Chapter 5
Membranes and Cellular Transport

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

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

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

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

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

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

Tonicity in Animals
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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 in Plants
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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…

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

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

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

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

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

Exocytosis
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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…

The Cell-based L-Glutathione Protection Assays to Study Endocytosis and Recycling of Plasma Membrane Proteins
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Membrane trafficking involves transport of proteins from the plasma membrane to the cell interior (i.e. endocytosis) followed by trafficking to…