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Biomolecules — NEET Biology MCQs with Solutions
Free NEET Biology Biomolecules MCQs with step-by-step solutions covering Chemical Composition & Metabolites, Proteins & Amino Acids, Carbohydrates & Nucleic Acids, Structure of Proteins & Metabolism, Enzymes. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — Chemical Composition & Metabolites · easy · theory
Compounds with molecular weight less than ~1000 Da found in the acid-soluble pool are called:
A. Polymers only
B. Macromolecules
C. Micromolecules (e.g. sugars, amino acids) ✓ Correct
D. Enzymes
Solution: Micromolecules (mol. wt < 1000 Da) form the acid-soluble pool; macromolecules (> 10 kDa) are in the acid-insoluble fraction.
Q2 — Chemical Composition & Metabolites · easy · theory
Alkaloids, flavonoids, rubber and essential oils are examples of:
A. Primary metabolites
B. Secondary metabolites ✓ Correct
C. Enzymes
D. Biomacromolecules
Solution: Secondary metabolites have no obvious direct role in normal physiology but are useful (drugs, pigments, defence).
Q3 — 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.
Q4 — 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.
Q5 — Carbohydrates & Nucleic Acids · easy · theory
The most abundant carbohydrate (and organic macromolecule) in nature, forming plant cell walls, is:
A. Cellulose ✓ Correct
B. Chitin
C. Starch
D. Glycogen
Solution: Cellulose (a homopolymer of glucose) is the most abundant polysaccharide; it forms plant cell walls.
Q6 — Carbohydrates & Nucleic Acids · easy · theory
The nitrogenous bases in DNA are adenine, guanine, cytosine and:
A. Thymine ✓ Correct
B. Xanthine
C. Uracil
D. Hypoxanthine
Solution: DNA contains thymine; in RNA, uracil replaces thymine.
Q7 — Structure of Proteins & Metabolism · easy · theory
The linear sequence of amino acids in a polypeptide is its ______ structure:
A. Tertiary
B. Quaternary
C. Primary ✓ Correct
D. Secondary
Solution: Primary structure = amino acid sequence; the first amino acid (N-terminal) and last (C-terminal) mark the ends.
Q8 — Structure of Proteins & Metabolism · easy · theory
The sum total of all the chemical reactions occurring in a cell/body is called:
A. Catalysis
B. Osmosis
C. Metabolism ✓ Correct
D. Diffusion
Solution: Metabolism includes anabolic (build-up) and catabolic (break-down) reactions; no metabolite exists in isolation.
Q9 — Enzymes · easy · theory
Enzymes are biological catalysts that speed up reactions by:
A. Lowering the activation energy ✓ Correct
B. Being consumed in the reaction
C. Changing the equilibrium constant
D. Raising the activation energy
Solution: Enzymes lower the activation energy of a reaction; they are not used up and do not alter the equilibrium.
Q10 — Enzymes · easy · theory
The specific region of an enzyme where the substrate binds is the:
A. Allosteric site only
B. Cofactor
C. Active site ✓ Correct
D. Backbone
Solution: The active site is a crevice/pocket shaped to fit specific substrate(s) forming an enzyme–substrate complex.
Q11 — Chemical Composition & Metabolites · easy · numerical
Which of the following would be recovered from the acid-INSOLUBLE fraction when a tissue is ground with trichloroacetic acid?
A. Glucose
B. A free nucleotide
C. A free amino acid
D. Cellulose ✓ Correct
Solution: Cellulose is a polysaccharide macromolecule and settles in the acid-insoluble pool; glucose, nucleotides and free amino acids are small acid-soluble metabolites.
Q12 — Chemical Composition & Metabolites · easy · numerical
Excluding water, which class of compounds forms the single largest fraction of a cell's weight?
A. Proteins ✓ Correct
B. Nucleic acids
C. Carbohydrates
D. Lipids
Solution: In the average chemical composition of a cell, proteins (~10–15%) exceed carbohydrates (~3%), lipids (~2%) and nucleic acids (~5–7%) once water is excluded.
Q13 — Chemical Composition & Metabolites · easy · numerical
When a piece of living tissue is completely burnt, the residue (ash) that remains represents the:
A. inorganic elements and minerals such as calcium and phosphorus ✓ Correct
B. total carbohydrate content of the cell
C. nucleic acids of the cell
D. proteins and lipids of the cell
Solution: On complete combustion the organic compounds are lost as volatile gases (CO₂, water vapour, etc.), leaving behind the inorganic mineral elements as ash.
