Part 8 — Analytical, Case-based & Higher-order NEET MCQs (Q176–200)

Part 8 — Analytical, Case-based & Higher-order NEET MCQs (Q176–200)

Q176.

A cell is found to have high levels of ribose and nitrogenous bases adenine, guanine, cytosine, and uracil. Which molecule is being synthesized?
A. DNA
B. RNA ✅
C. Protein
D. Lipid

Explanation:

• A. DNA: Uses deoxyribose and thymine, not ribose/uracil.
• B. RNA (Correct): Ribose + uracil = RNA synthesis.
• **C. Protein: amino acids, not bases.
• **D. Lipid: fatty acids, not bases.

Q177.

A laboratory test reveals a violet color when copper sulfate in alkaline solution is added to a sample. What biomolecule is present?
A. Carbohydrate
B. Protein ✅
C. Lipid
D. Nucleic acid

Explanation:

• **A. Carbohydrate: detected by Molisch/Iodine.
• B. Protein (Correct): Biuret test detects peptide bonds.
• **C. Lipid: Sudan stain.
• **D. Nucleic acid: diphenylamine test.

Q178.

A mutation changes one amino acid in hemoglobin, causing sickle-shaped RBCs. This represents a defect in which protein level?
A. Primary ✅
B. Secondary
C. Tertiary
D. Quaternary

Explanation:

• A. Primary (Correct): Sequence change in β-chain (glutamic acid → valine).
• **B. Secondary/Tertiary: folding, not cause.
• **D. Quaternary: subunit association, not altered directly.

Q179.

Enzyme A has optimum activity at pH 2, enzyme B at pH 8. Where are they most likely found?
A. Both in blood
B. A in stomach, B in intestine ✅
C. A in saliva, B in nucleus
D. Both in mitochondria

Explanation:

• **A. Blood pH ~7.4, unsuitable.
• **B. Correct — pepsin (pH 2, stomach), trypsin (pH 8, intestine).
• C/D. Not matching pH conditions.

Q180.

A polysaccharide gives blue-black color with iodine. Its identity is:
A. Glycogen
B. Starch ✅
C. Cellulose
D. Chitin

Explanation:

• **A. Glycogen: reddish-brown.
• B. Starch (Correct): Blue-black with iodine.
• C/D. No such reaction.

Q181.

If all disulfide bonds in insulin are broken, what is lost first?
A. Primary structure
B. Secondary structure
C. Tertiary structure ✅
D. Sequence of amino acids

Explanation:

• **A. Primary: peptide bonds unaffected.
• **B. Secondary: mostly H-bonds.
• **C. Correct — disulfide bridges stabilize tertiary structure.
• **D. Sequence unaffected.

Q182.

A patient has a deficiency in niacin (Vitamin B3). Which coenzyme will be deficient?
A. FAD
B. NAD⁺ ✅
C. Coenzyme A
D. Biotin

Explanation:

• **A. FAD: from riboflavin.
• B. NAD⁺ (Correct): From niacin, key redox coenzyme.
• **C. CoA: from pantothenic acid.
• **D. Biotin: another vitamin.

Q183.

A solution contains DNA, proteins, and starch. Which test identifies DNA?
A. Biuret
B. Iodine
C. Diphenylamine ✅
D. Molisch

Explanation:

• **A. Biuret: proteins.
• **B. Iodine: starch.
• C. Diphenylamine (Correct): Blue color test for DNA (deoxyribose).
• **D. Molisch: carbohydrates in general.

Q184.

Which lipid abnormality leads to atherosclerosis?
A. High HDL
B. High LDL ✅
C. Low LDL
D. Low cholesterol

Explanation:

• **A. HDL: protective.
• B. LDL (Correct): Excess deposition in arteries.
• C/D. Not risk factors.

Q185.

A researcher isolates an RNA that folds into cloverleaf structure and carries amino acids. It is:
A. mRNA
B. tRNA ✅
C. rRNA
D. hnRNA

Explanation:

• **A. mRNA: linear coding.
• B. tRNA (Correct): Cloverleaf, anticodon + amino acid.
• **C. rRNA: ribosomal.
• **D. hnRNA: precursor to mRNA.

Q186.

In enzyme kinetics, if Vmax remains constant but Km increases, it indicates:
A. Non-competitive inhibition
B. Competitive inhibition ✅
C. Irreversible inhibition
D. No inhibition

Explanation:

• **A. Non-competitive: decreases Vmax.
• B. Competitive (Correct): Km increases, Vmax unchanged.
• **C. Irreversible: enzyme destroyed.
• **D. No inhibition: no change.

Q187.

Which base pair has higher melting temperature (Tm)?
A. A–T
B. G–C ✅
C. A–U
D. Random

Explanation:

• **A. A–T: 2 H-bonds.
• **B. G–C (Correct): 3 H-bonds → higher stability.
• **C. A–U: in RNA, 2 bonds.
• **D. Random: not specific.

