Part 7 — Critical & Complex NEET-level Questions (Q151–175)

Q151.

Which biomolecule is most abundant in living organisms by dry weight?
A. Lipids
B. Proteins ✅
C. Carbohydrates
D. Nucleic acids

Explanation:

A. Lipids: Abundant in membranes, but not most overall.
B. Proteins (Correct): Constitute ~50% of cellular dry weight.
C. Carbohydrates: Energy storage but less by weight.
D. Nucleic acids: Important, but less abundant.

Q152.

Which macromolecule directly determines the structure of proteins synthesized in cells?
A. Carbohydrates
B. Lipids
C. DNA ✅
D. Vitamins

Explanation:

**A. Carbohydrates: energy, not genetic code.
**B. Lipids: membranes, energy.
C. DNA (Correct): Encodes protein sequence via transcription & translation.
**D. Vitamins: cofactors, not coding.

Q153.

Which macromolecule provides maximum energy per gram?
A. Carbohydrates
B. Proteins
C. Lipids ✅
D. Nucleic acids

Explanation:

**A. Carbs: 4 kcal/g.
**B. Proteins: 4 kcal/g.
**C. Lipids (Correct): ~9 kcal/g → most energy-dense.
**D. Nucleic acids: not main energy source.

Q154.

DNA has higher stability than RNA because:
A. DNA has ribose sugar
B. DNA has thymine instead of uracil ✅
C. DNA has fewer hydrogen bonds
D. DNA is single-stranded

Explanation:

**A. Ribose is in RNA, making it less stable.
**B. Correct — thymine provides stability; uracil is more prone to mutation.
**C. DNA has more hydrogen bonds (A–T, G–C).
**D. DNA is double-stranded, not single.

Q155.

Which biomolecule acts as enzyme, genetic material, and structural component depending on type?
A. Protein
B. Lipid
C. Nucleic acid ✅
D. Carbohydrate

Explanation:

**A. Proteins: catalysts & structural but not genetic.
**B. Lipids: membranes & storage, not enzymes/genetic.
C. Nucleic acids (Correct): DNA = genetic, RNA = ribozymes & structural (rRNA, tRNA).
**D. Carbohydrates: energy/structure, not genetic.

Q156.

Km (Michaelis constant) of an enzyme is:
A. Substrate conc. at half Vmax ✅
B. Maximum velocity
C. Enzyme concentration
D. Turnover number

Explanation:

**A. Correct — Km = [S] at ½ Vmax.
**B. Vmax = maximum rate.
**C. Independent of enzyme concentration.
**D. Turnover = molecules converted per second.

Q157.

Competitive inhibition can be overcome by:
A. Increasing substrate concentration ✅
B. Decreasing temperature
C. Adding more enzyme
D. Denaturing enzyme

Explanation:

**A. Correct — high [S] outcompetes inhibitor.
**B. Temp change irrelevant here.
**C. More enzyme: not main solution.
**D. Denaturation destroys enzyme, not helpful.

Q158.

Which enzyme is protein + non-protein part (cofactor) combined?
A. Apoenzyme
B. Holoenzyme ✅
C. Coenzyme
D. Prosthetic group

Explanation:

**A. Apoenzyme: protein only.
B. Holoenzyme (Correct): Apoenzyme + cofactor = active enzyme.
**C. Coenzyme: organic cofactor.
**D. Prosthetic group: tightly bound cofactor.

Q159.

DNA differs from RNA in all EXCEPT:
A. Sugar
B. Nitrogen base
C. Single vs double strandedness
D. Presence of phosphate groups ✅

Explanation:

**A. DNA = deoxyribose; RNA = ribose.
**B. DNA = thymine; RNA = uracil.
**C. DNA mostly double-stranded; RNA single.
**D. Correct — both contain phosphate groups.

Q160.

Enzymes which transfer phosphate groups are:
A. Hydrolases
B. Oxidoreductases
C. Kinases (transferases) ✅
D. Ligases

Explanation:

**A. Hydrolases: break bonds with water.
**B. Oxidoreductases: redox.
**C. Correct — kinases (transferases) add/remove phosphate.
**D. Ligases: join molecules.

Q161.

The enzyme DNA polymerase requires:
A. Template strand ✅
B. RNA primer ✅
C. Free dNTPs ✅
D. All of the above ✅

Explanation:

**A. Template: needed for copying.
**B. RNA primer: provides 3′–OH.
**C. dNTPs: building blocks.
**D. Correct — all required.

Q162.

