Ubiquitin is a small protein attached to other proteins in cellular sorting and regulation, including targeting many substrates to a proteasome.

A proteasome is a protein complex that carries out proteolysis; unlike a lysosome, it has no surrounding lipid bilayer.

Hemoglobin is an oxygen-binding protein; its oxygenation can supply a spectroscopic molecular oxygen readout, as in the early Hill reaction work.

A ribonucleoprotein is an association of RNA with proteins.

Nucleoplasmin is a nuclear protein used in the nuclear pore localization experiment.

An importin is a protein involved in selective import through a nuclear pore complex.

An electron carrier protein in the mitochondrial respiratory chain.

A peptide comprises amino acid residues joined through peptide bonds.

Ovalbumin is the protein target in the historical binding comparison discussed under Papain digestion of IgG.

A whey protein used as a model solute in studies of protein association and transport. Its effective electric charge, association state and hydrodynamic radius depend on solution conditions. In a specified spherical-particle model, its electrophoretic mobility and sedimentation speed depend on its charge and buoyant mass through the same Stokes drag law.

Polymer physics connects the conformations and motion of long molecules to the properties of a material. A polymer can change shape through many segment rotations while its chemical backbone remains intact. This makes the competition between flow and relaxation important: the same chain can behave as a coil in one experiment and an extended object in another. Soft matter includes both these flexible structures and liquid crystals, whose orientational order produces a different route to strong mechanical and optical response.

Polyethylene glycol is a water-soluble polymer with repeating ethylene oxide units. Nonadsorbing dissolved chains can cause a depletion force between larger colloids. Chains attached to a surface can instead give steric stabilization. Which effect occurs depends on surface affinity, chain size and concentration.

A cross-link connects different segments of a polymer network and restricts their independent motion. Permanent chemical cross-links commonly use covalent bonds; physical associations can instead have finite lifetimes. A connected permanent network can sustain long-time shear stress, whereas an uncrosslinked melt eventually flows. Cross-link density and network structure influence elastomer stiffness.

An elastomer is a polymeric material capable of large substantially recoverable deformation. Flexible chain segments supply configurational entropy, while a network of permanent or sufficiently long-lived cross-links prevents unrestricted macroscopic flow on the observation time scale. Its dynamic modulus depends on whether segmental relaxation can follow the imposed deformation. The rubbery plateau and high-frequency glassy response refer to different accessible relaxation regimes.

A biopolymer is a polymer produced by a living system, including proteins, nucleic acids and polysaccharides. Local chemical structure, sequence and interactions can give it stiffness or preferred conformations beyond those of an ideal chain. Biopolymer mechanics uses models such as the worm-like chain and the helix-coil transition model to represent those features.

A polymer with repeat-unit composition ${\mathrm{C}}_5{\mathrm{H}}_8$. Its cis-rich form is the main polymer component of natural rubber.