Q.7 If molecular weight of a protein is gm per mole. would be the number of amino acids in the
protein. assuming mean molecular weight of an amino acid to be 110 gm per mole ?
1. 2200
2. 2000
3. 3300
4. 200

If the protein’s molecular weight is 220,000 g/mol (inferred from options and standard approximation), it contains approximately 2000 amino acids, using the mean residue weight of 110 g/mol. Number of amino acids ≈ protein MW / 110.

Question Solution

The query appears incomplete (“gm per mole” likely means X g/mol, with X=220,000 as per option math). Standard calculation: Divide protein molecular weight by average amino acid residue mass (110 Da, accounting for -H₂O loss in peptides). For 220,000 g/mol: 220,000 / 110 = 2000.

Option Analysis

• Option 1: 2200
  Incorrect. Yields MW = 2200 × 110 = 242,000 g/mol (too high if assuming ~220k target).

• Option 2: 2000
  Correct. 2000 × 110 = 220,000 g/mol, standard approximation for many proteins (e.g., 288 residues ≈32 kDa).

• Option 3: 3300
  Incorrect. 3300 × 110 = 363,000 g/mol (excessive for typical query assumption).

• Option 4: 200
  Incorrect. 200 × 110 = 22,000 g/mol (small protein, e.g., oxytocin-like).​

Estimating the number of amino acids in a protein from its molecular weight is a fundamental biochemistry calculation, using the mean residue mass of 110 g/mol after peptide bond formation. For a protein molecular weight of 220,000 g/mol, divide by 110 to get approximately 2000 amino acids.

Calculation Method

Average free amino acid MW ≈128 Da; subtract 18 Da H₂O per bond yields 110 Da/residue. Formula: n = MW_protein / 110. Example: 288 residues ≈ 31,680 Da (≈32 kDa).

Applications in Research

Used in SDS-PAGE predictions, purification, and exam questions. Tools like ExPASy refine via sequence; approximations suffice for rough estimates in molecular biology.

Exam Tips

Assume 110 Da standard; verify with options (e.g., 2000 fits 220 kDa). Post-modifications (glycosylation) increase actual MW.