Proteins

Proteins MDCAT MCQs with answers

49 past paper MCQs on Proteins, from the Biological Molecules unit of MDCAT Biology. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.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.

2.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.

3.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.

4.The secondary structure of proteins is stabilized by: (UHS MDCAT 2025)

  1. Ionic bonds
  2. Hydrogen bonds
  3. Disulfide bridges
  4. Hydrophobic exclusion
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Correct answer: (b) Hydrogen bonds

Hydrogen bonds between the peptide groups hold the alpha helix and the beta pleated sheet.

5.The following is an example of a globular protein. (UHS MDCAT 2025)

  1. Keratin
  2. Collagen
  3. Hemoglobin
  4. Histone
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Correct answer: (c) Hemoglobin

Haemoglobin is globular and soluble; keratin and collagen are fibrous.

6.Peptide bonds are Important In protein because they: (UHS MDCAT 2025)

  1. Affect solubility
  2. Hold R-groups
  3. Link amino acid
  4. help in releasing oxygen
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Correct answer: (c) Link amino acid

The peptide bond joins the amino group of one amino acid to the carboxyl group of the next.

7.Which of the following is NOT a globular protein? (KMU MDCAT 2025)

  1. Enzyme
  2. Albumin
  3. Hemoglobin
  4. Collagen
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Correct answer: (d) Collagen

Collagen is a fibrous structural protein; the other three are globular.

8.An experiment shows that heating a 'protein' disrupts the alpha helix structure. Which protein structure is mainly affected? (KMU MDCAT 2025)

  1. Primary structure
  2. Secondary structure
  3. Tertiary structure
  4. Quaternary structure
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Correct answer: (b) Secondary structure

The alpha helix is secondary structure, held by hydrogen bonds that heat breaks first.

9.A food sample contains long chains of amino acids bounded together. This indicates the presence of: (SIBA MDCAT 2025)

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

A long chain of amino acids is a polypeptide, so the sample is protein.

10.Name the type of bond that join amino acids to form a polypeptide chain: (SIBA MDCAT 2025)

  1. Hydrogen bond
  2. Ionic bond
  3. Glycosidic bond
  4. Peptide bond
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Correct answer: (d) Peptide bond

Amino acids are joined by peptide bonds between the amino group of one and the carboxyl group of the next.

11.A mutation prevents proper disulphide bond formation in a fibrous protein, causing brittle nails and slow hair growth. Which of the following proteinaceous substance would be affected? (SZABMU MDCAT 2025)

  1. Elastin
  2. Actin
  3. Keratin
  4. Collagen
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Correct answer: (c) Keratin

Keratin of hair and nail owes its toughness to disulphide bridges between cysteine residues.

12.Which of the following process Is involved in breakdown of protein into Amino acids? (UHS MDCAT 2024)

  1. Condensation
  2. Hydrolysis
  3. Glycolysis
  4. Fixation
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Correct answer: (b) Hydrolysis

Hydrolysis adds water across each peptide bond and frees the amino acids.

13.Sickle cell anaemia results from? (KMU MDCAT 2024)

  1. Reduction in oxygen carrying capacity of haemoglobin
  2. Linkage between the polypeptide chains
  3. Single amino acid substitution in the haemoglobin molecule
  4. Viral infections of RNA viruses
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Correct answer: (c) Single amino acid substitution in the haemoglobin molecule

A single valine in place of glutamic acid in the beta chain is the whole of the change.

14.Which is INCORRECT about the globular proteins? (KMU MDCAT 2024)

  1. Abundantly found in hair
  2. Are spherical in shape
  3. Have polypeptide chains
  4. Soluble in water
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Correct answer: (a) Abundantly found in hair

Hair is keratin, a fibrous protein; globular proteins are the soluble, rounded ones.

15.Protein present in haemoglobin has _______ structure. (KMU MDCAT 2024)

  1. Primary
  2. Secondary
  3. Tertiary
  4. Quaternary
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Correct answer: (d) Quaternary

Haemoglobin has four polypeptide chains fitted together, which is quaternary structure.

16.Proteins with tertiary structure are helpful in: (NUMS MDCAT 2024)

  1. Carrying messages from glands to target organs
  2. Maintaining epithelial lining of skin
  3. Making the matrix of connective tissue
  4. Helping muscle contraction
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Correct answer: (a) Carrying messages from glands to target organs

Peptide hormones are globular proteins folded into a tertiary shape that their receptors recognize.

17.Rebounding is process of straightening the curly hairs. Which bond is targeted by oxidizing agents used during this process? (NUMS MDCAT 2024)

  1. Peptide bond
  2. Ionic bond
  3. Disulphide bridge
  4. Hydrogen bond
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Correct answer: (c) Disulphide bridge

The curl of hair is held by disulphide bridges, and the oxidizing agent breaks and remakes them.

