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Protein History — Identify the first protein whose complete three-dimensional tertiary structure was determined by X-ray crystallography.

Difficulty: Easy

Lysozyme
Myoglobin
Pancreatic ribonuclease
Pancreatic DNase
Insulin

Correct Answer: Myoglobin

Explanation:

Introduction:
Determining the first complete protein structure was a landmark in structural biology, validating methods of X-ray crystallography and revealing how amino acid sequence folds into 3D form.

Given Data / Assumptions:

X-ray crystallography was the key method used in early structural determinations.
Historical precedence matters; sequencing and structure are different accomplishments.
Several candidate proteins were characterized around the same era.

Concept / Approach:
Differentiate between 'first sequenced protein' and 'first solved 3D structure'. Insulin was first sequenced, but the first tertiary structure solved at atomic resolution was for myoglobin.

Step-by-Step Solution:

1) Insulin: first sequenced, not the first solved 3D structure.2) Myoglobin: first complete 3D structure solved by John Kendrew and colleagues.3) Other listed enzymes (lysozyme, ribonuclease, DNase) were solved later or were not the first.

Verification / Alternative check:
Historical records in structural biology consistently cite myoglobin as the first complete protein structure, followed closely by hemoglobin.

Why Other Options Are Wrong:

a, c, d) Important proteins but not the first solved in 3D.e) Insulin is historically notable for sequencing, not first structure.

Common Pitfalls:
Conflating 'first sequenced' with 'first structurally solved' or assuming enzymatic prominence correlates with historical order.

Protein History — Identify the first protein whose complete three-dimensional tertiary structure was determined by X-ray crystallography.

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