Proteins & Amino Acids — NEET Biology MCQs with Solutions
Free NEET Biology Proteins & Amino Acids MCQs with step-by-step solutions (65 questions). Part of Biomolecules. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Proteins & Amino Acids · easy · theory
The number of amino acids that commonly occur in proteins is:
A. 4
B. 10
C. 64
D. 20 ✓ Correct
Solution: Twenty standard amino acids make up proteins; each has an amino group, carboxyl group, H and an R group on the α-carbon.
Q2 — Proteins & Amino Acids · easy · theory
The bond that links two amino acids in a protein is the:
A. Hydrogen bond
B. Phosphodiester bond
C. Peptide bond ✓ Correct
D. Glycosidic bond
Solution: A peptide (amide) bond forms between the –COOH of one amino acid and the –NH₂ of the next, with loss of water.
Q3 — Proteins & Amino Acids · medium · theory
The nature of an amino acid (acidic, basic or neutral) is decided by its:
A. Amino group
B. Carboxyl group
C. R group (side chain) ✓ Correct
D. Alpha carbon
Solution: The R group determines the chemical/functional character of the amino acid (e.g. glutamic acid = acidic, lysine = basic).
Q4 — Proteins & Amino Acids · medium · theory
Amino acids that cannot be synthesised by the human body and must be taken in the diet are called:
A. Essential amino acids ✓ Correct
B. Semi-essential amino acids
C. Non-essential amino acids
D. Secondary metabolites
Solution: Essential amino acids must be obtained from food; the body can synthesise non-essential ones.
Q5 — Proteins & Amino Acids · hard · theory
A zwitterion form of an amino acid exists at physiological pH because:
A. Both groups are neutral
B. The R group is always charged
C. It has no charge at any pH
D. The amino group is protonated (+) and the carboxyl group is ionised (−) simultaneously ✓ Correct
Solution: At neutral pH amino acids bear both a positive (–NH₃⁺) and a negative (–COO⁻) charge — the zwitterion (dipolar) form.
Q6 — Proteins & Amino Acids · hard · theory
The average molecular mass of an amino acid residue in a protein (~110 Da) is less than the free amino acid because:
A. Amino acids gain mass on polymerising
B. The R group is removed
C. A molecule of water is lost during each peptide bond formation ✓ Correct
D. Proteins contain no water
Solution: Peptide bond formation is a condensation (dehydration), so each residue is lighter than the free amino acid by ~18 Da.
Q7 — Proteins & Amino Acids · easy · numerical
In an amino acid, the amino group, carboxyl group, a hydrogen and the R-group are all attached to the:
A. same α-carbon atom ✓ Correct
B. nitrogen atom of the amino group
C. carbon of the carboxyl group
D. β-carbon atom
Solution: Amino acids are substituted methanes in which all four groups (–NH₂, –COOH, –H and –R) are attached to the same central α-carbon.
Q8 — Proteins & Amino Acids · easy · numerical
Which amino acid contains sulphur in its side chain (R-group)?
A. Alanine
B. Glycine
C. Serine
D. Cysteine ✓ Correct
Solution: Cysteine (and methionine) carry sulphur in their R-groups; glycine, alanine and serine do not.
Q9 — Proteins & Amino Acids · easy · numerical
The simplest amino acid, whose R-group is just a hydrogen atom, is:
A. Valine
B. Glycine ✓ Correct
C. Alanine
D. Serine
Solution: Glycine has hydrogen as its R-group, making it the smallest and simplest amino acid.
Q10 — Proteins & Amino Acids · easy · numerical
Which one of the following is an essential amino acid for humans?
A. Alanine
B. Lysine ✓ Correct
C. Glycine
D. Serine
Solution: Lysine cannot be synthesised by the human body and must be obtained from the diet; glycine, alanine and serine are non-essential.
Q11 — Proteins & Amino Acids · medium · numerical
At a pH well below its isoelectric point, an amino acid predominantly exists as:
A. an uncharged molecule with no ionised groups
B. a permanently double-negative ion
C. a positively charged cation (–NH₃⁺ and –COOH) ✓ Correct
D. a negatively charged anion (–NH₂ and –COO⁻)
Solution: In strongly acidic conditions the carboxyl group stays protonated (–COOH) while the amino group is –NH₃⁺, giving the amino acid a net positive (cationic) charge.
Q12 — Proteins & Amino Acids · medium · numerical
Aspartic acid and glutamic acid are classified as acidic amino acids because their R-groups:
A. are non-polar hydrocarbon chains
B. contain an additional carboxyl (–COOH) group ✓ Correct
C. contain an additional amino (–NH₂) group
D. contain a sulphur atom
Solution: The extra –COOH in their side chains makes aspartic and glutamic acids acidic; basic amino acids (e.g. lysine) instead carry an extra amino group.