18.Ions of heavy metal are harmful for living organisms because of their ability to: (NUMS MDCAT 2024)

  1. Cleave nucleic acid
  2. Interfere with fat metabolism
  3. Break glycosidic bonds
  4. Destabilize proteins
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Correct answer: (d) Destabilize proteins

Heavy metal ions bind the sulphydryl groups and unfold the protein.

19.Unique three-dimensional shape of the fully folded polypeptide, constitutes: (UHS MDCAT 2023)

  1. Primary structure of protein
  2. Secondary structure of protein
  3. Tertiary structure of protein
  4. Quaternary structure of protein
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Correct answer: (c) Tertiary structure of protein

The folded shape of a whole polypeptide is its tertiary structure.

20.Proteins are the main ---------- of the cell? (UHS MDCAT 2023)

  1. Physiological components
  2. Functional components
  3. Structural components
  4. Biological components
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Correct answer: (b) Functional components

Enzymes, carriers, receptors and antibodies are all proteins, so proteins do the work of the cell.

21.Which of the following proteins acts as carrier of copper in blood plasma? (UHS MDCAT 2023)

  1. Hemoglobin
  2. Glycoprotein
  3. Ceruloplasmin
  4. Histone
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Correct answer: (c) Ceruloplasmin

Ceruloplasmin is the copper carrying protein of the plasma.

22.Select an example of fibrous protein: (SZABMU MDCAT 2023)

  1. Enzymes
  2. Collagen
  3. Hemoglobin
  4. Hormones
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Correct answer: (b) Collagen

Collagen is a fibrous structural protein of tendon, skin and bone.

23.Which function is NOT performed by proteins? (SZABMU MDCAT 2023)

  1. Providing structural support to cell
  2. Catalyzing biochemical reactions
  3. Transporting materials across cell membrane
  4. Providing insulation against heat loss
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Correct answer: (d) Providing insulation against heat loss

Insulation against heat loss is the work of fat, not of protein.

24.Based on function, thyroxin can be classified as: (SZABMU MDCAT 2023)

  1. Hormonal protein
  2. Structural protein
  3. Transprt protein
  4. Genetic protein
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Correct answer: (a) Hormonal protein

Thyroxine carries a message from a gland to its target, so it is classed as a hormonal protein.

25.Which of the following protein establishes the matrix of bone and cartilage? (NUMS MDCAT 2023)

  1. Elastin
  2. Keratin
  3. Collagen
  4. Histone
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Correct answer: (c) Collagen

Collagen fibres are the framework of the matrix of both bone and cartilage.

26.Insulin consists of two polypeptides containing 21 amino acids and 30 amino acids each. How many peptide bonds does the insuline contain? (PMC MDCAT 2022)

  1. 51
  2. 50
  3. 49
  4. 2
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Correct answer: (c) 49

Each chain of $n$ residues has $n-1$ bonds, so $20+29$ is $49$.

27.If an α-helix of a polypeptide consist of 360 amino acids, how many turns does the helix contain? (PMC MDCAT 2022)

  1. 3.6 turns
  2. 100 turns
  3. 360 turns
  4. The number of turns can not be determind
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Correct answer: (b) 100 turns

An alpha helix turns once every $3.6$ residues, so $360$ residues make $100$ turns.

28.The R-group in glycine consists of: (PMC MDCAT 2022)

  1. A Hydrogen atom
  2. Methyl group
  3. Amino group
  4. Carboxylic acid group
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Correct answer: (a) A Hydrogen atom

Glycine is the simplest amino acid; its side chain is a single hydrogen atom.

29.The globular structure of enzymes shows: (PMC MDCAT 2022)

  1. Primary structure of protein
  2. Secondary structure of protein
  3. Tertiary structure of protein
  4. That it's an organic catalysis
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Correct answer: (c) Tertiary structure of protein

A globular, folded shape is tertiary structure.

30.Which of the following is an example of a globular protein? (PMC MDCAT 2022)

  1. Keratin
  2. An enzyme
  3. Fibrinogen
  4. Collagen
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Correct answer: (b) An enzyme

Enzymes are globular and soluble; keratin, fibrinogen and collagen are fibrous.

31.The R group of an amino acid represents: (PMC MDCAT 2022)

  1. a hydrogen atom
  2. A hydrocarbon
  3. an additional atom or group of atoms
  4. a methyl group
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Correct answer: (c) an additional atom or group of atoms

The R group is whatever side chain is attached to the alpha carbon.

32.The osmotic pressure of blood Is maintained by: (PMC MDCAT 2022)

  1. Membrane proteins
  2. Fibrous proteins
  3. Plasma proteins
  4. Myosln
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Correct answer: (c) Plasma proteins

The plasma proteins, chiefly albumin, hold the osmotic pressure of the blood.

33.The tertiary structure of protein indicates its: (PMC MDCAT 2022)

  1. Chemical function
  2. Biological function
  3. Physical appereance
  4. characterstics
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Correct answer: (b) Biological function

A protein works only when folded into its tertiary shape.

