Which of the following is not a function of the plasma membrane?
Plasma membrane confers cell individuality by separating intracellular milieu from external environment and actively regulating exchange to maintain homeostasis. Its phospholipid bilayer plus embedded transport machinery including Na+/K+ ATPase establishing 140 mM potassium inside and 145 mM sodium outside, glucose carriers GLUT family facilitating uptake, amino acid exchangers, and aquaporins ensuring selective permeability and volume control, together with tight junctions restricting paracellular diffusion. Signaling platforms include receptor tyrosine kinases like EGFR that dimerize upon EGF binding activating Ras-MAPK and PI3K-Akt cascades, heterotrimeric GPCRs coupling to adenylyl cyclase producing cAMP activating PKA, and integrins linking extracellular matrix fibronectin and laminin to actin cytoskeleton for mechanotransduction via focal adhesion kinase. Glycoproteins and glycolipids presenting sialylated and fucosylated epitopes mediate cell-cell recognition essential for immune surveillance, tissue patterning, and blood grouping. Protein synthesis occurs elsewhere: cytosolic free 80S ribosomes translate cytosolic proteins, ER-bound ribosomes synthesize secretory proteins translocated via Sec61 channel, with mRNA processing in nucleus. Therefore synthesis of proteins is not intrinsic plasma membrane function.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Plasma Membrane Functions Overview.