Q14 — Chemical Composition & Metabolites · easy · numerical
Biomacromolecules are distinguished from micromolecules chiefly because macromolecules have molecular weights that are:
A. in the range of ten thousand daltons and above ✓ Correct
B. less than that of a water molecule
C. exactly equal to eight hundred daltons
D. always less than one thousand daltons
Solution: Macromolecules (proteins, nucleic acids, polysaccharides) have molecular weights of ~10,000 Da and above, whereas micromolecules of the acid-soluble pool are below ~1000 Da.
Q15 — 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.
Q16 — 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.
Q17 — 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.
Q18 — 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.
Q19 — Carbohydrates & Nucleic Acids · easy · numerical
Which of the following is a monosaccharide?
A. Sucrose
B. Fructose ✓ Correct
C. Maltose
D. Starch
Solution: Fructose is a single sugar unit (monosaccharide); sucrose and maltose are disaccharides and starch is a polysaccharide.
Q20 — Carbohydrates & Nucleic Acids · easy · numerical
The disaccharide sucrose is made up of:
A. glucose and galactose
B. fructose and galactose
C. glucose and glucose
D. glucose and fructose ✓ Correct
Solution: Sucrose (table sugar) is formed by a glycosidic bond between glucose and fructose.
Q21 — Carbohydrates & Nucleic Acids · easy · numerical
A nucleoside consists of a nitrogenous base joined to a sugar, but it lacks:
A. the nitrogenous base
B. the pentose sugar
C. a hydroxyl group
D. a phosphate group ✓ Correct
Solution: A nucleoside is base + sugar; adding a phosphate group converts it into a nucleotide.
Q22 — Carbohydrates & Nucleic Acids · easy · numerical
Which of the following is a pyrimidine base?
A. Both adenine and guanine
B. Adenine
C. Guanine
D. Cytosine ✓ Correct
Solution: Cytosine (with thymine and uracil) is a single-ringed pyrimidine; adenine and guanine are double-ringed purines.
Q23 — Structure of Proteins & Metabolism · easy · numerical
The regular local coiling or folding of a polypeptide chain into helices or sheets represents its ______ structure:
A. tertiary
B. primary
C. quaternary
D. secondary ✓ Correct
Solution: Secondary structure refers to regular patterns such as the α-helix and β-pleated sheet formed by the polypeptide backbone.
Q24 — Structure of Proteins & Metabolism · easy · numerical
The end of a polypeptide that is conventionally written first and carries a free amino group is called the:
A. N-terminal (amino terminal) ✓ Correct
B. phosphate terminal
C. C-terminal (carboxyl terminal)
D. R-terminal
Solution: By convention the first amino acid, bearing the free –NH₂ group, is the N-terminal (left) end; the last is the C-terminal end.
Q25 — Structure of Proteins & Metabolism · easy · numerical
Which level of protein organisation is essential for a protein to carry out biological functions such as catalysis?
A. The linear order of amino acids only
B. The peptide bond alone
C. The tertiary (three-dimensional) structure ✓ Correct
D. The primary sequence alone
Solution: The functional properties of a protein depend on its overall three-dimensional (tertiary) folding, which creates the active shape.
Q26 — Structure of Proteins & Metabolism · easy · numerical
Metabolic reactions in the body rarely occur in isolation; instead they are linked in ordered sequences called:
A. glycosidic chains
B. metabolic pathways ✓ Correct
C. isoelectric points
D. zwitterions
Solution: Metabolites are converted into one another through chains of enzyme-catalysed steps known as metabolic pathways.
Q27 — Enzymes · easy · numerical
Chemically, almost all enzymes are:
A. simple inorganic ions
B. lipids
C. proteins ✓ Correct
D. carbohydrates
Solution: Almost all enzymes are proteins (a few RNA molecules, ribozymes, also act catalytically), giving them their specific three-dimensional shapes.
Q28 — Enzymes · easy · numerical
The model proposing that an enzyme's active site is exactly complementary in shape to its substrate, like a lock and its key, is the:
A. induced-fit model
B. fluid-mosaic model
C. sliding-filament model
D. lock-and-key model ✓ Correct
Solution: The lock-and-key model assumes a rigid active site precisely matching the substrate; the induced-fit model allows the site to change shape on binding.
Q29 — Enzymes · easy · numerical
Many coenzymes required for enzyme activity are derived from:
A. minerals such as zinc
B. simple monosaccharides
C. fatty acids
D. vitamins ✓ Correct
Solution: Coenzymes are organic cofactors, and many of them are derived from vitamins (e.g. NAD from niacin).
Q30 — Enzymes · easy · numerical
The IUB system divides enzymes into how many major classes?
A. Four
B. Ten
C. Six ✓ Correct
D. Three
Solution: Enzymes are grouped into six classes: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases.