Q.What would be the molar concentration of human DNA in a human cell? Consult your teacher.

The molar concentration of human DNA in a human cell is not a fixed number you can look up in a table — it depends on the cell type and its stage in the cell cycle. However, we can estimate it using NCERT-based reasoning.

First, recall that a typical human diploid cell contains about 6.6 picograms of DNA (the 2C value, which is the DNA content after S phase but before cell division). This mass corresponds to roughly 6 × 10⁹ base pairs. Using the average molecular mass of a base pair (about 660 g/mol), the total number of moles of DNA in one cell is:

• Mass of DNA = 6.6 × 10⁻¹² g
• Molar mass of one DNA molecule (the entire genome) ≈ 6 × 10⁹ bp × 660 g/mol per bp ≈ 4 × 10¹² g/mol
• Moles of DNA per cell = (6.6 × 10⁻¹² g) / (4 × 10¹² g/mol) ≈ 1.65 × 10⁻²⁴ mol

Now, the volume of a typical human cell is about 1–2 picolitres (1 pL = 10⁻¹² L). Taking 1 pL as a round figure:

• Concentration = moles / volume = (1.65 × 10⁻²⁴ mol) / (10⁻¹² L) = 1.65 × 10⁻¹² mol/L = 1.65 pM …

To understand the molar concentration of human DNA in a human cell, we first need to grasp what is being measured. A human cell contains a diploid genome — that is, two sets of chromosomes, one from each parent. The total length of DNA in a single human cell is about 2 meters, wound tightly into the nucleus. But concentration is about amount per volume, not just length.

The NCERT textbook for Class 11 Biology (Chapter 8: Cell: The Unit of Life) tells us that the human genome has approximately 3.3 × 10⁹ base pairs per haploid set. Since a diploid cell has two such sets, the total DNA content is about 6.6 × 10⁹ base pairs. Each base pair has an average molecular weight of about 660 daltons (or grams per mole). So the mass of DNA in one diploid cell is roughly:

6.6 × 10⁹ base pairs × 660 g/mol per base pair = about 4.4 × 10¹² g/mol for the whole genome.

But that’s the molar mass of the entire DNA molecule — not the concentration. To find molar concentration, we need to know how many moles of DNA are in a cell, and the volume of that cell.

The amount of DNA in a single human cell is about 6 picograms (6 × 10⁻¹² grams). Using the molar mass above, the number of moles of DNA per cell is:

6 × 10⁻¹² g ÷ 4.4 × 10¹² g/mol ≈ 1.36 × 10⁻²⁴ moles.

That’s an incredibly tiny number — less than a billionth of a billionth of a mole.

Now, the volume of a typical human cell is roughly 1 to 4 picoliters (1 picoliter = 10⁻¹² liters). For a mid-sized cell, say 2 picoliters, the molar concentration would be:

(1.36 × 10⁻²⁴ moles) ÷ (2 × 10⁻¹² liters) = 6.8 × 10⁻¹³ M, or about 0.68 picomolar. …

Alternative Approach: A Clean Dimensional-Analysis Walkthrough

The prose answers already estimate a value; here is the same calculation laid out as an

explicit unit-by-unit chain, which is the technique to reuse for any "estimate a

concentration from mass and volume" biology question.

Step 1: State the given/known quantities.

Mass of DNA per diploid human cell ≈ 6-7 picograms (2C value). Approximate diploid

genome size ≈ 6.6x10^9 base pairs. Average molecular weight per base pair ≈ 650-660

grams/mole. Typical human cell volume ≈ 1-4 picolitres.

Step 2: Convert base pairs to a molar mass for the whole genome.

(6.6x10^9 base pairs) x (~660 g/mol per base pair) ≈ 4-4.4x10^12 g/mol for one complete

genome-sized DNA molecule.

Step 3: Convert mass of DNA in the cell to moles.

moles = mass / molar mass ≈ (6-7x10^-12 g) / (4-4.4x10^12 g/mol) ≈ 1.4-1.7x10^-24 mol.

Step 4: Divide by cell volume to get molar concentration.

concentration = moles / volume(in litres). Using 1 picolitre (=10^-12 L): …