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Membrane Structure and Function, plasma membrane surrounds ALL cells
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- plasma membrane surrounds ALL cells
- membranes are composed mainly of phospholipids, lipids and proteins are the main components of membranes but carbohydrates are also important
- current model for animal plasma membrane
- held together by weak phobic interactions that make membrane fluid
- components can move laterally
- phospholipids are amphipathic molecules
- forms a bilayer with hydrophobic tails inside the membrane, and hydrophilic heads exposed to water on either side
- has both hydrophilic and hydrophobic parts
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a membrane is a collage of different proteins, often clustered in different groups embedded in the fluid matrix of the lipid bilayer
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- transport
- enzymatic activity
- signal transduction
- cell-cell recognition
- intercellular joining
- attachment to the cytoskeleton and extracellular matrix (EMC)
cell recognize each other by binding to molecules and many of these surface molecules are bonded to short, branched chains of carbohydrates.
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membrane exhibits selective permeability; some substances across more easily than others, the fluid mosaic model explains how membranes regulate molecular traffic across the membrane
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- it is the movement of particles of any substances so that they spread out evenly into the available spaces
- requires no energy
- substances diffuse down their concentration gradient, the region along which the density of a chemical substances increases or decreases
- high to low until it reaches equilibrium
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is the diffusion of free water (water molecules not clustered around another substance) across a selectively permeable membrane
the ability of a surrounding solution to cause a cell to gain or lose water, tonicity depends on the concentration of solutes in the solution that cannot cross the membrane, relative to that inside the cell
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transport proteins speed the passive movement of molecules across the plasma membrane, transport proteins include the carrier proteins and channel proteins
control the entry and exit of substances to and from the cell by means of a selectively permeable membrane
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- Active transport requires energy, usually in the form of ATP hydrolysis, to move substances against their concentration gradients
- all proteins involved in active transport are carrier proteins
- Bulk transport is moving a large amount of material across the cell membrane
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is a transport protein that generates voltage across a membrane, storing energy that can be used for cellular work
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moves 3 Na+ ions and 2 K+ ions out, main electro-genic mump in animals
macromolecules that are taken into the cell in vesicles, the membrane forms a pocket that deepens and pinches off forming a vesicle around the material for transport
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transport vesicles migrate to the membrane, fuse with it, and release their content outside the cell, many secretory cells use exocytosis to export their products
