Practice question

Electric field across membrane influenced anionic phospholipids clustered inner leaflet physiological pH seven point four generating negative surface potential crucial signaling recruitment. Phosphatidylserine headgroup contains phosphate pKa less two carboxyl pKa three amine pKa nine net charge minus one neutral pH despite zwitterionic potential measured zeta minus fifteen millivolts inner leaflet ten to fifteen percent total phospholipid outer almost zero. Approximately PS binds Annexin V calcium dependent detection apoptosis C2 domains PKC synaptotagmin polybasic KRas via electrostatic attraction enriching signaling inner surface recruitment MARCKS Effector Domain. Phosphatidylcholine quaternary ammonium constitutive positive balancing phosphate net neutral zero, sphingomyelin similarly neutral zwitterion with phosphocholine head balanced, cholesterol neutral small hydroxyl uncharged only. Maintaining PS inside requires ATP11C flippase CDC50A complex ATP dependent; externalization during apoptosis creates electronegative patch recognized phagocyte TIM receptors stabilin-2 BAI1 initiating clearance. Understanding negative charge carrier explains why inner leaflet more negative recruiting polybasic proteins why calcium influx upon activation neutralizes PS facilitating membrane fusion and blood coagulation tenase prothrombinase complexes assembly PS rich platelet surface supporting clotting amplification mechanisms thoroughly examined physiology and cell biology and immunology.