34.When two amino acids such as glycine and alanine are variously arranged to make dipeptides. How many different dipeptide combinations can be produced? (PMC MDCAT 2022)

  1. 1
  2. 2
  3. 3
  4. 4
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Correct answer: (d) 4

Each of the two can come first and each can come second, so there are four arrangements.

35.Hydrogen bonding produces a regular coiled arrangement in proteins called: (PMC MDCAT 2022)

  1. α-hellx
  2. β-hellx
  3. Tertiary conformation
  4. Quaternary structure
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Correct answer: (a) α-hellx

Hydrogen bonds between the peptide groups hold the alpha helix.

36.Which of the following Is correct about globular proteins? (PMC MDCAT 2022)

  1. Insoluble In water
  2. Elastic in nature
  3. Can be crystalized
  4. their final structure is secondary
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Correct answer: (c) Can be crystalized

Globular proteins are soluble and can be crystallized; the fibrous ones cannot.

37.Plasma proteins are synthesized In: (PMC MDCAT 2022)

  1. Gall bladder
  2. Liver
  3. Spleen
  4. Skin
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Correct answer: (b) Liver

Albumin, globulins and fibrinogen are all made in the liver.

38.Which of the following bonds maintain the primary structure of a protein (PMC MDCAT 2022)

  1. Hydrogen bonds
  2. Peptide bonds
  3. Disulphide bonds
  4. Hydrophobic Interaction
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Correct answer: (b) Peptide bonds

The primary structure is the order of the amino acids, held by peptide bonds.

39.Which of the following molecule contains amino acid?: (NUMS MDCAT 2022)

  1. Cellulose
  2. Collagen
  3. Sucrose
  4. Ascorbic acid
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Correct answer: (b) Collagen

Collagen is a protein, and proteins are chains of amino acids.

40.Which type of bond is not responsible in maintaining the tertiary structure of proteins? (PMC Practice 2021)

  1. Ionic
  2. Hydrogen
  3. Peptide
  4. Glycosidic
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Correct answer: (d) Glycosidic

A glycosidic bond joins sugars; protein folding is held by hydrogen, ionic and disulphide bonds.

41.The structure of a fibrous protein comprises of polypeptide chains in the form of: (UHS MDCAT 2019)

  1. Cluster
  2. Spherical or curried up ball
  3. Long strands or fibrils
  4. Flat uncoiled chains
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Correct answer: (c) Long strands or fibrils

A fibrous protein is drawn out into long strands, which is what makes it strong and insoluble.

42.In glycine, R is __________. (UHS MDCAT 2019)

  1. Ethane
  2. Fatty acid
  3. H atom
  4. Competitive reversible
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Correct answer: (c) H atom

Glycine is the simplest amino acid; its side chain is a single hydrogen atom.

43.Most proteins are made up of: (UHS MDCAT 2019)

  1. 10 types of Amino acids
  2. 20 types of Amino acids
  3. 170 types Of Amino acids
  4. 16 types of Amino acids
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Correct answer: (b) 20 types of Amino acids

Twenty amino acids are coded for and make up almost all proteins.

44.The number and sequence of amino acids along a polypeptide chain is called _______ structure of a protein. (UHS MDCAT 2018)

  1. Quaternary
  2. Tertiary
  3. Primary
  4. Secondary
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Correct answer: (c) Primary

The order of the amino acids is the primary structure.

45.Which of the following holds the alpha helix of protein in its place: (UHS MDCAT 2018)

  1. R group
  2. Disulfide bond
  3. Amino group
  4. Hydrogen bond
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Correct answer: (d) Hydrogen bond

Hydrogen bonds between the peptide groups hold the coil of the alpha helix.

46.How many essential amino acids are there? (UHS MDCAT 2017)

  1. Three
  2. Six
  3. Nine
  4. Twelve
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Correct answer: (c) Nine

Nine of the twenty amino acids cannot be made by the body and must come in the diet.

47.The type of bonding in ?-Helix; (UHS MDCAT 2017)

  1. 1,2 Glycosidic Linkage
  2. Ionic Bond
  3. Disulfide Bond
  4. Hydrogen Bond
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Correct answer: (d) Hydrogen Bond

Hydrogen bonds between the peptide groups hold the coil of the alpha helix.

48.The sequence of amino acids is major factor in which type of protein classification; (UHS MDCAT 2017)

  1. Primary Proteins
  2. Secondary Proteins
  3. Tertiary Proteins
  4. Both Primary and Tertiary Proteins
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Correct answer: (a) Primary Proteins

The order of the amino acids is the primary structure.

49.Secondary structure of protein is found in: (UHS MDCAT 2016)

  1. Trypsin
  2. Keratin
  3. Insulin
  4. Glucagon
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Correct answer: (b) Keratin

Keratin is a fibrous protein whose chains are held in the alpha helix, its secondary structure.

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