Proteins Practice Questions
20 free Proteins practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following is the most abundant protein in the animal world?
- A Hemoglobin
- B Collagen
- C RuBisCO
- D Insulin
Correct answer: Collagen
Collagen is the most abundant protein in the animal world, providing structural support in connective tissues. In contrast, RuBisCO is the most abundant protein in the entire biosphere.
Proteins are considered to be _______ of amino acids.
- A Homopolymers (one type)
- B Heteropolymers (many types)
- C Non-polymers (no chain)
- D Dimers (two subunits)
Correct answer: Heteropolymers (many types)
Proteins are heteropolymers because they are made up of 20 different types of amino acids. A homopolymer would contain only one type of monomer repeated many times, whereas proteins require diverse amino acids for their diverse structure and function.
The chemical and physical properties of amino acids are essentially of the amino, carboxyl and the _______ functional groups.
- A Hydroxyl
- B Methyl
- C R-group
- D Nitrate
Correct answer: R-group
The R-group (side chain) determines the specific properties of each amino acid. Based on the nature of the R-group, amino acids can be acidic, basic, neutral, or aromatic.
In the 'Primary Structure' of a protein, the first amino acid is also called as:
- A C-terminal amino acid
- B N-terminal amino acid
- C R-terminal amino acid
- D Alpha-terminal amino acid
Correct answer: N-terminal amino acid
By convention, the first amino acid in a polypeptide chain is the N-terminal amino acid because its amino group is free. The last amino acid is the C-terminal amino acid.
Which type of protein structure is represented by a three-dimensional view that is absolutely necessary for many biological activities, such as enzymatic catalysis?
- A Primary
- B Secondary
- C Tertiary
- D Quaternary
Correct answer: Tertiary
Tertiary structure involves the folding of the polypeptide chain upon itself like a hollow woolen ball. This 3D shape creates active sites for enzymes to function.
Which of the following is an example of an aromatic amino acid?
- A Valine (aliphatic)
- B Tyrosine (aromatic)
- C Serine (hydroxyl)
- D Lysine (basic)
Correct answer: Tyrosine (aromatic)
Tyrosine, phenylalanine, and tryptophan are aromatic amino acids because they contain benzene ring side chains. Valine is a nonpolar aliphatic amino acid, Lysine is basic, and Serine is a hydroxyl-containing amino acid.
The protein that enables glucose transport into cells is:
- A Antibody (IgG)
- B Collagen (structural)
- C GLUT-4 (transporter)
- D Trypsin (protease)
Correct answer: GLUT-4 (transporter)
GLUT-4 (glucose transporter type 4) is a specific protein carrier that facilitates the movement of glucose across the cell membrane. It is crucial for maintaining blood sugar levels and is regulated by insulin.
In a protein, amino acids are linked by a peptide bond which is formed between the:
- A Between the carboxyl groups of two adjacent residues
- B Between the amino groups of two adjacent residues
- C Between the carboxyl and amino groups of adjacent residues
- D Between the R-groups of two adjacent amino acids
Correct answer: Between the carboxyl and amino groups of adjacent residues
A peptide bond is formed when the carboxyl (-COOH) group of one amino acid reacts with the amino (-NH2) group of the next amino acid, releasing water in a condensation reaction.
Adult human hemoglobin consists of how many subunits?
- A Two subunits (1 alpha, 1 beta)
- B Four subunits (2 alpha, 2 beta)
- C Three subunits (2 alpha, 1 beta)
- D Four subunits (4 alpha)
Correct answer: Four subunits (2 alpha, 2 beta)
Human hemoglobin is a quaternary structure made of four polypeptide chains. Specifically, it consists of two alpha-type subunits and two beta-type subunits.
The secondary structure of protein, such as the alpha-helix, is stabilized primarily by:
- A Peptide bonds
- B Hydrogen bonds
- C Ionic bonds
- D Disulfide bonds
Correct answer: Hydrogen bonds
Hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the polypeptide backbone stabilize secondary structures like the alpha-helix and beta-pleated sheets. Disulfide bonds contribute to tertiary structure.
Essential amino acids are those which:
- A Our body can synthesize them
- B Not needed for protein synthesis
- C Must be provided through diet
- D Contain only sulfur atoms
Correct answer: Must be provided through diet
Essential amino acids cannot be manufactured by the body in sufficient quantities and must be obtained from food. There are 9 essential amino acids in humans. Non-essential amino acids are those the body can synthesize on its own.
A particular property of amino acids is the ionizable nature of -NH2 and -COOH groups. In solutions of different pHs, the structure of amino acids changes. The form with both positive and negative charges is called:
- A Anion (negative charge)
- B Cation (positive charge)
- C Zwitterion (dual charge)
- D Non-polar (no charge)
Correct answer: Zwitterion (dual charge)
The zwitterionic form occurs when the amino acid carries both a positive charge (on -NH3⁺) and a negative charge (on -COO⁻), resulting in a net neutral charge. This form predominates near the amino acid's isoelectric point.
Which of the following functions is NOT typically performed by proteins?
- A Acting as hormones (e.g., insulin)
- B Acting as receptors (e.g., sensory reception)
- C Primary storage of genetic information
- D Fighting infectious agents as antibodies
Correct answer: Primary storage of genetic information
Genetic information is primarily stored in nucleic acids (DNA and RNA), not proteins. Proteins perform diverse roles like catalysis, transport, and structural support.
If a protein consists of more than one polypeptide chain, the arrangement of these subunits with respect to each other is known as:
- A Primary structure of the chain
- B Secondary structure of the chain
- C Tertiary structure of the chain
- D Quaternary structure
Correct answer: Quaternary structure
Quaternary structure describes the spatial arrangement and interaction of multiple polypeptide subunits. Hemoglobin is a classic example of this level of organization.
Which of the following is an acidic amino acid?
- A Lysine (basic)
- B Arginine (basic)
- C Glutamic acid
- D Alanine (neutral)
Correct answer: Glutamic acid
Glutamic acid and aspartic acid have an extra carboxyl group in their R-group, making them acidic. Lysine and arginine are basic amino acids.
In the alpha-helix secondary structure, the polypeptide chain is coiled in which direction?
- A Left-handed
- B Right-handed
- C Both directions
- D Randomly
Correct answer: Right-handed
In proteins, only right-handed helices are observed. This specific coiling is a hallmark of the alpha-helix secondary structure.
The simplest amino acid, where the R-group is represented by a hydrogen atom, is:
- A Alanine
- B Serine
- C Glycine
- D Leucine
Correct answer: Glycine
In Glycine, the R-group is a simple hydrogen atom. In Alanine it is a methyl group, and in Serine it is a hydroxy-methyl group.
Which of the following proteins acts as an intercellular ground substance?
- A Trypsin
- B Collagen
- C Insulin
- D Hemoglobin
Correct answer: Collagen
Collagen provides the structural framework and serves as the primary intercellular ground substance in various connective tissues.
A protein's primary structure provides information about:
- A The three-dimensional folding pattern
- B The linear sequence of amino acids
- C The location of disulfide bridges only
- D The enzymatic activity of the protein
Correct answer: The linear sequence of amino acids
The primary structure is the linear sequence of amino acids. It tells us which amino acid is at the first position, second position, and so on.
Which of the following is a basic amino acid?
- A Valine
- B Glutamate
- C Lysine
- D Tyrosine
Correct answer: Lysine
Lysine is a basic amino acid because its R-group contains an additional amino group. Valine is neutral, glutamate is acidic, and tyrosine is aromatic.