Protein Folding, Oxygen Binding and Allostery: every key term you need (+ practice quiz)
25 flashcard terms for Biochemistry Topic 3, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
The observation that a denatured protein can refold spontaneously to its active form, showing that the folding information is contained in the sequence itself.
Folding funnel
A model in which many high-energy conformations flow down parallel routes toward one low-energy native state, explaining why folding is fast despite an astronomical number of possible shapes.
Molten globule
A partly folded intermediate with native-like compactness and secondary structure but no fixed side-chain packing.
Chaperone
A protein that binds exposed hydrophobic patches on unfolded chains to prevent aggregation. It raises the yield of correct folding without dictating the final structure.
Chaperonin
A barrel-shaped chaperone complex that encloses a single substrate chain in an isolated chamber and uses cycles of nucleotide hydrolysis to give it repeated folding attempts.
Amyloid fibril
An ordered aggregate in which misfolded chains stack into extended beta sheets. Its extreme stability is why amyloid deposits accumulate rather than clear.
Prosthetic group
A non-protein component permanently attached to a protein and required for its function, such as the heme of a globin.
Heme
A porphyrin ring holding a central iron ion. It binds oxygen reversibly only when the iron stays in the ferrous state and is shielded from oxidation by the surrounding protein.
Proximal histidine
The residue that coordinates heme iron from the protein side. Its movement on oxygen binding is the mechanical signal that propagates the conformational change.
Distal histidine
The residue on the binding face of heme that hydrogen bonds bound oxygen and sterically discourages carbon monoxide, sharply reducing an otherwise lethal affinity.
Myoglobin
A single-chain oxygen storage protein of muscle. It has no subunit interfaces, so its binding curve is hyperbolic and it releases oxygen only at very low partial pressure.
Hemoglobin
A tetramer of two alpha and two beta chains that transports oxygen in blood. Its subunit interfaces convert simple binding into cooperative, regulated delivery.
Cooperativity
Binding at one site changes the affinity of the remaining sites. It produces a sigmoidal curve and makes the fraction bound highly sensitive to small concentration changes.
Hill coefficient
A number summarizing cooperativity. Above one indicates positive cooperativity, one indicates independent sites, and below one indicates negative cooperativity.
T state
The low-affinity quaternary conformation, stabilized by ion pairs across subunit interfaces and favoured in actively respiring tissue.
R state
The high-affinity quaternary conformation reached after those interface ion pairs break, favoured in the lungs where oxygen is plentiful.
Concerted model
Treats all subunits as switching between two states together, so the whole molecule is either low affinity or high affinity and no mixed forms exist.
Sequential model
Allows subunits to change one at a time, so ligand binding induces a local change that alters neighbouring subunits and mixed states are permitted.
Bisphosphoglycerate effect
A small phosphorylated metabolite binds in the central cavity of the low-affinity state, stabilizing it and forcing more oxygen release in the tissues.
Bohr effect
Falling pH and rising carbon dioxide lower oxygen affinity, so metabolically active tissue automatically triggers greater unloading.
Carbamate formation
Carbon dioxide reacts with amino-terminal groups of hemoglobin, adding negative charge that stabilizes the low-affinity state and helps carry carbon dioxide back to the lungs.
Fetal hemoglobin
A variant whose gamma chains bind the regulatory bisphosphoglycerate weakly, raising oxygen affinity so that oxygen transfers from maternal to fetal blood.
Sickle cell substitution
A single glutamate to valine change on the beta chain surface creates a hydrophobic patch that lets deoxygenated molecules polymerize into fibres, deforming the cell.
Allosteric effector
A ligand that binds away from the active site and shifts the equilibrium between conformational states, changing activity without competing with substrate.
Homotropic effect
Regulation in which the substrate itself acts as the allosteric signal, as oxygen does for hemoglobin, in contrast to a separate heterotropic regulator.