Q188.

Which polysaccharide is structurally similar to cellulose but found in fungi?
A. Chitin ✅
B. Starch
C. Glycogen
D. Inulin

Explanation:

• A. Chitin (Correct): β-1,4 polymer of N-acetylglucosamine.
• **B. Starch: α-1,4/α-1,6 glucose.
• **C. Glycogen: animal storage.
• **D. Inulin: fructan in plants.

Q189.

DNA replication requires short RNA primers because:
A. DNA polymerase cannot start synthesis de novo ✅
B. RNA is more stable
C. DNA cannot be replicated otherwise
D. To replace uracil with thymine

Explanation:

• **A. Correct — polymerase requires free 3′–OH group.
• **B. RNA is less stable.
• **C. Too vague.
• **D. Incorrect reason.

Q190.

A patient’s urine sample tested positive with Benedict’s solution. Likely biomolecule present is:
A. Protein
B. Lipid
C. Reducing sugar ✅
D. DNA

Explanation:

• **A. Protein: Biuret test.
• **B. Lipid: Sudan stain.
• C. Reducing sugar (Correct): Glucose, galactose, fructose.
• **D. DNA: diphenylamine test.

Q191.

If cytosine makes up 20% of DNA bases, what is adenine content?
A. 20%
B. 30% ✅
C. 40%
D. 50%

Explanation:

• **A. Wrong: C = G = 20%.
• **B. Correct — A = T, so A + T = 60%, hence A = 30%.
• C/D. Not possible.

Q192.

Which lipid acts as precursor for sex hormones?
A. Cholesterol ✅
B. Palmitic acid
C. Stearic acid
D. Lecithin

Explanation:

• A. Cholesterol (Correct): Precursor of estrogen, testosterone, progesterone.
• B/C. Saturated fatty acids.
• **D. Lecithin: phospholipid.

Q193.

DNA and RNA differ in all EXCEPT:
A. Type of sugar
B. Nitrogenous base
C. Phosphate group ✅
D. Double vs single-strandedness

Explanation:

• **A. DNA = deoxyribose; RNA = ribose.
• **B. DNA = thymine; RNA = uracil.
• **C. Correct — both contain phosphate.
• **D. DNA usually double; RNA single.

Q194.

Enzyme activity declines sharply above optimum temperature because:
A. Active site expands
B. Denaturation of protein structure ✅
C. More substrate formed
D. Cofactor destroyed

Explanation:

• **A. Not mechanism.
• **B. Correct — high heat disrupts H-bonds → denaturation.
• C/D. Not main cause.

Q195.

In sickle-cell anemia, glutamic acid is replaced by valine in β-chain of hemoglobin. This is:
A. Frameshift mutation
B. Missense mutation ✅
C. Nonsense mutation
D. Silent mutation

Explanation:

• **A. Frameshift: insertion/deletion.
• B. Missense (Correct): One amino acid substituted → altered protein.
• **C. Nonsense: premature stop codon.
• **D. Silent: no change in protein.

Q196.

An enzyme works best at 37°C and pH 7. When placed at 60°C and pH 2, its activity drops drastically. Why?
A. Substrate lost
B. Enzyme denatured ✅
C. Product inhibited
D. Cofactor absent

Explanation:

• **A. Substrate not lost.
• **B. Correct — extreme heat & pH denature protein.
• C/D. Not direct cause.

Q197.

Which biomolecule is amphipathic and critical for bilayer formation?
A. Triacylglycerols
B. Phospholipids ✅
C. Sterols
D. Glycogen

Explanation:

• **A. TAG: hydrophobic.
• B. Phospholipids (Correct): Hydrophilic head + hydrophobic tails.
• **C. Sterols: help fluidity.
• **D. Glycogen: carbohydrate.

Q198.

If DNA has 40% GC content, what is AT content?
A. 40%
B. 60%
C. 50%
D. 60% ÷ 2 = 30% each ✅

Explanation:

• GC = 40%, so AT = 60%.
• Hence A = 30%, T = 30% (Correct).

Q199.

Which molecule is NOT a polysaccharide?
A. Glycogen
B. Cellulose
C. Inulin ✅
D. Chitin

Explanation:

• **A. Glycogen: glucose polymer.
• **B. Cellulose: glucose polymer.
• C. Inulin (Correct): Fructan, not glucose-based polysaccharide.
• **D. Chitin: N-acetylglucosamine polymer.

Q200.

Which enzyme catalyzes RNA synthesis using DNA as template?
A. DNA polymerase
B. RNA polymerase ✅
C. Reverse transcriptase
D. Primase

Explanation:

• **A. DNA polymerase: DNA synthesis.
• B. RNA polymerase (Correct): Transcribes RNA from DNA.
• **C. Reverse transcriptase: RNA → DNA.
• **D. Primase: synthesizes RNA primers.

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