Which biomolecule serves as primary structural material in plant cell walls?
A. Glycogen
B. Cellulose ✅
C. Chitin
D. Starch

Explanation:

**A. Glycogen: animal storage.
**B. Cellulose (Correct): β-1,4 glucose polymer in walls.
**C. Chitin: fungi/exoskeleton.
**D. Starch: storage, not structure.

Q163.

Which biomolecule acts as buffer in blood plasma?
A. Albumin (protein) ✅
B. Cholesterol
C. Glucose
D. DNA

Explanation:

A. Albumin (Correct): Amphoteric protein, major buffer.
**B. Cholesterol: structural, not buffering.
**C. Glucose: energy, not buffer.
**D. DNA: in nucleus, not buffer.

Q164.

Which bond stabilizes primary structure of proteins?
A. Peptide bond ✅
B. Hydrogen bond
C. Disulfide bond
D. Ionic bond

Explanation:

**A. Correct — peptide bonds link amino acids.
**B. Secondary structure stabilization.
C/D. Tertiary/quaternary stabilization.

Q165.

Which is an example of nucleoprotein?
A. Hemoglobin
B. Ribosome ✅
C. Albumin
D. Collagen

Explanation:

**A. Hemoglobin: chromoprotein.
B. Ribosome (Correct): rRNA + proteins.
C/D. Simple proteins.

Q166.

Non-competitive inhibition occurs when:
A. Inhibitor competes for active site
B. Inhibitor binds allosteric site ✅
C. Substrate concentration reduces
D. Enzyme denatures

Explanation:

**A. That is competitive inhibition.
**B. Correct — non-competitive inhibitor binds elsewhere, alters conformation.
C/D. Not definitions of non-competitive inhibition.

Q167.

Histones are rich in:
A. Aspartic acid and glutamic acid
B. Lysine and arginine ✅
C. Glycine and alanine
D. Valine and leucine

Explanation:

**A. Acidic residues: wrong.
**B. Correct — basic amino acids neutralize DNA’s negative charge.
C/D. Not histone-rich.

Q168.

Which carbohydrate gives reddish-brown with iodine?
A. Cellulose
B. Glycogen ✅
C. Amylose
D. Amylopectin

Explanation:

**A. Cellulose: no iodine reaction.
B. Glycogen (Correct): Gives reddish-brown color.
**C. Amylose: blue color.
**D. Amylopectin: violet color.

Q169.

In Watson–Crick model of DNA, the two strands run:
A. Parallel
B. Antiparallel ✅
C. Crossed randomly
D. Without polarity

Explanation:

**A. Parallel: wrong.
B. Antiparallel (Correct): One 5′→3′, other 3′→5′.
C/D. Not correct.

Q170.

Which biomolecule forms antibodies?
A. Proteins ✅
B. Lipids
C. Carbohydrates
D. Nucleic acids

Explanation:

A. Proteins (Correct): Immunoglobulins are glycoproteins.
**B. Lipids: not defense molecules.
**C. Carbohydrates: structural/energy.
**D. Nucleic acids: information storage.

Q171.

DNA content doubles in which phase of cell cycle?
A. G1
B. S-phase ✅
C. G2
D. M-phase

Explanation:

**A. G1: growth, no DNA replication.
B. S-phase (Correct): DNA replication occurs.
**C. G2: preparation for mitosis.
**D. M-phase: division.

Q172.

Enzymes functioning outside cells are called:
A. Endoenzymes
B. Exoenzymes ✅
C. Allosteric enzymes
D. Isoenzymes

Explanation:

**A. Endoenzymes: inside cells.
B. Exoenzymes (Correct): Secreted enzymes (e.g., digestive).
**C. Allosteric: regulated enzymes.
**D. Isoenzymes: multiple forms of same enzyme.

Q173.

Which molecule acts as genetic material in HIV?
A. DNA
B. RNA ✅
C. Both DNA & RNA
D. Protein

Explanation:

**A. DNA: not initial material.
B. RNA (Correct): Retrovirus, RNA genome → reverse transcription.
C/D. Not correct.

Q174.

Which lipid-derived molecule regulates inflammation?
A. Glycogen
B. Prostaglandins ✅
C. Albumin
D. Hemoglobin

Explanation:

**A. Glycogen: carbohydrate.
B. Prostaglandins (Correct): Derived from arachidonic acid, mediate inflammation.
C/D. Not lipid regulators.

Q175.

Which enzyme catalyzes joining of DNA fragments?
A. DNA polymerase
B. DNA ligase ✅
C. Helicase
D. Primase

Explanation:

**A. DNA polymerase: elongates chain.
B. DNA ligase (Correct): Joins Okazaki fragments.
**C. Helicase: unwinds.
**D. Primase: RNA primers.

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Part 7 — Critical & Complex NEET-level Questions (Q151–175)