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| A trait of plasma membranes that allows some substances to enter, but not others |
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| States that a membrane is a fluid structure with a "mosaic" of various proteins embedded in it |
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| A molecule containig both hydrophobic and hydrophilic regions. Phospholipids are aphipathic |
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| Proteins that are bound to the surface of a protein |
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Proteins that penetrate the hydrophobic core
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| Integral proteins that span the membrane |
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Membrane Protein Functions
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Transport
Enzymatic activity
Cell-cell recognition
Intercellular Trading
Attachment ro the cytoskeleton and extracellular matrix (ECM) |
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| Membrane carbohydrates covalently bonded to lipids |
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| Allow passage of hydrophillic substances across the membrane |
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| Channel proteins that facilitate the passage of water |
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| Transport proteins that bind to molecules and change shape to shuttle them across the membrane |
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The tendency for molecules to spread out evenly into available space
Although each molecule moves randomly, diffusion of a population of molecules may exhibit a net movemont in one direction |
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The difference of concentration of a substance from one area to another
Substances tend to diffuse down their concentration gradient |
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| Requires no energy from the cell to make it happen |
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The diffusion of water across a selectively permeable membrane
Water diffuses from the region of lower solute concentration to the region of higher solute concentration |
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| The ability of a solution to cause a cell to lose or gain water |
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| SOlute conentration is the same as that inside the cell, no net water movement across the plasma membrane |
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| Solute concentration is greater than that inside the cell; cell loses water |
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| Solute concntration is less than that inside the cell; cell gains water |
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| The control of water balance. It is a necessary adaptation for life in many environments |
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| When a plant cell in a hypotonic solution swells until the wall opposes uptake |
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| If a plant cell and it's surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp) and the plant may wilt |
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| In a hyperonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis |
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Transport proteins speed the passive movement of molecules across the plasma membrane
Channel proteins provide corridors that allow the specific molecule or ion to cross the membrane |
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| Channel proteins that open or close in response to a stimulus |
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Proteins that move substances across the concentration gradient
Requires energy, ususally in the form of ATP |
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The voltage difference across a membrane
Voltage is created by the differences in the distribution of positive and negative ions |
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Two combined forces that drive the diffusion of ions across a membrane:
A chemical force (the ion's concentration gradient)
An electrical force (the effect of the membrane potential on the ion's movement) |
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A transport protein that generates voltage across a membrane
Ex: The sodium potassium pump is the major electrogenic pump of animal cells |
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The main electrogenic pump of plants, fungi, and bacteria
[image] |
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When active transport of a solute indirectly drives transport of another solute
Ex: Plants commonly use the gradient of hydrogen ions generated by proton pumpts to drive active transport of nutrients into the cell [image] |
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| Transport vesicle migrate to the membrane, fuse with it, and release their contents |
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The cell takes in macromolecules by forming vesicles from the plasma membrane
Three Types:
Phagocytosis ("cellular eating")
Pinocytosis ("Cellular Drinking")
Receptor-mediated endocytosis
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Definition
A cell engulfs a particle in a vacuole
The vacuole fuses with a lysosome to digest a particle
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Molecules are taken up when extracellular fluid is "gulped" into tiny vesicles
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Receptor-Mediated Endocytosis
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Vesicle formation triggered by the binding of ligands to receptors
Ligands - Any molecule that binds specifically to a receptor site of another molecule |
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