Q13 — Proteins & Amino Acids · medium · numerical
A peptide bond is formed between the ______ of one amino acid and the ______ of the next, with the loss of a water molecule:
A. carboxyl group; amino group ✓ Correct
B. R-group; carboxyl group
C. carboxyl group; R-group
D. amino group; amino group
Solution: The peptide (amide) bond forms by dehydration between the –COOH of one amino acid and the –NH₂ of the next.
Q14 — Proteins & Amino Acids · medium · numerical
Which one of the following correctly pairs an amino acid with the nature of its R-group?
A. Glycine – basic
B. Lysine – basic ✓ Correct
C. Glutamic acid – neutral
D. Valine – acidic
Solution: Lysine has an extra amino group and is basic; glutamic acid is acidic, valine is non-polar/neutral and glycine is neutral.
Q15 — Proteins & Amino Acids · medium · numerical
Assertion (A): About twenty amino acids commonly occur in proteins. Reason (R): Each amino acid differs from another only in the nature of its R-group.
A. A is true but R is false
B. Both A and R are true and R is the correct explanation of A
C. Both A and R are true but R is not the correct explanation of A ✓ Correct
D. A is false but R is true
Solution: Both statements are true, but the fact that there are 20 amino acids is not explained by their differing R-groups; the R-group merely distinguishes one from another.
Q16 — Proteins & Amino Acids · medium · numerical
The amino acids found in proteins are called α-amino acids because:
A. the amino group is attached to the carbon next to the carboxyl group (the α-carbon) ✓ Correct
B. they contain an alpha-helix in every molecule
C. they always carry an acidic R-group
D. they were the first biomolecules ever discovered
Solution: The prefix α refers to the position of the amino group on the carbon adjacent to the –COOH, i.e. the α-carbon.
Q17 — Proteins & Amino Acids · easy
Peptide bond is formed when the
A. Carboxyl group of one amino acid reacts with amino group of the next amino acid ✓ Correct
B. Carboxyl group of one amino acid reacts with the carboxyl group of the next amino acid
C. Amino group of one amino acid reacts with carboxyl group of the next amino acid
D. Amino group of one amino acid reacts with the amino group of the next amino acid
Solution: A peptide bond forms when the carboxyl (-COOH) group of one amino acid reacts with the amino (-NH2) group of the next amino acid.
Q18 — Proteins & Amino Acids · easy
Assertion: Amino acids are called alpha-amino acids. Reason: Amino acids are organic compounds containing an amino group and a carboxyl group as substituents on the same carbon.
A. Both assertion and reason are true, but reason is not the correct explanation of the assertion.
B. Both assertion and reason are true and the reason is the correct explanation of the assertion. ✓ Correct
C. Both assertion and reason are false.
D. Assertion is true, but reason is false.
Solution: Amino acids are termed alpha-amino acids precisely because the amino and carboxyl groups are attached to the same (alpha) carbon.
Q19 — Proteins & Amino Acids · medium
Assertion: Human diet should compulsorily contain glycine, serine and tyrosine. Reason: Essential amino acids cannot be synthesized in the human body.
A. Both assertion and reason are true and the reason is the correct explanation of the assertion.
B. Both assertion and reason are false. ✓ Correct
C. Both assertion and reason are true, but reason is not the correct explanation of the assertion.
D. Assertion is true, but reason is false.
Solution: Glycine, serine and tyrosine are non-essential amino acids that the body can synthesize, so the assertion is false even though the reason's general statement is true it does not save the pairing.
Q20 — Proteins & Amino Acids · easy
Assertion: The amino acid glycine comes under the category of non-essential amino acids. Reason: This is due to the fact that it cannot be synthesised in the body.
A. Assertion is true, but reason is false. ✓ Correct
B. Both assertion and reason are true, but reason is not the correct explanation of the assertion.
C. Both assertion and reason are false.
D. Both assertion and reason are true and the reason is the correct explanation of the assertion.
Solution: Glycine is non-essential because it CAN be synthesized in the body, so the reason is false.
Q21 — Proteins & Amino Acids · medium
Match Column I with Column II. Column I: a. Acidic amino acid, b. Basic amino acid, c. Neutral amino acid, d. Aromatic amino acid. Column II: 1. Lysine, 2. Valine, 3. Tyrosine, 4. Glutamic acid.
A. a-4, b-2, c-1, d-3
B. a-1, b-2, c-3, d-4
C. a-4, b-1, c-2, d-3 ✓ Correct
D. a-1, b-3, c-4, d-2
Solution: Glutamic acid is acidic (4), lysine is basic (1), valine is neutral (2), tyrosine is aromatic (3). Hence a-4, b-1, c-2, d-3.
Q22 — Proteins & Amino Acids · medium
Match Column I with Column II. Column I: a. Enzyme, b. Hormone, c. Fight infectious agents, d. Intercellular ground substance. Column II: 1. Collagen, 2. Trypsin, 3. Insulin, 4. Antibody.
