model, which of the following pairs with Cytosine? (KMU MDCAT 2025)

  1. Adenine
  2. Guanine
  3. Thymine
  4. Uracil
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Correct answer: (b) Guanine

Cytosine pairs with guanine through three hydrogen bonds.

All 23 Structure of DNA MCQs → Structure of DNA notes →

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