= Solution
A rising <force> branch means that an already exposed <polypeptide> segment is being stretched while the remaining structure resists further extraction. At a <force> peak a structural barrier is crossed; <protein denaturation> or release of additional chain increases the available <polymer contour length>, so the <force> falls at almost the same imposed separation. Stretching then loads the next remaining barrier. The sawtooth pattern therefore reports a sequence of mechanically resistant intermediates, not a regular <spring> oscillation. The <cantilever> deflection gives <force>, while its own deformation must be removed from the imposed separation to infer molecular extension.
A <membrane protein> also requires work to disrupt membrane anchoring, helix packing and contacts with <lipids> or neighboring <molecules>. The retinal-containing interior contributes a bulky, specifically packed scaffold; exposing chain must overcome these <steric hindrance> as well as <hydrogen bond> and <electrostatic interactions>. A <force> peak need not correspond one-to-one to one complete helix, and its height depends on loading rate and pathway, not just an equilibrium folding <Gibbs free energy>.
Salt changes <electrostatic screening> and specific <ion> binding. Screening can reduce either repulsion or attraction, so “more salt always weakens the <protein>” is false. The primary study underlying these kinds of traces identifies relatively salt-insensitive <steric hindrance> around the <retinal> and additional salt-sensitive barriers. Its interpretation associates some added barriers with screening of destabilizing electrostatic repulsion. The supplied traces likewise show a changed set of intermediate peaks, rather than a uniform rescaling of one curve.https://pmc.ncbi.nlm.nih.gov/articles/PMC1959538/[2007 primary study, Results: Unfolding bR from PM cytoplasmic side; Discussion: steric and electrostatic contributions]{ref}
Exact assignment of every arrow to a residue requires structural and statistical information beyond one representative trace. No such assignment is inferred here. The printed reference to \b[<titin>] in the following paragraph is inconsistent with the stated specimen and the membrane-protein traces; the physical interpretation here concerns <bacteriorhodopsin>, while the worm-like-chain expression is a generic <polymer> approximation.
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