Chapter 5

Membranes and Cellular Transport

The Fluid Mosaic Model
The fluid mosaic model was first proposed as a visual representation of research observations regarding the composition and dynamics of membranes…
What is an Electrochemical Gradient?
5.2: What is an Electrochemical Gradient?
Adenosine triphosphate, or ATP, is generally considered the primary energy source in cells. However, energy can also be stored in the electrochemical…
Diffusion
5.3: Diffusion
Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances tend…
Osmosis
5.4: Osmosis
Approximately 60 to 95% of the weight of living things is composed of water. Therefore, maintaining appropriate water balance within cells is of…
Tonicity in Animals
5.5: Tonicity in Animals
Osmolarity is the total concentration of solutes in solution. If solutions with differing osmolarity are separated by a semi-permanent membrane that…
Tonicity in Plants
5.6: Tonicity in Plants
Tonicity is the quantity of a membrane impermeant solute in extracellular fluid that determines the magnitude and direction of osmosis and results in…
Facilitated Transport
5.7: Facilitated Transport
The chemical and physical properties of plasma membranes cause them to be selectively permeable. Since plasma membranes have both hydrophobic and…
Primary Active Transport
5.8: Primary Active Transport
In contrast to passive transport, active transport involves a substance being moved through membranes in a direction against its concentration and/or…
Secondary Active Transport
5.9: Secondary Active Transport
One example of how cells use energy contained in electrochemical gradients is demonstrated by glucose transport into cells, and the ion vital this…
Receptor-mediated Endocytosis
5.10: Receptor-mediated Endocytosis
Receptor-mediated endocytosis is a specialized form of pinocytosis, where molecules are actively taken into the cell. During the process, adaptor…
Pinocytosis
5.11: Pinocytosis
Pinocytosis is a type of endocytosis in which a cell engulfs any extracellular fluid that is present—including water and dissolved…
Phagocytosis
5.12: Phagocytosis
Another form of endocytosis is called phagocytosis or “cell eating” and occurs when receptors on the cell’s surface encounter a…
Exocytosis
5.13: Exocytosis
Exocytosis is the process in which substances produced inside a eukaryotic cell are secreted out through the fusion of membrane-bound vesicles to the…
Cell-surface Biotinylation Assay
5.14: Cell-surface Biotinylation Assay
A cell can regulate the amount of particular proteins on its cell membrane through endocytosis, following which cell surface proteins are effectively…
Immunology and Infection: Molecular Diffusion in Plasma Membranes
5.15: Immunology and Infection: Molecular Diffusion in Plasma Membranes
Biological membranes are complex and many factors influence functions such as protein diffusion. In this article, biologists use fluorescence…
Biology: Endocytosis and Recycling of Plasma Membrane Proteins
5.16: Biology: Endocytosis and Recycling of Plasma Membrane Proteins
Endocytic and recycling pathways are dynamic and involve the transport of molecules from the cell surface to its interior. In this article, an…
Neuroscience: Examination of Synaptic Vesicle Recycling
5.17: Neuroscience: Examination of Synaptic Vesicle Recycling
Synaptic vesicle recycling in stimulated cells can be analyzed using fluorescence. In this protocol, researchers use hippocampal neurons and FM dyes…