A key characteristic of life is the ability to separate the external environment from the internal space. To do this, cells have evolved…

Cell membranes are composed of phospholipids, proteins, and carbohydrates loosely attached to one another through chemical interactions. Molecules…

The fluid mosaic model was first proposed as a visual representation of research observations. The model comprises the composition and dynamics of…

Adenosine triphosphate, or ATP, is considered the primary energy source in cells. However, energy can also be stored in the electrochemical gradient…

Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances,…

Approximately 60% to 95% of the weight of living organisms is attributed to water. Therefore, maintaining appropriate water balance within cells is…

The tonicity of a solution determines if a cell gains or loses water in that solution. The tonicity depends on the permeability of the cell membrane…

Tonicity describes the capacity of a cell to lose or gain water. It depends on the quantity of solute that does not penetrate the membrane. Tonicity…

The cell membrane—or plasma membrane—is an ever-changing landscape. It is described as a fluid mosaic as various macromolecules are embedded in…

The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and…

In contrast to passive transport, active transport involves a substance being moved through membranes in a direction against its concentration or…

One example of how cells use the energy contained in electrochemical gradients is demonstrated by glucose transport into cells. The ion vital to this…

Receptor-mediated endocytosis is a process through which bulk amounts of specific molecules can be imported into a cell after binding to cell…

Cells use energy-requiring bulk transport mechanisms to transfer large particles, or large amounts of small particles, into or out of the cell. The…

Cells pull particles inward and engulf them in spherical vesicles in an energy-requiring process called endocytosis. Phagocytosis (“cellular…

Exocytosis is used to release material from cells. Like other bulk transport mechanisms, exocytosis requires energy. While endocytosis takes…

Fluorescence correlation spectroscopy (FCS) is a powerful technique for studying the diffusion of molecules within biological membranes with high…

Membrane trafficking involves transport of proteins from the plasma membrane to the cell interior (i.e. endocytosis) followed by trafficking to…

Synaptic vesicles in functional nerve terminals undergo exocytosis and endocytosis. This synaptic vesicle recycling can be effectively analyzed using…