Online Test — Biomolecules
20 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 20
Which of the following is a monosaccharide?
Sucrose
Maltose
Glucose
Starch
Explanation: Glucose cannot be hydrolysed further; sucrose and maltose are disaccharides and starch is a polysaccharide.
Question 2 of 20
Sucrose is a non-reducing sugar because:
it has no carbon
both anomeric carbons are in the glycosidic bond
it is a polysaccharide
it contains nitrogen
Explanation: With both anomeric carbons tied up in the glycosidic linkage, no free aldehyde/keto group remains, so it cannot reduce Tollens'/Fehling's.
Question 3 of 20
Glucose mainly exists in solution as a:
five-membered furanose ring
six-membered pyranose ring
straight chain only
three-membered ring
Explanation: The C5–OH adds to the C1 aldehyde to give the stable six-membered pyranose ring.
Question 4 of 20
The anomeric carbon of glucose is:
C2
C5
C1
C6
Explanation: C1, the former aldehyde carbon, becomes a new chiral centre on ring closure, giving the α and β anomers.
Question 5 of 20
Cellulose is composed of glucose units joined by:
α-1,4 links
α-1,6 links
peptide links
β-1,4 links
Explanation: β-1,4 glycosidic links give rigid linear fibres that human enzymes cannot hydrolyse.
Question 6 of 20
An α-amino acid in the solid state exists chiefly as a:
neutral molecule
zwitterion
free radical
carbanion
Explanation: The proton shifts from –COOH to –NH2, giving the dipolar zwitterion +H3N–CHR–COO−.
Question 7 of 20
The isoelectric point of an amino acid is the pH at which it:
is fully protonated
has maximum positive charge
has zero net charge
decomposes
Explanation: At the pI the species is almost entirely the zwitterion with net charge zero and does not migrate in an electric field.
Question 8 of 20
The bond between two amino acids in a protein is called a:
glycosidic bond
phosphodiester bond
hydrogen bond
peptide bond
Explanation: The –COOH of one amino acid condenses with the –NH2 of another, forming the amide (peptide) link –CO–NH–.
Question 9 of 20
The α-helix of a protein is stabilised by:
disulphide bonds only
intramolecular hydrogen bonds
peptide bonds between sheets
ionic bonds only
Explanation: Backbone C=O and N–H groups within the same chain form H-bonds that hold the right-handed helix.
Question 10 of 20
Coagulation of egg white on boiling is an example of:
hydrolysis
denaturation
esterification
saponification
Explanation: Heat disrupts the weak forces holding the 2°/3° structure (denaturation); peptide bonds stay intact.
Question 11 of 20
Enzymes are highly specific catalysts that are chemically:
carbohydrates
globular proteins
lipids
minerals
Explanation: Almost all enzymes are globular proteins whose shaped active site binds only the matching substrate.
Question 12 of 20
Which vitamin is fat-soluble?
Vitamin C
Vitamin B1
Vitamin D
Vitamin B12
Explanation: Vitamins A, D, E and K are fat-soluble; B-complex and C are water-soluble.
Question 13 of 20
Rickets in children is caused by deficiency of vitamin:
A
C
D
K
Explanation: Vitamin D is needed for calcium absorption and bone formation; its deficiency causes rickets (children) and osteomalacia (adults).
Question 14 of 20
Night blindness results from a deficiency of vitamin:
A
B1
C
E
Explanation: Vitamin A (retinol) is essential for the visual pigment; its deficiency causes night blindness and xerophthalmia.
Question 15 of 20
The pentose sugar in RNA is:
2-deoxyribose
ribose
glucose
galactose
Explanation: RNA contains β-D-ribose, whereas DNA contains 2-deoxyribose.
Question 16 of 20
In DNA, guanine forms a complementary pair with:
adenine
thymine
uracil
cytosine
Explanation: G≡C pairing uses three hydrogen bonds; A=T uses two; pairing is always purine–pyrimidine.
Question 17 of 20
A nucleoside consists of:
base + phosphate
sugar + phosphate
base + sugar
base + sugar + phosphate
Explanation: Nucleoside = base + sugar; adding a phosphate to C5′ gives a nucleotide.
Question 18 of 20
The base found in RNA but not in DNA is:
thymine
uracil
adenine
guanine
Explanation: RNA uses uracil where DNA uses thymine; the other three bases are common to both.
Question 19 of 20
Which disaccharide on hydrolysis gives glucose and galactose?
sucrose
maltose
lactose
cellobiose
Explanation: Lactose (milk sugar) hydrolyses to β-D-galactose and D-glucose; it is a reducing sugar.
Question 20 of 20
Insulin, which lowers blood glucose, is an example of a:
vitamin
protein hormone
polysaccharide
nucleic acid
Explanation: Insulin is a peptide/protein hormone secreted by the pancreas that lowers blood glucose.