Q.43 One molecule of the protein myoglobin contains one atom of iron. A myoglobin
sample was found to contain 0.34% iron. The molecular weight of myoglobin
is __________ π πππβ1 (rounded off to the nearest integer).
(Use 55.9 π πππβ1 as atomic mass of iron)
Myoglobinβs molecular weight is 16441 g/mol, calculated from its 0.34% iron content and one iron atom per molecule using the given atomic mass of 55.9 g/mol.
Introduction to Myoglobin Iron Calculation
Myoglobin molecular weight calculation hinges on its 0.34% iron content, a key CSIR NET Life Sciences question testing
percentage composition and molar mass concepts. With one iron atom per molecule and
atomic mass 55.9 g/mol, students can solve for the proteinβs molecular weight efficiently.
This method applies biochemistry principles to real exam scenarios.
Detailed Step-by-Step Solution
- Take 100 g myoglobin sample: iron mass = 0.34% Γ 100 = 0.34 g.
- One mole of myoglobin contains one mole of Fe = 55.9 g Fe.
- Equation for molar mass (M):
0.34/100 Γ M = 55.9
- Solve for M:
M = (55.9 Γ 100) / 0.34 = 16441.18 β 16441 g/mol
The calculated molecular weight (16441 g/mol) matches standard textbook and
exam reference values, confirming accurate use of the data and rounding method.
Common Errors and Explanations
- Using 56 g/mol for Fe yields ~16471 g/mol (off by ~30 g/mol).
- Forgetting Γ100 in percentage formula underestimates result by a factor of 100.
- Assuming multiple Fe atoms per molecule gives incorrect molecular weight.
Correct use of given 55.9 g/mol ensures the accurate myoglobin molecular mass.
CSIR NET Exam Relevance
This question, often found in IIT JAM or CSIR NET exams, assesses
quantitative biochemistry understanding. It links myoglobinβs heme iron composition to molecular
weight determination, integrating concepts from protein chemistry and enzyme structure.
Mastering such calculations reinforces analytical and conceptual clarity for competitive exams.
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