The Egg That Will Not Uncook
An egg white turns from clear liquid to opaque solid when cooked and never turns back, though no covalent bond in its protein chains has broken.
What changed, if the chains are intact?
Page 1
Science · Honors Biology
Chapter 1: Biochemistry
The sequence decides the shape, and the shape is the function.
An egg white turns from clear liquid to opaque solid when cooked and never turns back, though no covalent bond in its protein chains has broken.
What changed, if the chains are intact?
Make your guess to turn the page.
Still to come: 11 pages · Lab · Words to Know · What We Learned · 4 questions · Explain It in Writing · Open Questions
The idea this lesson is working on — Students think a denatured protein is simply unfolded and should refold on cooling. The book sets Anfinsen’s dilute enzyme, which does refold, against a crowded egg white, which aggregates. Ask: what did Anfinsen’s test tube have that the egg does not? The idea to reach is a race between refolding and aggregation, with the peptide bonds intact throughout.
Sequence decides shape, shape is function — Pauling and Corey’s peptide geometry (C–N about 1.32 Å against 1.47 Å for a single bond) came from small-molecule crystal structures. Their 1951 alpha helix (3.6 residues, 5.4 Å pitch) was built from it before any protein structure was solved. Anfinsen’s refolding work ran through the late 1950s and 1960s; he shared the 1972 Nobel Prize in Chemistry.
Denaturation is loss of shape, not of sequence — Heat and pH disrupt the interactions holding the fold without breaking peptide bonds. Sickle-cell hemoglobin shows the other side: one substitution, glutamic acid to valine at position 6 of the beta chain, puts a nonpolar patch on the surface. The molecules then polymerize into fibers.