A. a-3, b-2, c-4, d-1
B. a-2, b-3, c-1, d-4
C. a-2, b-4, c-1, d-3
D. a-2, b-3, c-4, d-1 ✓ Correct
Solution: Enzyme = trypsin (2), hormone = insulin (3), fights infectious agents = antibody (4), intercellular ground substance = collagen (1). Hence a-2, b-3, c-4, d-1.
Q23 — Proteins & Amino Acids · medium
Match Column I with Column II. Column I: a. Acidic amino acid, b. Basic amino acid, c. Neutral amino acid, d. Aromatic amino acid. Column II: 1. Valine, 2. Glutamic acid, 3. Phenylalanine, 4. Lysine.
A. a-2, b-4, c-1, d-3 ✓ Correct
B. a-2, b-1, c-4, d-3
C. a-3, b-2, c-1, d-4
D. a-1, b-4, c-3, d-2
Solution: Glutamic acid is acidic (2), lysine is basic (4), valine is neutral (1), phenylalanine is aromatic (3). Hence a-2, b-4, c-1, d-3.
Q24 — Proteins & Amino Acids · medium
Given below are two statements:
Statement I: Amino acids have a property of ionizable nature of -NH2 and -COOH groups, hence have different structures at different pH.
Statement II: Amino acids can exist as Zwitterionic form at acidic and basic pH.
In the light of the above statements, choose the most appropriate answer.
A. Both Statement I and Statement II are incorrect
B. Statement I is correct but Statement II is incorrect ✓ Correct
C. Statement I is incorrect but Statement II is correct
D. Both Statement I and Statement II are correct
Solution: The ionizable -NH2 and -COOH groups make amino acid structure depend on pH (Statement I true). The zwitterionic form exists at the isoelectric (neutral) pH, not at acidic and basic pH (Statement II false).
Q25 — Proteins & Amino Acids · medium
Match List-I with List-II.
List-I: A. GLUT-4, B. Insulin, C. Trypsin, D. Collagen.
List-II: I. Hormone, II. Enzyme, III. Intercellular ground substance, IV. Enables glucose transport into cells.
A. A-II, B-III, C-IV, D-I
B. A-III, B-IV, C-I, D-II
C. A-I, B-II, C-III, D-IV
D. A-IV, B-I, C-II, D-III ✓ Correct
Solution: GLUT-4 enables glucose transport into cells (IV); insulin is a hormone (I); trypsin is an enzyme (II); collagen forms the intercellular ground substance (III).
Q26 — Proteins & Amino Acids · medium
Which one of the following is the most abundant protein in the animals?
A. Lectin
B. Collagen ✓ Correct
C. Insulin
D. Haemoglobin
Solution: Collagen is the most abundant protein in the animal world, forming the main structural protein of connective tissue.
Q27 — Proteins & Amino Acids · medium
Which of the following glucose transporters is insulin-dependent?
A. GLUT III
B. GLUT II
C. GLUT I
D. GLUT IV ✓ Correct
Solution: GLUT IV is the insulin-dependent glucose transporter present in muscle and adipose tissue.
Q28 — Proteins & Amino Acids · medium
Amino acids, as the name suggests, have both an amino group and a carboxyl group in their structure. In addition, all naturally occurring amino acids (those which are found in proteins) are called L-amino acids. From this, can you guess from which compound can the simplest amino acid be made?
A. Phenol
B. Glycine
C. Methane ✓ Correct
D. Formic acid
Solution: Amino acids are substituted methanes: the central carbon (as in methane) carries an amino group, a carboxyl group, a hydrogen and an R-group. The simplest amino acid, glycine, is derived from methane.
Q29 — Proteins & Amino Acids · easy
Many organic substances are negatively charged, for e.g., acetic acid, while others are positively charged, for e.g., ammonium ion. An amino acid under certain conditions would have both positive and negative charges simultaneously in the same molecule. Such a form of amino acid is called
A. Zwitterionic form ✓ Correct
B. Negatively charged form
C. Neutral form
D. Positively charged form
Solution: At its isoelectric pH an amino acid carries both a positive (protonated amino) and a negative (deprotonated carboxyl) charge simultaneously; this dipolar form is called the zwitterionic form.
Q30 — Proteins & Amino Acids · easy
A homopolymer has only one type of building block called monomer repeated 'n' number of times. A heteropolymer has more than one type of monomers. Proteins are heteropolymers made of amino acids. While a nucleic acid like DNA or RNA is made of only 4 types of nucleotide monomers, proteins are made of
A. 40 types of monomers
B. 3 types of monomers
C. 20 types of monomers ✓ Correct
D. Only one type of monomer
Solution: Proteins are heteropolymers built from 20 types of amino acid monomers.