Practice question

Thickness hydrocarbon core typically three to four nanometers varies with chemical features not cellular energy currency. Acyl chain length linearly increases thickness about one point five angstrom per CH2; cis double bond shortens effective length kink reducing thickness. Cholesterol ordering straightens chains increasing thickness about four angstroms in fluid membranes by extending acyl conformations and reducing gauche defects. Integral proteins impose hydrophobic mismatch leading local thickening thinning compensated tilting clustering recruitment matching lipids as shown for SERCA rhodopsin potassium channels. Experiments X ray scattering small angle neutron scattering AFM confirm adjustments. ATP concentrations regulate activity P type ATPases ABC transporters flippases actin polymerization remodeling domains but do not change hydrocarbon chain length chemically. Depleting ATP halts active asymmetry yet freeze fracture electron microscopy shows lamellar thickness preserved. Therefore ATP availability uncoupled from bilayer dimensions unlike compositional factors distinguishing metabolic state structural parameter relevant membrane protein reconstitution crystallization and understanding mismatch sensing by Mga2 and Ire1 stress sensors in ER quality control pathways and unfolded protein response signaling.