The protein concentration in the mammalian cell is 240 mg/mL, corresponding to option (D).

Step-by-Step Calculation

First, calculate the total mass of the cell using its density and volume: total mass = density × volume = 1.2 g/mL × 4 × 10⁻⁹ mL = 4.8 × 10⁻⁹ g.​
Protein mass is 20% of the total mass: 0.20 × 4.8 × 10⁻⁹ g = 9.6 × 10⁻¹⁰ g.​
Protein concentration = (protein mass / volume) × 1000 = (9.6 × 10⁻¹⁰ g / 4 × 10⁻⁹ mL) × 1000 mg/g = 240 mg/mL.​

Option Analysis

• (A) 60: This results from using 5% protein content instead of 20%, underestimating the fraction.​

• (B) 600: This assumes 50% protein content or doubles the correct mass calculation.​

• (C) 166: This divides total mass by volume without the protein percentage adjustment.​

• (D) 240: Matches the precise calculation using given values, consistent with typical cell protein densities around 200-300 mg/mL.​

Introduction (with Key Phrase: “mammalian cell protein concentration”)
Mammalian cell protein concentration is a key concept in cell biology for CSIR NET Life Sciences exams, where cells typically contain 20% protein by net weight. This article solves the exact problem: with cell density 1.2 g/mL and volume 4×10⁻⁹ mL, find protein concentration in mg/mL. Understanding this calculation helps master quantitative cell biology questions.​

Problem Background

Typical mammalian cells have protein occupying 20-30% of dry mass, with densities around 1.1-1.4 g/mL due to protein-water balance. The given values align with standard models for exam problems.​

Detailed Solution

Total cell mass = 1.2 × 4×10⁻⁹ = 4.8×10⁻⁹ g.
Protein mass = 20% × 4.8×10⁻⁹ = 9.6×10⁻¹⁰ g.
Concentration = (9.6×10⁻¹⁰ / 4×10⁻⁹) × 1000 = 240 mg/mL.​

Why 240 mg/mL Fits Real Cells

This value matches reported ranges (160-310 mg/mL protein) for mammalian cells like rat liver or muscle. Lower values occur in specialized cells like red blood cells.​

Exam Tips for CSIR NET

• Always convert units consistently (g to mg via ×1000).

• Verify protein % applies to total wet weight here.​

• Practice similar problems on cell composition.​