| Criteria | Plasma Membrane | Nuclear Membrane | Remarks |
| Definition | The outermost boundary of the cell that encloses the cytoplasm | A double-membrane structure enclosing the nucleus | Both membranes serve as selective barriers but differ in structure, location, and function. |
| Structure | Single lipid bilayer composed of phospholipids, cholesterol, and proteins | Double lipid bilayer: inner and outer membranes separated by the perinuclear space | The nuclear envelope is more complex due to its double-membrane organization. |
| Composition | Lipid bilayer with embedded proteins (integral, peripheral), glycoproteins | Inner and outer membranes with nuclear pore complexes and associated proteins | Nuclear membrane is continuous with the rough ER and has specialized pore complexes. |
| Primary Function | Controls movement of substances in and out of the cell; communication and signaling | Protects genetic material; regulates transport between nucleoplasm and cytoplasm | Plasma membrane focuses on environmental interaction; nuclear membrane focuses on genome protection and regulation. |
| Selectivity | Selectively permeable: uses transport proteins, channels, and endocytosis mechanisms | Selectively permeable via nuclear pore complexes (NPCs) | Nuclear transport is tightly regulated by NPCs and nuclear localization/export signals. |
| Presence of Pores | No fixed pores; uses channels and transporters dynamically | Contains large proteinaceous nuclear pores (30–50 nm in diameter) | Only nuclear membrane has permanent, structured pores. |
| Connection to Organelles | Continuous with extracellular space and connected to some organelles via vesicles | Outer membrane is continuous with rough endoplasmic reticulum | Nuclear envelope is a specialized extension of the ER system. |
| Associated Processes | Cell signaling, transport, cell adhesion, ion exchange, receptor-mediated responses | DNA replication, transcriptional regulation, nuclear import/export of macromolecules | Plasma membrane supports extracellular interaction; nuclear membrane governs nuclear-cytoplasmic exchange. |
| Dynamics | Highly fluid and dynamic; undergoes remodeling during endocytosis, exocytosis | Disassembles and reassembles during mitosis (in eukaryotic cells) | Plasma membrane maintains cell boundary; nuclear membrane disassembles during cell division and reforms afterward. |
| Enzymatic Activity | Contains enzymes for signal transduction (e.g., kinases, phosphatases) | Contains fewer enzymes; associated with chromatin anchoring and RNA processing factors | Enzymatic role of nuclear membrane is minimal and structural. |
| Proteins Associated | Receptors, transporters, glycoproteins, structural proteins (e.g., spectrin, actin) | Nuclear pore complex proteins (nucleoporins), lamins (on inner membrane) | Specialized protein complexes define the functions of each membrane. |
| Role in Cell Division | Remains intact in many eukaryotes during interphase and reorganizes at cytokinesis | Disassembles during prophase and reassembles in telophase | Nuclear envelope breakdown is critical for chromosome segregation in mitosis. |
| Presence in Cell Types | Present in all cell types: prokaryotic and eukaryotic | Present only in eukaryotic cells | Prokaryotes lack a nuclear membrane; DNA is in nucleoid region. |
| Lipid Composition | Rich in cholesterol and sphingolipids | Similar lipid composition to ER; outer membrane resembles ER membrane | Cholesterol helps maintain fluidity in plasma membrane; nuclear membrane is more rigid and specialized. |
| Structural Support | Supported by cytoskeleton (actin filaments, microtubules) | Inner membrane is supported by the nuclear lamina (intermediate filament network) | Nuclear lamina maintains nuclear shape and anchors chromatin. |
| Repair and Remodeling | Actively repaired and remodeled during membrane damage or signaling | Reassembled from ER vesicles and nuclear components post-mitosis | Plasma membrane repairs locally; nuclear membrane disassembles and reforms as a unit. |
