GATE — Life Sciences (XL) with Section U Food Technology · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersCarbohydrates, proteins, lipids, enzymes and metabolism at the level a dairy chemist and microbiologist needs before studying milk itself.
In the exams: Background for ICAR AICE subject 34 Units 1–3 and GATE XL-Q/XL-U Section 1
How our questions for GATE spread across the units of Biochemistry for Dairy Science. Difficulty: 12 easy, 57 medium, 0 hard.
| Carbohydrate structure and reactions | 8 | |
| Enzymes: classification and Michaelis-Menten kinetics | 8 | |
| Lipid and amino acid metabolism | 8 | |
| Nucleic acids and protein synthesis | 8 | |
| Vitamins as coenzymes and minerals | 8 | |
| Enzyme inhibition and regulation | 7 | |
| Glycolysis, TCA cycle and oxidative phosphorylation | 7 | |
| Amino acids, peptides and protein structure | 6 | |
| Water, pH and buffers | 5 | |
| Lipid classes and fatty acids | 4 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
The interconversion of α- and β-anomers of lactose in solution until equilibrium is reached is called:
C. Mutarotation
Through the open-chain form the anomers interconvert, changing optical rotation until equilibrium (about 37% α, 63% β for lactose at room temperature).
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Glycine has pKa values of 2.34 (carboxyl) and 9.60 (amino). What is its isoelectric point?
A. 5.97
pI = (2.34 + 9.60)/2 = 5.97. 11.94 is the sum without halving.
Further reading: Nelson and Cox, Lehninger Principles of Biochemistry
An α-helix contains how many amino acid residues per turn?
A. 3.6
The right-handed α-helix has 3.6 residues per turn and a rise of 0.54 nm per turn. 10.5 is the number of base pairs per turn of B-DNA.
Further reading: Nelson and Cox, Lehninger Principles of Biochemistry
Which pair are the essential fatty acids for humans?
B. Linoleic (18:2 n-6) and α-linolenic (18:3 n-3)
Humans cannot introduce double bonds beyond Δ9, so n-6 and n-3 parents must come from the diet.
Further reading: Nelson and Cox, Lehninger Principles of Biochemistry
β-Galactosidase hydrolysing lactose in milk slows down as the reaction proceeds partly because:
C. Galactose, a product, competitively inhibits the enzyme
Galactose resembles the galactosyl part of lactose and competes for the active site of many β-galactosidases. Substrate depletion also reduces the rate.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Why must lactic acid bacteria reduce pyruvate to lactate rather than simply accumulate pyruvate?
C. To regenerate NAD⁺ so that glycolysis can continue
Glyceraldehyde 3-phosphate dehydrogenase needs NAD⁺; without respiration, reducing pyruvate is the way to reoxidise NADH. The LDH step itself makes no ATP.
Further reading: Nelson and Cox, Lehninger Principles of Biochemistry
Antibiotics such as tetracyclines inhibit bacteria selectively because they act on:
A. Bacterial 70S ribosomes, which differ from 80S ones
Structural differences between 70S and 80S ribosomes allow selective inhibition of bacterial protein synthesis.
Further reading: Nelson and Cox, Lehninger Principles of Biochemistry
The light-induced off-flavour of milk displayed under fluorescent lighting is initiated by which vitamin acting as a photosensitiser?
C. Riboflavin
Riboflavin absorbs light and generates reactive species that oxidise methionine to methional and attack lipids; riboflavin itself is destroyed.
Further reading: Fox et al., Dairy Chemistry and Biochemistry
Biotin acts as the coenzyme of which type of reaction?
D. Carboxylation
Biotin carries activated CO₂ in carboxylases such as acetyl-CoA carboxylase and pyruvate carboxylase.
Further reading: Nelson and Cox, Lehninger Principles of Biochemistry
Magnesium is required by virtually every enzyme that uses ATP because:
C. The true substrate is the magnesium–ATP complex
Mg²⁺ binds the phosphates of ATP, shielding charge and positioning it for catalysis.
Further reading: Nelson and Cox, Lehninger Principles of Biochemistry
Ten here, 69 in the app. The Laisha app has every practice question we have written to GATE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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