Q66.Which of the following statements together describe the integral membrane proteins:

A. Form main component of the biological membranes
B. Are soluble in aqueous solutions
C. Mostly composed of polar amino acids and are lysine rich
D. Are soluble in sodium dodecyl sulphate (SDS)
E. Form aggregates in aqueous solutions

Choose the correct answer from the option given below:

(1) A, D, E Only
(2) C, D, E Only
(3) B, C, D Only
(4) A, D, E Only

Integral membrane proteins are major membrane components with hydrophobic transmembrane domains, soluble in SDS but insoluble in water. The correct answer is option (4): A, D, E only.

Statement Analysis

A. Form main component of the biological membranes. Correct—integral membrane proteins comprise 20-80% of membrane mass (vs. lipids), essential for transport, signaling, recognition.

B. Are soluble in aqueous solutions. Incorrect—hydrophobic transmembrane helices/barrels embed in lipid bilayer; water extraction causes aggregation.

C. Mostly composed of polar amino acids and are lysine rich. Incorrect—transmembrane regions rich in hydrophobic residues (Leu, Ile, Val, Phe); polar/charged (Lys, Arg) enriched at interfaces, following “positive-inside rule.”

D. Are soluble in sodium dodecyl sulphate (SDS). Correct—SDS denatures proteins, coats with negative charge, solubilizes hydrophobic domains for SDS-PAGE.​

E. Form aggregates in aqueous solutions. Correct—lacking lipid environment, hydrophobic domains drive irreversible aggregation.

Option Breakdown

• (1) A, D, E Only: Correct—captures defining traits (abundant, SDS-soluble, aggregate in water).

• (2) C, D, E Only: Wrong—C contradicts hydrophobic composition.

• (3) B, C, D Only: Wrong—B, C both false.

• (4) A, D, E Only: Matches (1)—exam lists duplicate for trickery, but both valid.

Integral membrane proteins form main component of the biological membranes, embedded via hydrophobic α-helices/β-barrels spanning phospholipid bilayers.

Key Properties

• Abundant: 50-70% membrane protein mass in plasma membranes.

• Hydrophobic core: Non-polar residues (Ile, Leu, Val, Phe) dominate transmembrane spans (∼20-25 residues/helix).

• SDS soluble: Detergent disrupts lipid interactions, linearizes for electrophoresis.

• Water insoluble: Aggregate without amphipathic environment.

Structural Types

• Polytopic: Multi-span (GPCRs: 7TM helices).

• Bitopic: Single-span (Type I/II receptors).

• Monotopic: Membrane-associated (one face).

Exam Focus

CSIR/NEET tests hydrophobic vs. peripheral distinction. A/D/E define integral proteins; B/C describe soluble/peripheral.