What are cell membranes? What are the physiological functions of biological membranes? Eukaryotic cells and their organelles are enveloped by viscoelastic layers made of lipids and proteins. These layers are generally referred to as cell membranes and when they surround the entire cell, they [...]

What is the plasma membrane? Plasma membranes are subcellular structures, approximately 10nm thick, that form a protective boundary around the cell as well as the cell’s organelles. They serve to both impede foreign material from entering the cell, and prevent the cellular contents from [...]

How do mechanically-gated ion channels facilitate mechanotransduction? Mechanotransduction relies on the ability of cells to convert mechanical cues, such as stretch or compression, to biochemical signals. One way this occurs is through the activity of mechanically-gated ion channels. Calcium ions channels: Physiologically, calcium ions [...]

How do lipid bilayer components move? One of the tenets of the Fluid-Mosaic membrane model is that the components of the bilayers are free to move. Before describing the differences between lipid and protein movement in the bilayer, it is important to consider the [...]

Why are membrane lipids asymmetrical? The human red blood cell is functionally specialized for transporting oxygen. In order to maximize oxygen capacity, it has no nucleus or organelles, consisting primarily of plasma membrane and hemoglobin. This made it an ideal candidate for membrane studies. [...]

What is membrane curvature? Membrane curvature refers to the physical bending of membranes to accommodate various cell morphology changes as well as the formation of membrane-bound transport intermediates like spherical vesicles or tubules. As membranes are inelastic and resistant to spontaneous bending, membrane curvature [...]

What is Membrane Trafficking? Membrane trafficking encompasses the wide variety of processes that go into the movement of cargo (typically proteins, pathogens and other macromolecules) using membrane bound transport vesicles. This transport can take place within different organelles in the same cell, or across [...]

What is caveolar endocytosis? Caveolar endocytosis is a clathrin-independent endocytic process which involves bulb-shaped, 50-60nm plasma membrane invaginations called caveolae (or ‘little caves’). Caveolae formation is driven by integral membrane proteins called caveolins as well as peripheral membrane proteins called cavins (reviewed in [1]). [...]

What is clathrin-mediated endocytosis? Clathrin-mediated endocytosis (CME) is a vesicular transport event that facilitates the internalization and recycling of receptors engaged in a variety of processes, including signal transduction (G-protein and tyrosine kinase receptors), nutrient uptake and synaptic vesicle reformation [1]. Two classical examples [...]

How is clathrin recruited to the plasma membrane? Clathrin-mediated endocytosis is triggered by phosphatidylinositol-4,5-bisphosphate (PIP2) accumulation within the plasma membrane. PIP2 accumulates as a result of phosphoinositide catalysis by the lipid kinases, phosphatidylinositol-4-kinase (PI4K) and phosphatidylinositol-4-phosphate-5-kinase (PI4P5K) [1], [2] and hydrolysis by phosphatases. The [...]

How does the clathrin coated pit form? Adaptor proteins such as AP-2, AP180 and CALM (Clathrin-assembly lymphoid myeloid leukaemia protein), which accumulate within the lipid bilayer, are responsible for the recruitment of the triskelion shaped Clathrin trimer. This trimer does not interact with the [...]

How does invagination and maturation of the clathrin-coated vesicle occur? Clathrin-coated vesicle maturation incorporates the activities of a range of proteins. Actin, myosin and WASP all have important roles in the formation and stabilization of clathrin-coated pits (CCPs) [1][2][3]. Evidence also suggests that F-actin [...]